Acids, Bases and Salts : Complete Set of Questions



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This set of questions contains all the possible concepts
which could be asked in the examination

Acids and Bases

Q.1 Define acid and list  its  two chemical properties?

Acids - Acids are compounds which give hydrogen ion in water solution. For example, Hydrochloric acid (HCl), Sulphuric acid(H2SO4), Nitric acid(HNO3).

Two properties of acids :

(i) Acids reacts with metal to form salt and hydrogen gas.

(ii) Acids react with metal carbonate or metal hydrogen carbonate to produce salt, carbon dioxide and water.


Q.2 What  is neutralization reaction? Give two examples?   

Neutralization Reaction 

An acid neutralizes a base when they react with each other and respective salt and water are formed.

Acid + Base → Salt + Water

Since in the reaction between acid and base both neutralize each other, hence it is also known as neutralization reaction.

Example

• Sodium chloride and water are formed when hydrochloric acid reacts with sodium hydroxide (a strong base).


• In similar way, calcium chloride is formed along with water when hydrochloric acid reacts with calcium hydroxide (a base).


Q.3 Complete the following reactions and write the name of the metallic compounds obtained :
(a) MgO + H2SO4 →

(b) Al2O3 +HCl →

(a) MgO  + H2SO4 →  MgSO4 + H2O

(b) Al2O3 + 6HCl → 2AlCl3 + 3H2O                                     


Q.4 List in tabular form two differences between an acid and a base based on their chemical properties?   


Q.5 Give reason, why aqueous-solution of an acid conducts electricity?

When acids dissolved in water they produce H+ ions and due to formation of these mobile ions in aqueous solution of acids, it conducts electricity.


Q.6 A solution reacts with crushed egg shells to give a gas that turns lime water milky, name the gas evolved?

The egg shells are made up of CaCOand the gas which turns lime water milky is carbon dioxide.


Q.7 How will you test for the gas which is liberated when hydrochloric acid reacts with an active metal?

When an active metal reacts with hydrochloric acid, Hydrogen gas is liberated. We will test the presence of hydrogen gas by bringing a burning candle near the mouth of the test tube in which the reaction is taking place if the gas burns with a popping sound, then it can be concluded that it is a Hydrogen gas.


Q.8 Name the gas evolved when dilute hydrochloric acid reacts with sodium hydrogen carbonate. How is it recognized ?

When dilute hydrochloric acid reacts with sodium hydrogen carbonate, Carbon dioxide gas is liberated .We recognize the presence of carbon dioxide by passing it through lime water which turns milky or a white precipitate of calcium carbonate is formed. This confirms that the gas is carbon dioxide.


Q.9  Explain strong acids and weak acids with examples?

Strong acids ionize fully in water to produce large number of H+ ions. For example, Hydrochloric acid (HCl), Sulphuric acid(H2SO4), Nitric acid(HNO3), Hydrobromic acid(HBr).

Weak acids ionize partially in water to produce small number of H+ ions. For example, carbonic acid(H2CO3), phosphoric acid(H3PO4), sulphurous acid(H2SO3), acetic acid(CH3COOH).


Q.10 How is the concentration of hydronium ions (H3O+) affected when the solution of an acid is diluted ?

• If concentrated acid (or base) is mixed with water, concentration of hydronium ions H_3^ + O decreases. So the acid or base becomes dilute.

• The phenomena of changing concentrated acid / base into dilute acid / base (respectively) is an exothermic reaction.


Q.11 Write word equation and then balanced equations for the reactions taking place when :

(a) dilute sulphuric acid reacts with zinc granules.

(b) dilute hydrochloric acid reacts with magnesium ribbon.

(c) dilute sulphuric acid reacts with aluminum  powder.

(d) dilute hydrochloric acid reacts with iron filings.

(a) {H_2}S{O_4}\left( {aq} \right) + Zn\left( s \right) \to ZnS{O_4}\left( {aq} \right) + {H_2}\left( g \right)

(b) 2HCl\left( {aq} \right) + Mg\left( s \right) \to MgC{l_2}\left( {aq} \right) + {H_2}\left( g \right)

(c) 2{H_2}S{O_4}\left( {aq} \right) + 2Al\left( s \right) \to A{l_2}{\left( {S{O_4}} \right)_3}\left( {aq} \right) + 3{H_2}\left( g \right)

(d) 6HCl\left( {aq} \right) + 2Fe\left( s \right) \to 2FeC{l_3}\left( {aq} \right) + 3{H_2}\left( g \right) 


Q.12 Complete and balance the following chemical equations

(a) Zn (s) + HCl (aq)

(b) Na2CO3 (s) + HCl (aq)

(c) NaHCO3 (s) + HCl (aq)

(d) NaOH (aq) + HCl (aq)

(e) CuO(s)  + HCl (aq)→

(a) Zn(s) + 2HCl (aq) → ZnCl2(aq) + H2(g)

(b) Na2CO3(s) + 2HCl (aq) → 2NaCl (aq) + CO2 (g) + H2O (l)

(c) NaHCO3 (s) + HCl(aq) → NaCl(aq) + H2O (l) + CO2 (g)

(d) NaOH(aq) + HCl(aq) → NaCl(aq) + H2O (l)

(e) CuO (s) + 2HCl (aq)  → CuCl2 (aq) + H2O (l)


Q.13  What happens when an acid reacts with metal ? Give chemical equation of the reaction involved?

Reaction of acids with metal -

Acids give hydrogen gas along with respective salt when they react with a metal. 

Example :

• Hydrogen gas and zinc chloride are formed when hydrochloric acid reacts with zinc metal.

Zn + 2HCl\left( I \right) \to ZnC{l_2}\left( s \right) + {H_2}


Q.14 While diluting an acid/base , why is it recommended that the acid should be added to water and not water to the acid/base ?

• Always add concentrated acid/base to water; not water to concentrated acid/base.

• When concentrated acid is added to water, heat is released gradually. This heat is absorbed by large amount of water to increase its temperature.

• When water is added to concentrated acid, heat is released suddenly. This heat vaporizes small amount of water to steam. This steam is splits out with drops of concentrated acid which can damage our body. So always add concentrated acid to water, not water to concentrated acid. Same is true with base also.


Q.15 What happens when an acid reacts with a base ? Explain by taking the example of hydrochloric acid and sodium hydroxide. Give equation of the chemical reaction which takes place. What is the special name of such a reaction ?

An acid neutralizes a base when they react with each other and respective salt and water are formed.

Acid + Base → Salt + Water

Since in the reaction between acid and base both neutralize each other, hence it is also known as neutralization reaction.

Example:

• Sodium chloride and water are formed when hydrochloric acid reacts with sodium hydroxide (a strong base).


 Q.16 What happens when an acid reacts with a metal oxide ? Explain with the help of an example. Write a balanced equation for the reaction involved.

Acids give water along with respective salt when they react with a metal oxide.

Metal + acid → Respective salt + Water

Example :

• Water and sodium chloride are formed when hydrochloric acid reacts with sodium oxide.

Na2O + 2HCl (aq)→ 2NaCl + H2O


Q.17 Name one natural source of each of the following acids :

(a) Citric acid

(b) Oxalic acid

(c) Lactic acid

(d) Tartaric acid



Q.18 Name one animal and one plant whose stings contain formic acid (or methanoic acid ).     

Animal sting containing formic acid: Ant sting
Plant sting containing formic acid: Nettle leaf sting


Q.19 (a) What are organic acids and mineral acids ?

(b) Give two examples each of organic acids and mineral acids.

(c) State some of the uses of mineral acids in industry.

(a) Organic acids: An organic acid is an acid that is found naturally in plants and animals. Generally organic acids are weak acids and do not dissociate completely in water.

Mineral acids : Mineral acids are man-made and are derived from one or more inorganic compounds. They are also known as inorganic acids. They range from acids of great strength to those that are very weak.

(b) Here are a few common examples:

Organic acids:

Lactic acid

Citric acid

Mineral acids:

Hydrochloric acid (HCl)

Nitric acid (HNO3)

(c)Uses of mineral acids in industry :

Mineral acids are used in many sectors of the chemical industry for the synthesis of various chemicals.

Dilute  solutions of hydrochloric acid are used for removing the deposits form inside boilers, with precautions to prevent the corrosion of the boilers by the acid.

They are also used in the processing of leather, purification of common salt, construction of buildings, etc.


Q.20 Classify the following into strong acids and weak acids :

HCl, CH3COOH, H2SO4, HNO3, H2CO3, H2SO3

Strong acid – HCl, H2SO4, HNO3

Weak acid – CH3COOH, H2CO3, H2SO3   


Q.21 Why do HCl, H2SO4, HNO3, etc, show acidic character in aqueous solutions while solutions of compounds like C6H12O6 (glucose) and C2H5OH (alcohol) do not show acidic character ?

HCl, H2SO4 , HNO3 etc. show acidic character in aqueous solutions, whereas solutions of compounds such as C6H12O6 (glucose) and C2H5OH (alcohol) do not show acidic character because HCl, H2SO4, HNO3, etc. dissociate in aqueous solutions to give H+ (aq) ions, which are a vital part of an acid and determine the acidic property of acids.
C6H12O6 (glucose) and C2H5OH (alcohol) do not dissociate in aqueous solution even though they contain hydrogen atoms.


Q.22 Why acid is not stored in metallic containers. Give reason?

Acid is not stored in metallic containers because acids and metals can easily react. Acids react with metals to give hydrogen gas.Curd and other foodstuffs (such as lemon juice) are acidic in nature. Hence, when these acidic foodstuffs are  kept in metal containers, hydrogen gas is liberated , and it spoils food.


Q.23 Name the gas evolved when zinc granules are treated / heated with:

(a) hydrochloric acid solution

(b) sodium hydroxide solution

(a) When zinc granules are treated with hydrochloric acid, zinc chloride is formed and hydrogen gas is liberated

Zn (s) + 2HCl(aq) → ZnCl2(aq) + H2(g)

(b) Zinc reacts with sodium hydroxide giving sodium zincate and hydrogen gas

Zn (s) + 2NaOH(aq) → Na2ZnO2(aq) + H2(g)   


Q.24 What is the common name of  water soluble bases ? 

Water soluble bases are commonly known as alkalies. An alkali is a unique base that dissolves in water without any chemical reaction. All alkalies are bases whereas only some bases are alkalies.


Q.25 Which chemical is injected into the skin of a person :

(a) during an bee sting ?

(b) during the wasp sting ?

How can the effect of these stings be neutralized?

(a) When a bee stings a person, it injects an acidic solution into the person’s skin. This causes severe pain and irritation. The remedy is to apply a baking soda solution which is a basic in nature. The solution relief's the pain by neutralizing the acid.

(b) When a wasp stings a person, it inserts an alkaline solution into the person’s skin. This causes severe pain  and irritation. The remedy is to apply a weak acid, such as vinegar, to the wound.. The acid neutralizes the alkaline solution and relief the pain.


Q.26 (a) Define an acid and a base. Give two examples of each.

(b) Give the names and formulas of two strong bases and two weak bases.

(c) What type of ions are formed :

(i) When an acid is dissolved in water ?

(ii) When a base  is dissolved in water ?

(d) Write the neutralization reaction between acids and bases in terms of the ions involved.

(e) Write any two important uses of bases. 

(a) Acids – Acids are compounds which give hydrogen ion in water solution. For example, Hydrochloric acid HCl), Sulphuric acid (H2SO4), Nitric acid (HNO3).

Bases – Bases are compounds which give hydroxide ion in water solution. For example, Sodium hydroxide (NaOH), Potassium hydroxide (KOH), Calcium hydroxide (Ca(OH)2)

(b) Strong bases ionize fully in water  to produce large number of OH– ions. For example, sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH) and Calcium hydroxide (Ca(OH)2).

NaOH(aq) → Na+ +OH–

Weak bases ionize partially in water to produce small number of OH– ions. For example magnesium hydroxide (Mg(OH)2), ammonium  hydroxide (NH4OH).

(c) The type of ions formed are explained below

(i) When an acid is dissolved in water, it ionises to produce hydronium ions (H3O+)

(ii) When a base is dissolved in water, it ionises to produce hydrogen ions (OH+ ions)

(d)   Neutralization Reaction –

An acid neutralizes a base when they react with each other and respective salt and water are formed

Acid + Base → Salt + Water

Since in the reaction between acid and base booth neutralize each other, hence it is also known as neutralization reaction.

Equations involving ions :

Hydrochloric acid ionises in water as follows

HCl (aq) → H+(aq) + Cl(aq)

Sodium hydorxide ionises in water as

NaOH(aq) → Na+(aq) + OH+(aq)

Let us now combine both the reactions above

Na+(aq)  + Cl(aq) + H+(aq) + OH(aq)  NaCl(aq) + H2O(l)

(e) Two important uses of base:

Sodium hydroxide (base) is used to form soap, paper and fibre.

Calcium hydroxide (base) is used in bleaching powder.


Q.27 What happens when bases react with non-metal oxides?  Explain with the help of an example. What does this reaction tell us about the nature of non-metal oxides?

Reaction of bases with non-metal Oxides :

Non-metal oxides is a chemical compound that contains oxygen and one non-metal in its chemical formula. For example, carbon dioxide (CO2), sulphuric dioxide (SO2).

Bases react with non-metal oxides to form a salt and water

Bases + Non-metal oxides  → Salt + Water

Example :

2NaOH(aq) + CO2(g) → Na2CO3(aq) + H2O(l)

Here, sodium hydroxide (base) reacts with carbon dioxide (non-metal oxide) to give sodium carbonate (salt) and water.

This reaction tell us that non-metal oxides are acidic in nature.


Q.28 Write down various uses of acids and bases?

Uses of Acids and Bases :

Sulphuric acid is used to make fertilizers, dyes, chemicals, plastics, fibres, detergent, explosives, car batteries.

Nitric acids is used to make fertilizers, explosives (TNT – Tri Nitro Toluene), dyes, plastics.

Hydrochloric acid is used to form dye, in textile industry, food and leather industry, removing metal oxide films from steel objects.

Sodium hydroxide (base) is used to form soap, paper, fibre.

Calcium hydroxide (base) is used in bleaching powder.


Q.29 Write down the types of acids on the basis of their occurrence with example?

Types of Acids :

Acids can be divided into two types on the basis of their occurrence –

(i) Natural acids

(ii) Mineral acids

Natural Acid : Acids which obtained from natural sources (plants and animals) are called natural acid or organic acid.

Mineral Acids : Acids that prepare from mineral are known as mineral acids/inorganic acids/man-made acids or synthetic acid, such as hydrochloric acid (HCl), sulphuric acid (H2SO4), nirtic acid (NHO3), etc. 


Q.30  What happen when base react with metal, explain it with example?

Reaction of Base with metal :

When base react with metal, it produces salt and hydrogen gas.

Alkali + metal → Respective salt + hydrogen gas

Example :

Sodium hydroxide gives hydrogen gas and sodium zincate when reacts with zinc metal.

2NaOH\left( {aq} \right) + Zn\left( s \right) \to N{a_2}Zn{O_2}\left( {aq} \right) + {H_2}


Q.31 Explain the reaction of carbonates and bicarbonates with acids?

Reaction of Carbonates with Acids:

Acids give carbon dioxides gas and respective salts along with water when they react with carbonates.

Carbonate + acid → Salt + carbon dioxide + water

Examples :

Hydrochloric acid gives carbon dioxide gas, sodium chloride along with water when reacts with sodium carbonate.

N{a_2}C{a_3} + 2HCl \to 2NaCl + C{O_2} + {H_2}O

Reaction of Acid with Bicarbonates –

Acids give carbon dioxide gas, respective salt and water when they react with bicarbonate.

Acid + bicarbonate →  Salt + carbon dioxide + water

Examples :

Hydrochloric acid gives carbon dioxide, sodium chloride and water when it reacts with sodium bicarbonate.

NaHC{O_3} + HCl \to NaCl + C{O_2} + {H_2}O

In general, if we use weak acids, reaction will be slow and if we use strong acids, reactions will be fast.


Q.32 Like acids, compounds such as alcohol and glucose also contain hydrogen but these compounds are not categorized as acids. Why?

Substances which contains hydrogen are considered to be acids. Acids when dissolved in water produce H+ ions. But glucose and alcohol do not produce H+   ions when dissolved in water. So, they are not categorized as acids.


Q.33 Describe an activity with labeled diagram to show how acid and base react with metal?

Experiment to Show how do Acid and Base react with Metal : 

• Set apparatus as above

• Take zinc granules in a test tube and put dilute suphuric acid in it

• You will see small bubbles of hydrogen gas in test tube

• Pass the gas through soap solution.

• Soap bubble will be formed with the gas inside.

• Take a burning candle near bubbles.

• If the candle burns with pop sound, then it confirms the evolution of hydrogen gas. Burning with pop sound is the characteristic test for hydrogen gas.


Q.34 Describe an activity how metal oxides react with acid?

• Take small amount of black copper oxide in a test tube.

• Pour some dilute HCl slowly in test tube.

• Keep stirring.

• We observe a bluish – green solution due to formation of copper chloride.


Q.35 What happens when carbon-dioxide gas is passed through lime water for a short time?Write equations of the reactions involved.

When carbon dioxide gas is passed through lime water, the lime water turns milky. This confirms that the gas liberated in the reaction is none other than carbon dioxide.

The reaction that occurs when carbon dioxide is passed through lime water for a short time can be represented as follows :

Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)


Q.36 Explain the corrosive nature of acids and bases?

Corrosive Nature of Acids and Bases –

Acids and bases are corrosive in nature. They damage / destroy the substances with which they come into contact.

Strong acids and bases are more corrosive while weak acids and bases are less corrosive.

Specially concentrated weak acids and bases are not corrosive.

Generally Dilute weak acids and bases are not corrosive. Dilute acids are found in fruits and vegetable and we eat them in our meal because they are not corrosive. But concentrated weak acids and bases are corrosive in nature.

This symbol is used to warn us for corrosive substances.


Q.37 Explain how, several monuments like Tajmahal become yellowish due to acid rain?

Acid rain causes damage to the historical monuments and other buildings. For example Tajmahal, which is made of marble, is getting damaged because of reaction with acid rain. Marble is calcium carbonate which reacts with the acid and thus gets corroded.


Q.38 Explain the behavior of acids and bases in the absence of water?

Acids and Bases in absence of Water:

A dry acid does not dissociate in hydrogen ions. When we dissolve it with water, then it shows the acidic behavior.

For example, dry hydrochloric acid (gas) does not change the colour of blue litmus paper to red because a dry acid does not dissociate hydrogen ion. This is the cause that a moist litmus paper is used to check the acidic or basic character of a gas.

Similarly at room temperature, sodium hydroxide is in the form of solid. So as a solid, NaOH does not dissociate into hydroxide ion. When we dissolve it with water, then it shows its basic behavior.


pH SCALE

Q.39 Define pH scale and its range?

pH is a scale which quantities the concentration of hydrogen ion in a solution. The range of pH scale is between 0 to 14. The pH value increases with decrease in hydrogen ion concentration.

If the value of pH is 0, this shows maximum hydrogen ion concentration.

pH value equal to 14 shows lowest hydrogen ion concentration.


Q.40 What is meant by p and H in pH?

p in pH stands for "potenz" in Germany and H for hydrogen.


Q.41 What are antacids? Explain their role in providing relief from stomach ache.

Antacids are mild bases. They neutralize the effect of extra acid produced in the stomach during indigestion and thus provide relief. 


Q.42 Three solutions A, B, C has pH as follows: 1, 5 and 8. Predict their nature and arrange in increasing order of their acidic strength?

The solutions A and B are acidic (<7) while C is slightly alkaline (>7). Increasing order of their strength = A > B > C.


Q.43 Two solutions A and B have pH values of 3.0 and 9.5 respectively. Which of these will turn blue litmus red and which will turn phenolphthalein from colourless to pink? Predict their nature also. Give reason for your answer.

The solution A will turn the blue litmus red because it is an acidic solution (pH is less than 7).

The solution B will turn phenolphthalein from colourless to pink because it is a basic solution (pH is more than 7).


Q.44 Give two practical applications of neutralization reaction?

1. Antacids have been developed on the basis of neutralization reaction.

2. Tooth pastes are basic in nature which neutralizes the excess of acid produced in our mouth.


Q.45 (a) What is an indicator? Name three common indicators.

(b) Name the acid-base indicator extracted from lichen.

(c) What colour does the turmeric paper turn when put in an alkaline solution?

(a) Indicators are substances that show a distinct change (colour or odour) simultaneous to a change in concentration of ions such as H+ and OH ions.

Three common indicators are  Methyl orange, phenolphthalein and litmus solution.

(b) A purple dye is extracted from a plant called lichen. This dye is called a litmus solution and is commonly used as acid-base indicator.

(c) When turmeric paper is put into an alkaline solution, it turns red.


Q.46 What is an olfactory indicator? Name two olfactory indicators. What is the effect of adding sodium hydroxide solution to these olfactory indicators?

Olfactory Indicators :

Substances which change their smell when mixed with acid or base are known as olfactory indicators.

Two olfactory indicators are onion and vanilla.

when sodium hydroxide solution is added to an olfactory indicator it loses its characteristic smell.


Q.47 Explain various types of acid-base indicators?

Substances which identify/show the acidic or basic behavior of other substance by change in colour are known as acid-base indicators.

Type of Indicator: There are many types of indicators. Some common types of indicators are

• Natural Indicator

• Synthetic Indicator

• Olfactory Indicator

• Universal Indicator

Natural Indicator: Indicators obtained from natural sources are called natural indicators. Litmus, turmeric etc. are some common natural indicators used widely to show the acidic or basic character of substances.

Synthetic Indicator: Indicators that are synthesized in laboratory are known as synthetic indicators. For example: phenolphthalein, methyl orange, etc.

Olfactory Indicators: Substances which change their smell when mixed with acid or based are known as olfactory indicators. For example onion, vanilla, clove, etc.

Universal Indicator: Using a litmus paper, phenolphthalein, methyl orange, etc. only the acidic or basic character of a solution can be determined, but use of these indicators does not give the idea about the strength (pH value) of acid or base. So, to get the strength as well as acidic and base nature of a given solution, universal indicator is used.


Q.48 What is the name of the indicator which can be used for testing the pH  of a solution?

A universal indicator shows different colours at different concentrations of hydrogen ions in a solution and can be used for testing the pH of a solution.


Q.49 What colour will universal indicator show if you add it to the following substances?

(a) Potassium hydroxide, pH = 12

(b) Soda water, pH = 5

(c) Sulphuric acid, pH = 2


Q.50 A beaker of concentrated hydrochloric acid has a pH of 1. What colour will full range universal indicator turn if it is added to this beaker? Is it a strong or a weak acid? 

When full range universal indicator is added to the beaker containing concentrated hydrochloric acid with a pH of 1 it will  impart a red colour to it.

As the pH value decreases from 7, the acidity increases, as there is an increase in the concentration of hydrogen ions (H+). So, the given acid is very strong.


Q.51 Two solutions X and Y are tested with universal indicator. Solution X turns orange whereas solution Y turns red. Which of the solutions is a stronger acid?

Solution Y is stronger because the red colour indicates a pH value of 1, whereas the orange colour indicates a pH value higher than 1.


Q.52 Two drinks P and Q gave acidic and alkaline reactions, respectively. One has a pH value of 9 and the other has a pH value of 3. Which drink has the pH value of 9?

Drink Q will have a pH value of 9, because basic solutions have a pH greater than 7 on a pH scale.


Q.53 Two solutions X and Y have pH=4 and pH=8, respectively. Which solution will give alkaline reaction and which one acidic?

As per the given data, solution X has a pH value of 4(<7) and will give an acidic reaction. Y has a pH value of 8 (>7) and will give an alkaline reaction.


Q.54 Fresh milk has a pH of 6. When it changes into curd, will its pH value increase or decrease? Why?

Usually, fresh milk has a pH of 6. When fresh milk changes into curd, its pH value decreases because of an increase in the acidity of the milk. Bacteria usually change fresh milk to curd by producing lactic acid. Fresh milk that has changed into curd is sour, because its acidity has increased. Hence, the pH value of fresh milk becomes less than 6 when it changes into curd.


Q.55 (a) what is a universal indicator? For what purpose is it used ?

(b) How does a universal indicator work?

(c) Water is a neutral substance. What colour will you get when you add a few drops of universal indicator to a test-tube containing water?

(a) A universal indicator is a combination of different dyes that show colour change with solution of different pH values on the complete pH scale.

A universal indicator paper is used to differentiate between acids and bases. It also differentiates between strong acids and bases and between weak acids and bases on the bases of the intensity of colour change.

(b) When one or two drops of an acid or a base solution are added to a universal indicator paper, it generates a new colour. By comparing the colour with the pH scale, the pH of the added solution is known. From the pH value, we can identify the strength of the acid or base solution.

(c) A neutral substance has a pH value of 7. When we add a few drops of a universal indicator to a test tube of water (which is a neutral substance), we get a green colour because water is a neutral substance.


Q.56 (a) The pH of cold drink is 5. What will be its action on blue and red litmus solutions?

(b) The pH values of three acids A, B and C having equimolar concentrations are 5,2.8 and 3.5 respectively. Arrange these acids in order of the increasing acid strengths.

(a) The pH value of  cold drink is 5 which is less than 7, so it is acidic. Therefore, blue litmus turns red and red litmus remains as it is.

(b) Acids have a pH value of less than 7. Lower the pH value more will be the strength of acid. Hence, the acids in the increasing order of their strengths are as follows

A < C < B.


Q.57 Under what soil conditions do you think farmer would treat the soil of his fields with quicklime (calcium oxide), or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?

Quicklime, slaked lime and chalk are all bases (pH > 7), and hence, they must be used only in cases where the soil is too acidic (pH < 7). They help in neutralizing the acidity of the soil and assist in bringing the pH closer to 7.


Q.58 (a) What do you think will be the pH in the stomach of a person suffering from indigestion: less than 7 or more than 7?

(b) What do you think will be the pH of an antacid solution: less than 7 or more than 7?

(c) How does an antacid work?

(d) Name two common antacids.

(a) The pH in the stomach of a person suffering from indigestion would be less than 7, because of excess acid generation in the stomach.

(b) The pH of an antacid solution would be greater than 7. Antacids are anti-acids, that is they are bases.

(c) Our stomach produces dilute hydrochloric acid, which helps in the digestion of food. Sometimes excess acid is produced in the stomach, overeating being one of the causes. This results in indigestion along with plain. For relief, antacids which are weak bases and neutralize the excess acid, are taken.

(d) Two common antacids are magnesium hydroxide (also called milk of magnesia) and sodium hydrogen carbonate (also called baking soda).


Q.59 (a) What effect does the concentration of H+ (aq) ions have on the nature of a solution?

(b) What effect does the concentration of OH- ions have on the nature of a solution?

(c) Someone put some universal indicator paper into vinegar. The pH is 3. What does this tell you about the vinegar?

(d) Someone put some universal indicator paper into wet soap. The pH is 8. What does this tell you about the soap?

(a) Acids furnish hydrogen ions (H+ ions) when dissolved in water. The more will be the concentration of H+ ions in a solution, the lower will be its pH. Thus, as increase in the concentration of H+ ions in a solution leads to increase in the acidity of the solution.

(b) Bases furnish hydroxide ions (OH ions) when dissolved in water. The concentration of hydroxide ions increases as bases dissolve in water. With the increase in the concentration of OH ions the pH also increases, thus strengthening the basic nature of the solution.

(c) Universal indicator paper dipped into vinegar shows pH 3, indicating that vinegar is an acid. Acids show a value below 7 on the pH scale.

(d) When Universal indicator paper put into wet soap shows pH 8, it indicates that wet soap is a base.


Q.60 What types of indicator is a Red cabbage? Explain how it works as an indicator?

Red cabbage :  Red cabbage is a simple universal indicator.

When we add cabbage juice in different substances of different pH value, their colour get change.

If substance is highly acidic, its colours turn to red. If substance is highly basic, its colour turns to yellow. If substance is neutral in nature, solution remains bluish in colour.


Q.61 Explain the effect of pH on animals and plants?

Effects of pH on Animals and Plants:

pH of acid rain is around 5-6. This is highly acidic. Due to acid rain, acid reaches into oceans, lakes and affects the life of aquatic animals and plants. Some aquatic animals and plants are died due to acid rain and some plants lose lots of their leaves.

To neutralize this acidic behavior of lakes and oceans, calcium carbonate is added into it.


Q.62 While eating food, it happens to spill some curry on your white shirt.  You immediately scrub it with soap. What happens to its yellow colour on scrubbing with soap? Why? What happens to this stain when the shirt is washed with plenty of water?

When it is immediately scrubbed its colour changes from yellow to reddish brown. This happens because soap is basic in nature and the colour of turmeric changes from yellow to reddish brown in basic medium.

When the shirt is washed with plenty of water, the stain turns yellow again.


Q.63 You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

I shall put a red litmus paper turn by turn in each of the three test tubes. The solution which  will turn red litmus paper blue is a basic solution.

Now the blue litmus so obtained can be put in remaining two test tubes one by one , the solution that turns blue litmus red is an acidic solution, while the other one is distilled water.


Q.64 Give reason why dry hydrochloric acid does not change the colour of dry litmus paper?

H+ ion from Hydrochloric acid, cannot ionize to give H ions in absence of water. Acidic property like change in colour of litmus depends on production of H+  ion, hence there is no colour change.


Q.65 A milk man adds a very small amount of baking soda to fresh milk.

(i) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?

(ii) What do you expect to observe when milk comes to boil?

(i) Alkaline medium does not allow milk to turn sour easily.

(ii) When milk comes to boil, there will be more effervescence due to the presence of baking soda.


Q.66 What would be the colour of litmus in a solution of sodium carbonate?

Litmus turns blue in solution of sodium carbonate.

 

SALTS, WATER OF CRYSTALLIZATION, BAKING SODA & WASHING SODA

Q.67 Define the term salt with its various families?

Salts are the ionic compounds which are produced after the neutralization reaction between acid and base.

Family of Salt :

Salts having common acidic or basic radicals are said to belong to same family.

Example :

• Sodium chloride (NaCl) and Calcium chloride (CaCl2) belong  chloride family

• Sodium sulphate (Na2SO4), Potassim sulphate (K2SO4) and Aluminium sulphate (Al2(SO4)3) belong to sulphate family

• Calcium chloride (CaCl2) and calcium sulphate (CaSO4) belong to calcium family.

• Zinc chloride (ZnCl2) and Zinc sulphate (ZnSO4) belong to zinc family.


Q.68 Explain the causes of formation of acidic, basic and neutral salts?

Cause of formation of acidic, basic and neutral salt :

• When equally strong acid and base react they fully neutralize each other. Due to this a neutral salt is formed in this case.

• When a strong acid reacts with a weak base, the base is unable to fully neutralize the acid. Due to this an acidic salt is formed in this case.

• When a strong base reacts with a weak acid, the acid is unable to fully neutralize the base. Due to this a basic salt is formed in this case.


Q.69 Why there is a colour difference between  CuSO4.H2O and  CuSO4 ?

CuSO4.H2O has a blue colour.The blue colour is due to the presence of water molecules in the structure. The colour of a salt crystal is usually given by the water of crystallisation.

But anhydrous salts (without the water molecules) lose their colour and shape and become white. Thus, CuSO4, which does not have water molecules, appear white.


Q.70 Write the chemical name and formula of (a) common salt, and (b) caustic soda?

(a) The chemical name of common salt is sodium chloride, its formula is NaCl.

(b) The chemical name of caustic soda is sodium hydroxide, its formula is NaOH.


Q.71 What are the two main ways in which common salt occurs in nature?

- Common salts occurs naturally in sea water in the dissolved form.

- Common salt is found in underground deposits as rock salt.


Q.72 Name the major salt present in sea-water?

Common salt (or sodium people) is present naturally in sea water in the dissolved form. This is the major salt present in sea water.


Q.73 How is common salt obtained from sea-water?

Common salt is obtained from sea water by the process of evaporation through the sun's heat, which leaves behind crude common salt. Crude salt is further purified to remove impurities as it has some other salts mixed with it.


Q.74 Why is sodium chloride required in our body?

Sodium chloride is required in our body for the functioning of our nervous system, the movement of muscles, the production of hydrochloric acid in the stomach for digestion of food and various other biochemical processes which occur in our body.


Q.75 Give any two uses of common salt?

Two uses of common salt are as follows:

1. It is used in the manufacturing of soap.

2. It is used to melt ice that collects on the roads in cold countries during winter.


Q.76 The electrolysis of an aqueous solution of sodium chloride gives us three products. Name them?

Three products obtained by the electrolysis of an aqueous solution of sodium chloride are:

1. chlorine gas (formed at the anode)

2. hydrogen gas (formed at the cathode)

3. sodium hydroxide solution (formed near the cathode).


Q.77 During the electrolysis of a saturated solution of sodium chloride, where is:

(a) Chlorine formed?

(b) Hydrogen formed?

(c) Sodium hydroxide formed?

During the electrolysis of a saturated solution of sodium chloride:

(a) Chlorine gas is produced at the anode (positive electrode)

(b) hydrogen gas is produced at the cathode (negative electrode).

(c) sodium hydroxide solution is produced near the cathode.


Q.78 Write down the characteristics of salt?

Characteristics of salt :

• Most of the salts are crystalline solid

• Salts may be transparent or opaque.

• Most of the salts are soluble in water.

• Solution of salts conducts electricity. Salts conduct electricity in their molten state also.

• The salt may be salty, sour, sweet, bitter and savory.

• Neutral salts are odourless.

• Salt can be colourless or of coloured.


Q.79  Define acidic salt with example?

Acidic salt :

Salts which are formed after the reaction between a strong acid and weak base are called acidic salt. The pH value of acidic salt is lower than 7.

Examples of such type of salts are ammonium sulphate, ammonium chloride, etc.

Ammonium chloride (NH4Cl) is formed after reaction between hydrochloric acid (a strong acid) and ammonium hydroxide (a weak base).


Q.80 Define neutral salt with example?

Neutral Salt :

Salts produced because of reaction between strong acid and strong base are neutral in nature. The pH value of such salts is equal to 7, i.e. neutral.

Examples of such type of salts are sodium chloride, sodium sulphate, potassium chloride, etc.

Sodium chloride (NaCl) is formed after the reaction between hydrochloric acid

(a strong acid).

NaOH + HCl \to NaCl + {H_2}O


Q.81 Explain method of obtaining common salt?

Methods of obtaining Sodium Chloride :

(a)From sea water by evaporation : Spread sea water in open. In summer season, water of seawater evaporates in atmosphere and we get sodium chloride.

(b)From rock salt found in mines : Sodium chloride is mined from deposits which form underground. Deposits of rock salt are usually the remains of inland seas which evaporated thousands or millions of year ago.


Q.82 What is a basic salt? Explain with example?

Salts which are formed after the reaction between weak acid and strong base are called basic salt. The pH value of acidic salt is greater than 7.

Examples of such types of salts are sodium carbonate, sodium acetate, etc.

Sodium carbonate (Na2CO3) is formed after reaction between sodium hydroxide (a strong base) and carbonic acid (a weak base).


Q.83 Define common salt; discuss its pH value and Uses?

Common Salt (Sodium Chloride) :

Sodium chloride (NaCl) is also known as a common salt or table salt. It is formed after the reaction between sodium hydroxide and hydrochloric acid.

NaOH + HCl → NaCl

• It is a neutral salt.

• The pH value of sodium chloride is about 7.

• Sodium chloride is used in cooking as well as to prepare many other important chemicals such as chemicals used in manufacturing industries.


Q.84 Explain the electrolysis process of Brine and name the process?

Electrolysis process of brine :

• Sodium hydroxide is a strong base. It is also known as caustic soda or lye.

• It is obtained by the electrolytic decomposition of solution of sodium chloride (brine).

• In the process of electrolytic decomposition of brine (aqueous solution of sodium chloride), brine decomposes to form sodium hydroxide.

• In this process, chlorine is obtained at anode and hydrogen gas is obtained at cathode as byproducts. This whole process is known as Chlor-Alkali process.


Q.85 Write down the uses of products after electrolysis of brine?

Use of product after the electrolysis of brine :

• Hydrogen gas is used as fuel, margarine, in making of ammonia for fertilizer, etc.

• Chlorine gas is used in water treatment, manufacturing of PVC, disinfectants, CFC, pesticides. It is also used in manufacturing of bleaching powder and hydrogen acid.

• Sodium hydroxide is used in de-greasing of metals, manufacturing of paper, soap, detergents, artificial fibers, bleach, etc.


Q.86 What is the chemical formula of (a) baking soda (b) washing soda?

(a) The chemical formula of baking soda is NaHCO its chemical name is sodium hydrogen carbonate

(b) The chemical formula of washing soda is Na2CO3.10H2O its chemical name is sodium carbonate decahydrate.


Q.87 Write the chemical formula of (a) soda ash and (b) washing soda?

(i) The chemical formula of soda ash is Na2CO2.  Its chemical name is sodium carbonate.

(ii) The chemical formula of washing soda is Na2CO3H2O. Its chemical name is sodium carbonate decahydrate.


Q.88 Name the product formed when Cl2 and H2  produced, during the electrolysis of brine ?

When hydrogen and chlorine react with each other, hydrochloric acid (HCl) is formed

H2 + Cl2 → 2HCl


Q.89 Name an acid which is present in baking  powder?

Tartaric acid is present in baking powder. Baking powder is a mixture of tartaric acid and sodium hydrogen carbonate.


Q.90 Write down the uses of sodium carbonate?

Uses of sodium carbonate :

• It is used in cleaning of cloths; especially in rural area.

• In making of detergent cake and powder

• In removing permanent hardness of water

• It is used in glass and paper industries.


Q.91 Explain solvay process?

Sodium carbonate is manufactured by the thermal decomposition of sodium hydrogen carbonate obtained by Solvay process. 

NaCl + C{O_2} + N{H_3} + {H_2}O \to N{H_4}Cl + NaHC{O_3} 

          

The sodium carbonate obtained in this process is dry. It is called soda ash or anhydrous sodium carbonate. Washing soda is obtained by rehydration of anhydrous sodium carbonate.


Q.92 Write the formula of sodium chloride and sodium carbonate. Explain why an aqueous solution of sodium chloride is neutral but an aqueous of sodium carbonate is basic. Write chemical equations of the reactions involved?

The formula of sodium chloride is NaCl and that of sodium carbonate is Na2CO3 an aqueous solution of sodium chloride is neutral because sodium chloride is formed from a strong acid, hydrochloric acid, and a strong base, sodium hydroxide (NaOH). When sodium chloride is dissolved in water. It gets hydrolysed to give equal amoutns of hydroxide and hydrogen ions and this makes its aqueous solution neutral.

NaCl(s) + H2O(l) → NaOH(aq) + HCl(aq)

An aqueous solution of sodium carbonate (washing soda) is alkaline because it is a salt prepared from the reaction of a weak acid, carbonic acid (H2CO3), and a strong base, sodium hydroxide (NaOH). When sodium carbonate is dissolved in water, it gets hydrolysed to some extent and form sodium hydroxide and carbonic acid.

Na2CO3(s) + 2H2O(aq) → 2NaOH(aq) + H2CO3(aq)

Sodium hydroxide, being a strong base, is fully ionised to give a large amount of hydroxide ions (OH), and carbonic acid, being a weak acid, is slightly ionised to form a small amount of hydrogen (H+) ions. Therefore, an aqueous solution contains more hydroxide ions than hydrogen ions and this makes the solution basic.


Q.93 Give the important uses of baking soda. How does baking soda differ chemically from washing soda?

Uses of baking soda

• Baking soda is used in making of baking powder, which is used in cooking as it produces carbon dioxide which makes the batter soft and spongy.

• Baking soda is used as antacid

• Baking soda is used in toothpaste which makes the teeth white and plaque free.

• Baking soda is used in cleansing of ornaments made of sliver.

• Since, sodium hydrogen carbonate gives carbon dioxide and sodium oxide on strong heating, thus it is used as fire extinguisher.

Washing soda, or sodium carbonate (Na2CO3.10H2O), consists of two sodium attached to a carbonate group with 10 molecules of water of crystallisation, whereas baking soda comprises one atom of sodium and one of hydrogen, attached to a carbonate group. Hence, baking soda (NaHCO3) differs from washing soda (Na2CO3) by one hydrogen atom. When baking soda is heated up at high temperature, it breaks down to form sodium carbonate, water vapour and carbon dioxide.


Q.94 (a) What is meant by “water of crystallization in a substance? Explain with an example.

(b) How would you show that blue sulphate crystals contain water of crystallization?

(c) Explain how anhydrous copper sulphate can be used to detect the presence of moisture in a liquid.

(a) Water of crystallization :

Many salts contain water molecule and are known as hydrated salts. The water molecules presents in salt is known as water of crystallization. For example : copper sulphate pentahydrate (CuSO4.5H2O), ferrous Sulphate heptahydrate (FeSO4.7H2O), Plaster of Paris etc.

(b) When copper sulphate crystals (chemical formula CuSO45H2O) are heated strongly, they lose all the water of crystallisation and form anhydrous copper sulphate (CuSO4), which is white. As the blue colour of the crystals disappeared on heating, we can conclude that the colour was due to water of crystallisation. This proves that blue copper sulphate crystals contain water of crystallisation.

CuSO4.5H2O  → CuSO4 + 5H2O

(c) A few drops of the liquid to be tested are added to white anhydrous copper sulphate powder. The appearance of a blue colour in anhydrous copper sulphate indicates the presence of moisture or water in the liquid.


Q.95 (a) what will happen if heating is not controlled while preparing plaster of paris?

(b) write an equation to show the reaction between plaster of paris and water? 

(a) If heating is not controlled while preparing plaster of Paris, then all its water of crystallisation is eliminated and anhydrous calcium sulphate (CaSO4), called dead burnt plaster, is formed. The anhydrous calcium sulphate does not set like plaster of Paris on addition of water.

(b) CaS{O_4}.{1 \over 2}{H_2}O + 1{1 \over 2}{H_2}O \to CaS{O_4}.2{H_2}O


Q.96 (a) What is the chemical name of bleaching powder?

(b) What is the chemical formula of bleaching powder?

(c) What are the materials used for the preparation of bleaching powder?

(d) State one use of bleaching powder?

(a) The chemical name of bleaching powder is calcium oxychloride.

(b) The chemical formula of bleaching powder is CaOCl2

(c) The substances used for the preparation of bleaching powder are chlorine (Cl2) and slaked like Ca(OH)2].

(d) Bleaching powder is used as a disinfectant. It is used for making water free from germs.


Q.97 (a) What is gypsum? What happens when gypsum is heated to 1000 C ?

(b) Name a sodium compound which is used for making borax and glass?

(c) Name the compound which is used in hospitals for setting fractured bones?

(d)  Which is the real bleaching agent present in bleaching powder?

(a) Gypsum is calcium sulphate dihydrate (CaSO4.2H2O). When gypsum is heated to a temperature of 100°C (373K), it loses three-fourths of its water of crystallisation and forms plaster of Paris (CaSO4.1/2H2O).

(b) Sodium carbonate or washing soda is used for making borax and glass.

(c) Plaster of Paris sets into a hard mass on addition of water. It is easy to mould a layer Plaster of Paris around the damaged part, which later solidifies and provides support to the damaged bone for its quick healing. This is why it is used in hospitals for setting fractured bones.

(d)  Chlorine is the real bleaching agent present in bleaching powder.


Q.98 (a) What is “ baking powder” ? How does it make the cake soft and spongy?

(b) In addition to sodium hydrogencarbonate, baking powders contain a substance X. Name the substance X. What is the role of substance X in the baking powder?

(a) Baking powder is a sodium salt called sodium bicarbonate (NaHCO3). It is a mixture of baking soda (sodium hydrogen carbonate) and a mild edible acid such as tataric acid. When baking soda mixes with water, the sodium hydrogencarbonate reacts with the tartaric acid to produce carbon dioxide gas. The carbon dioxide as produced gets tapped in the wet dough made for baking a cake or bread and bubbles out slowly and the cake or bread becomes soft and spongy.

(b) In addition to sodium hydrogencarbonate, baking powder contains tartaric acid (X). Tartaric acid is added to baking powder to neutralise the bitter taste that baking soda produces in the cake. Also, carbon dioxide, which makes the cake fluffy and soft, is produced only when the tartaric acid reacts with the sodium hydrogencarbonate r baking soda, in the presence of water.


Q.99 (a) What is the common name of the compound CaOCl2?

(b) Name the raw material used for the preparation of plaster of paris.

(c) Which property of plaster of paris is utilized in making casts for broken limbs in hospitals?

(d) Explain why chlorine is used for sterling drinking water supply?

(a) The common name of the compound CaOCl2 is bleaching powder.

(b) The raw material used for the preparation of plaster of Paris is gypsum (CaSO4/2H2O).

(c) Plaster of Paris has a property of setting into a hard mass in about half an hour after wetting with water. This property is utilised in making casts for broken limbs in hospitals.

(d) Chlorine is a disinfectant used for sterilising drinking water supply in order to kill disease-causing bacteria that the water or water pipes might contain.

 

Value Based Questions :- 

Q.1 A person found that the cake prepared by him is hard and small in size. Which in gradient has he forgotten to add that would have caused the cake to rise and become light? Explain your answer.

The person forgot to add baking powder

Baking powder is a mixture of baking soda (sodium hydrogencarbonate) and a mild edible acid such as tartaric acid.

When baking powder mixes with water, the sodium hydrogen carbonate reacts with the tartaric acid to emit carbon dioxide gas. The carbon dioxide gas produced gets trapped in the wet dough made for baking a cake or bread, and bubbles out slowly. Thus, the cake becomes soft and spongy.


Q.2 Rohan has been stung by a honey –bee and is in great pain. What could be the reason for this burning pain? State the type of chemical compound that can be applied on the affected area to give relief to Rohan?

The reason for this burning pain is methanoic acid which is injected by a honey-bee. A mild base like baking soda can be applied on the affected area to give relief.


Q.3 Ajay likes to eat a lot chocolates. His sister Anita asks him to brush his teeth before going to sleep in the night everyday. Ajay says brushing the teeth in the morning is enough.

(i) Who is correct? Why? Justify.

(ii) What is the value displayed by Anita?

(i) Anita is correct. The sugar and food particles left in between the teeth are acted upon by bacteria present in the mouth which break them into acids. These acids damage teeth by corroding them.

Tooth paste not only helps in removing these food particles but also neutralises the excess of acid formed because it is basic in nature.

(ii) Anita understands the harm of not keeping one’s teeth clean. She is aware of the action of bacteria in mouth and the properties of the tooth paste.



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