Acids, Bases and Salts Selina Concise Chemistry Class 10

Selina Concise Chemistry Class 10 Acids, Bases and Salts.

Exercise Intext 1

1.(a) What do you understand by the term, acid?

(b) Name the positive ion formed when an acid is dissolved in water.

(c) Draw the structure of this ion.

Solution 1.

(a) Acids are defined as compounds which contain one or more hydrogen atoms, and when dissolved in water, they produce hydronium ions (H3O+), the only positively charged ions.

(b) Hydronium ion
(c) H3O+

2.Write the ionisation reaction of sulphuric acid showing the formation of hydronium ion.

Solution 2.

H2SO4 + H2O ⇌ H3O+ + HSO4-
HSO4- + H2O ⇌ H3O+ + SO4-2

3.Water is never added to acid in order to dilute it. Why?

Solution 3.

If water is added to a concentrated acid, the heat generated causes the mixture to splash out and cause severe burns. Thus, water is never added to acid in order to dilute it.

4.Define the term 'basicity' of an acid. Give the basicity of: nitric acid, sulphuric acid, phosphoric acid?

Solution 4.

Basicity: The basicity of an acid is defined as the number of hydronium ions (H3O+) that can be produced by the ionization of one molecule of that acid in aqueous solution.

The basicity of following compounds are:

Nitric acid: Basicity= 1
Sulphuric acid: Basicity=2
Phosphoric acid: Basicity=3

5.Give two examples of each of the following:

(a) Oxy-acid

(b) Hydracid

(c) Tribasic acid

(d) Dibasic acid

Solution 5.

(a) Oxyacids: – HNO3, H2SO4
(b) Hydracid:- HCl, HBr
(c) Tribasic acid:- H3PO4, H3PO3
(d) Dibasic acid: – H2SO4 , H2CO3

6.Name the

(a) acidic anhydride of the following acids:

(i) Sulphurous acid

(ii) Nitric acid

(iii) Phosphoric acid

(iv) Carbonic acid

(b) Acids present in vinegar, grapes and lemon?

(c)

Solution 6.

(a) The anhydride of following acids are:

1. Sulphurous acid: SO2
2. Nitric acid: N2O5
3. Phosphoric acid: P2O5
4. Carbonic acid : CO2

(b) Acids present in following are:
Vinegar: Acetic acid
Grapes: Tartaric acid and Malic acid
Lemon: Citric acid

(c)

1. H+ ion turns blue litmus red.
2. OH– ion turns red litmus blue.

7.What do you understand by the statement 'acetic acid is a monobasic' acid?

Solution 7.

Acetic acid is a monobasic acid which on ionization in water produce one hydronium ion per molecule of the acid.

8.Give a balanced equation for reaction of nitrogen dioxide with water 

Solution 8.

2NO2(g) + H2O(l)→ HNO2(aq) + HNO3

9.What do you understand by the strength of acid? On which factors does the strength of an acid depend?


Solution 9.

The strength of an acid is the extent to which the acid ionizes or dissociates in water. The strength of an acid depends on the degree of ionization and concentration of hydronium ions [H3O+] produced by that acid in aqueous solution.

10.Explain the following:

(a)Carbonic acid gives an acid salt but hydrochloric acid does not. Explain.

(b) Dil. HCl acid is stronger than highly concentrated acetic acid. Explain.

(c) H₃PO₃ is not a tribasic acid.

(d) Lead carbonate does not react with dilute HCl.

(e) Nitrogen dioxide is a double acid anhydride.

Solution 10.

(a) Carbonic acid is a dibasic acid with two replaceable hydrogen ions; therefore it forms one acid salt or one normal salt. Hydrochloric acid is a monobasic acid with one replaceable hydrogen ion and so forms only one normal salt.

(b) Strength of an acid is the measure of concentration of hydronium ions it produces in its aqueous solution. Dil. HCl produces high concentration of hydronium ion compared to that of concentrated acetic acid. Thus, dil. HCl is stronger acid than highly concentrated acetic acid.

(c) H3PO3 is not a tribasic acid because in oxyacids of phosphorus, hydrogen atoms which are attached to oxygen atoms are replaceable. Hydrogen atoms directly bonded to phosphorus atoms are not replaceable.

(d) The salt produced is insoluble in the solution so the reaction does not proceed. Hence, we do not expect lead carbonate to react with hydrochloric acid.

(e) NO2 is called double acid anhydride because two acids – nitrous acid and nitric acid – are formed when it reacts with water.

2NO2 + H2O → HNO2 + HNO3

11.

Solution 11.

Acid rain is a by-product of a variety of human activities which release oxides of sulphur and nitrogen in the atmosphere. Burning of fossil fuels, coal, oil, petrol and diesel produces sulphur dioxide and nitrogen oxide which pollute the air. Polluted air also contains many oxidising agents which produce oxygen because of excessive heat. This oxygen combines with the oxides of sulphur and nitrogen and rain water to form acids.

2SO2 + O2 + 2H2O → 2H2SO4
4NO2 + O2 + 2H2O → 4HNO3


12.How is an acid prepared from a (a) non-metal (b) salt? Give an equation for each.

Solution 12.

(a) Acids are prepared from non-metals by their oxidation. For example :

Sulphur or phosphorus is oxidized by conc. Nitric acid to form sulphuric acid or phosphoric acid.

(b) Acids are prepared from salt by the displacement reaction. For example :

Nitric acid is prepared by using H2SO4 and sodium chloride.

13.Give an equation to show how the following are made from their corresponding anhydrides.

(a) Sulphurous acid

(b) Phosphoric acid

(c) Carbonic acid

(d) Sulphuric acid

Solution 13.

(a) SO2 +H2O H2SO3
(b) P2O5 +3H2O 2H3PO4
(c) CO2 + H2O H2CO3

14.Name an acid used:

(a) To flavor and preserve food

(b) In a drink

(c) To remove ink spots

(d) As an eyewash

Solution 14.

4(a) Citric acid
(b) Carbonic acid
(c) Oxalic acid
(d) Boric acid

Exercise Intext 2

1.What do you understand by an alkali? Give two examples of :

(a) Strong alkalis

(b) Weak alkalis

Solution 1.

An alkali is a basic hydroxide which when dissolved in water produces hydroxyl ions (OH–) as the only negatively charged ions.
(a) Strong alkalis: Sodium hydroxide , Potassium hydroxide

(b) Weak alkalis: Calcium hydroxide , Ammonium hydroxide

2.What is the difference between :

(a) An alkali and a base

(b) The chemical nature of an aqueous solution of HCl and an aqueous solution of NH₃

Solution 2.

(a) An alkali and a base:
1. Alkalis are soluble in water whereas bases may be or may not be soluble in water.
2. All alkalis are bases but all bases are not alkalis.

(b) The chemical nature of an aqueous solution of HCl and an aqueous solution of NH3

1. The aqueoussolution of HCl is acidic in nature. It can turn blue litmus to red.
2. The aqueoussolution of NH3 is basic in nature. It can turn red litmus to blue.

3.Name the ions furnished by

a. bases in solution

b. an acid

Solution 3.

(a) Hydroxyl ion (OH–)
(b)  H+

4.Give one example in each case:

(a) A basic oxide which is soluble in water,

(b) A hydroxide which is highly soluble in water,

(c) A basic oxide which is insoluble in water,

(d) A hydroxide which is insoluble in water,

(e) A weak mineral acid,

(f) A base which is not an alkali,

(g) An oxide which is a base,

(h) A hydrogen containing compound which is not an acid,

(i) A base which does not contain a metal ion.

Solution 4.

(a) Barium oxide
(b) Sodium hydroxide
(c) Manganese oxide
(d) Cupper hydroxide
(e) Carbonic acid
(f) Ferric hydroxide
(g) Copper oxide
(h) Ammonia
(i) Ammonium hydroxide

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

Solution 5.

The test tube containing distilled water does not affect the red litmus paper.
The test tube containing acidic solution does not change the red litmus paper.

But the test tube containing basic solution turns red litmus paper blue.

6.HCl, HNO₃, C₂H₅OH, C₆H₁₂O₆ all contain H atoms but only HCl and HNO₃ show acidic character. Why?

Solution 6.

It is because HCl and HNO3 ionize in aqueous solution whereas ethanol and glucose do not ionize in aqueous solution.

7.a. Dry HCl gas does not change the colour of dry litmus paper. Why?

b. ls PbO₂ a base or not? Comment.

c. Do basic solutions also have H⁺_(aq)? Explain why they are basic by taking an example ?

Solution 7.

(a) DryHCl gas does not contain any hydrogen ions in it, so it does not show acidic behaviour. Hence, dry HCl gas does not change the colour of dry litmus paper.

(b) Lead oxide is a metallic oxide which reacts with hydrochloric acid to produce lead chloride and water, but it is excluded from the class of bases, because chlorine is also produced.

PbO2 + 4HCl → PbCl2 + Cl2 + 2H2O

Thus, lead oxide is not a base.

(c)Yes, basic solutions have H+ions, but the concentration of OH– ions is more than the H+ ions which makes the solution basic in nature.

8.How would you obtain:

(a) A base from other base

(b) An alkali from a base

(c) Salt from another salt?

Solution 8.

(a) We can obtain a base from another base by double decomposition. The aqueous solution of salts with base precipitates the respective metallic hydroxide.

FeCl3 +3NaOH   Fe(OH)3 +3NaCl

(b) An alkali from a base

(c) Salt from another salt

9.Write balanced equations to satisfy each statement.

(a) Acid + Active metal Salt + Hydrogen

(b) Acid + base Salt + Water

(c) Acid + Carbonate orbicarbonate Salt + Water + carbon dioxide

(d) Acid + sulphite or bisulphite salt + water + sulphur dioxide

(e) Acid + Sulphide Salt + hydrogen sulphide

Solution 9.

(a) Mg +2HCl MgCl2 + H2
(b) HCl + NaOH NaCl + H2O
(c) CaCO3 +2HCl CaCl2 +H2O + CO2
(d) CaSO3 + 2HCl CaCl2 + H2O+ SO2
(e) ZnS + 2HCl ZnCl2 + H2S

10.The skin has and needs natural oils. Why is it advisable to wear gloves while working with strong alkalis?

Solution 10.

As we know that alkalis react with oil to form soap. As our skin contains oil so when we touch strong alkalis, a reaction takes place and soapy solution is formed. Hence we should wear gloves.

11.Complete the table:

Indicator	Neutral	Acidic	Alkaline
Litmus Phenolphthalein	Purple Colourless

Solution 11.

12.What do you understand by pH value? Two solutions X and Y have pH values of 4 and 10, respectively. Which one of these two will give a pink colour with phenolphthalein indicator?

Solution 12.

pH represents the strength of acids and alkalis expressed in terms of hydrogen ion concentration. The solution with pH value 10 will give pink colour with phenolphthalein indicator.

13.You are supplied with five solutions : A , B , C , D and E with pH values as follows:

A =1.8 , B=7 , C=8.5 , D=13 and E=5

Classify these solutions as neutral, slightly or strongly acidic and slightly or strongly alkaline.

Which solution would be most likely to liberate hydrogen with:

(a) Magnesium powder

(b) Powered zinc metal. Give a word equation for each reaction.

Solution 13.

A = Strongly acidic
B= neutral
C=Weakly alkaline
D= Strongly alkaline
E= Weakly acidic
(a) Solution A (acidic solution) + MgH2 + Mg salt
(b) SolutionA (acidic solution) + ZnH2 + Zn salt

14.Distinguish between :

(a) A common acid-base indicator and a universal indicator

(b) The acidity of bases and basicity of acids

(c) Acid and alkali (other than indicators)

Solution 14.

(a) A common acid-base indicator and a universal indicator:

An acid-base indicator like litmus tells us only whether a given substance is an acid or a base. The universal indicator gives an idea as to how acidic or basic a substance is universal indicator gives different colours with solutions of different pH values.

(b) The acidity of bases and basicity of acids

The acidity of bases: The number of hydroxyl ions which can be produced per molecule of the base in aqueous solution.

Basicity of acid: The basicity of an acid is defined as the number of hydronium ions that can be produced by the ionization of one molecule of that acid in aqueous solution.

(c) Acid and alkali:

An acid is that substance which gives H+ ions when dissolved in water.

An alkali is that substance which gives OH– ions when dissolved in water.

15.How does tooth enamel get damaged? What should be done to prevent it?

Solution 15.

Substances like chocolates and sweets are degraded by bacteria present in our mouth. When the pH falls to 5.5 tooth decay starts. Tooth enamel is the hardest substance in our body and it gets corroded. The saliva produced by salivary glands is slightly alkaline, it helps to increase the pH, to some extent, but toothpaste which contains basic substance is used to neutralize excess acid in the mouth.

16.When you use universal indicator, you see that solutions of different acids produce different colours. Indeed, solution of the same acid with different concentrations will also give different colours. Why?

Solution 16.

A universal indicator is a mixture of dyes which identify a gradual change of various colours over a wide range of pH, depending on the strength of the acid. When we use a universal indicator, we see solutions of different acids produce different colours. Indeed, solutions of the same acid with different concentration give different colours.

The more acidic solutions turn universal indicator bright red. A less acidic solution will only turn it orange-yellow. Colour differences can also be observed in case of vinegar which is less acidic and battery acid which is more acidic.

17.a. A solution has a pH of 7. Explain how you would 

 i. increase its pH

 ii. decrease its pH

b. If a solution changes the colour of litmus from red to blue, what can you say about its pH?

c. What can you say about the pH of a solution that liberates carbon dioxide from sodium carbonate?

Solution 17.

(a)
1. The pH can be increased by adding a basic solution.
2. The pH can be increased by adding an acidic solution.
(b) The solution is basic in nature and the pH value will be more than 7.
(c)Less than 7

18.Solution P has a pH of 13, solution Q has a pH of 6 and solution R has a pH of 2.

Which solution

a.  will liberate ammonia from ammonium sulphate on heating?

b.  is a strong acid?

c.  contains molecules as well as ions?

Solution 18.

(a) Solution P
(b) Solution R
(c)Solution Q

Exercise Intext 3

1.Define the following and give two examples in each case:

 (a) a normal salt, (b) an acid salt, (c) a mixed salt.

Solution 1.

(a) A normal salt: Normal salts are the salts formed by the complete replacement of the ionizable hydrogen atoms of an acid by a metallic or an ammonium ion.

(b) An acidic salt: Acid salts are formed by the partial replacement of the ionizable hydrogen atoms of a polybasic acid by a metal or an ammonium ion.

(c) A mixed salt: Mixed salts are those salts that contain more than one basic or acid radical.
Examples:
(a) A Normal salt: Na2SO4 , NaCl
(b) An acid salt: ANaHSO4 , Na2HPO4
(c) A mixed salt: NaKCO3 , CaOCl2

2.Answer the following questions related to salts and their preparations:

(a) What is a salt?

(b) What kind of salt is prepared by precipitation?

(c) Name a salt prepared by the direct combination. Write an equation for the reaction that takes place in preparing the salt you have named.

(d) Name the procedure used to prepare a sodium salt such as sodium sulphate.

Solution 2.

(a) Salt is a compound formed by the partial or total replacement of the ionizable hydrogen atoms of an acid by a metallic ion or an ammonium ion.

(b) An insoluble salt can be prepared by precipitation.
(c) A salt prepared by direct combination is Iron(III) chloride.
Reaction:
2Fe +3Cl2 2FeCl3
(d) By neutralizing sodium carbonate or sodium hydroxide with dilute sulphuric acid:
Na2CO3 + H2SO4 → Na2SO4 + H2O + CO2
2 NaOH + H2SO4 → Na2SO4 + 2H2O

3.Describe giving all practical details , how would you prepare :

(a) Copper sulphate crystals from mixture of charcoal and black copper oxide,

(b) Zinc sulphate crystals from Zinc dust (powered Zinc and Zinc oxide)

(c) sodium hydrogen carbonate crystals

(d) Calcium sulphate from calcium carbonate

Solution 3.

(a) Copper sulphate crystals from a mixture of charcoal and black copper oxide:
The carbon in the charcoal reduces the black copper oxide to reddish-brown copper. The lid must not be removed until the crucible is cool or the hot copper will be re-oxidized by air.

Take dilute sulphuric acid in a beaker and heat it on wire gauze. Add cupric oxide in small quantities at a time, with stirring till no more of it dissolves and the excess compound settles to the bottom.

Filter it hot and collect the filtrate in a china dish. Evaporate the filtrate by heating to the point of crystallization and then allow it to cool and collect the crystals of copper sulphate pentahydrate.

Reaction:
CuO + H2SO4 CuSO4 + H2O
CuSO4 + 5H2O CuSO4. 5H2O
(b) Zinc sulphate crystals from Zinc dust:

Take dilute sulphuric acid in a beaker and heat it on wire gauze. Add some granulated zinc pieces with constant stirring. Add till the Zinc settles at the base of the beaker. Effervescences take place because of the liberation of hydrogen gas. When effervescence stops, it indicates that all the acid has been used up. The excess of zinc is filtered off. Collect the solution in a china dish and evaporate the solution to get crystals. Filter, wash them with water and dry them between the folds of paper. The white needle crystals are of hydrated Zinc sulphate.

Reaction:
Zn + H2SO4 ZnSO4 + H2
ZnSO4 +7 H2O ZnSO4. 7 H2O
(c) Lead sulphate from metallic lead:

Metallic lead is converted to lead oxide by oxidation. Then lead sulphate is prepared from insoluble lead oxide, by first converting it into soluble lead nitrate. Then the lead nitrate solution is treated with sulphuric acid to obtain white ppt. of Lead sulphate.

Reaction:
PbO +2HNO3 Pb(NO3)2 + H2O
Pb(NO3)2 + H2SO4 PbSO4 + 2HNO3
(d)Sodium hydrogen carbonate crystals:

Dissolve 5 grams of anhydrous sodium carbonate in about 25 ml of distilled water in a flask. Cool the solution by keeping the flask in a freezing mixture. Pass carbon dioxide gas in the solution. Crystals of sodium bicarbonate will precipitate out after some time. Filter the crystals and dry it in folds of filter paper.

Reaction:
Na2CO3 + CO2 + H2O 2NaHCO3

4.The following is the list of methods for the preparation of salts.

A-Direct combination of two elements.

B-reaction of dilute acid with a metal.

C-reaction of dilute acid with an insoluble base.

D-Titration of dilute acid with a solution of soluble base.

E- reaction of two solutions of salts to form a precipitate.

Choose from the above list A to E , the best method of preparing the following salts by giving a suitable equation in each case:

1. Anhydrous ferric chloride,

2. Lead chloride,

3. Sodium sulphate,

4. Copper sulphate.

Solution 4.

1. Anhydrous ferric chloride: -A (Direct combination of two elements)
2Fe + 3Cl2 2FeCl3
2. Lead chloride: -E (Reaction of two solutions of salts to form a precipitate)
Pb(NO3)2 +2HCl PbCl2 +2HNO3
3. Sodium sulphate: – D( Titration of dilute acid with a solution of soluble base)
2NaOH + H2SO4 Na2SO4 +2H2O
4. Coppersulphate:– C (reaction of dilute acid with an insoluble base)
Cu(OH)2 +H2SO4 CuSO4 + 2H2O

5.Name:

(a) A chloride which is insoluble in cold water but dissolves in hot water,

(b) A chloride which is insoluble,

(c) Two sulphates which are insoluble,

(d) A basic salt,

(e) An acidic salt,

(f) A mixed salt,

(g) A complex salt,

(h) A double salt,

(i) a salts whose solubility increases with temperature,

(j) A salt whose solubility decreases with temperature.

Solution 5.

(a) Lead chloride
(b) Silver chloride
(c) Barium sulphate and lead sulphate
(d) Basic lead chloride
(e) Sodium hydrogen sulphate
(f) Sodium potassium carbonate
(g) Sodium argentocyanide
(h) Potash alum
(i) Potassium bromide and potassium chloride
(j) Calcium sulphate

6.Fill in the blanks with suitable words:

An acid is a compound which when dissolved in water forms hydronium ions as the only …………… ions. A base is a compound which is soluble in water and contains …………….. ions. A base reacts with an acid to form a …………….. and water only. This type of reaction is known as …………….

Solution 6.

An acid is a compound which when dissolved in water forms hydronium ions as the only positively charged ions. A base is a compound which is soluble in water and contains hydroxide ions. A base reacts with an acid to form a salt and water only. This type of reaction is known as neutralisation.

7.What would you observe when:

(a) Blue litmus is introduced into a solution of hydrogen choride gas.

(b) Red litmus paper is introduced into a solution of ammonia in water

(c) Red litmus paper is introduced in Caustic soda solution?

Solution 7.

(a) Blue litmus will turn into red which will indicate the solution to be acidic.
(b) No change will be observed.
(c) Red litmus will turn into blue will indicate the solution to be basic.

8.Explain why:

(a) It is necessary to find out the ratio of reactants required in the preparation of sodium sulphate.

(b) Fused calcium chloride is used in the preparation of FeCl3.

(c) Anhydrous FeCl3 cannot be prepared by heating hydrated iron (III) chloride.

Solution 8.

(a) Since sodium hydroxide and sulphuric acid are both soluble, an excess of either of them cannot be removed by filtration. Therefore it is necessary to find out on small scale, the ratio of solutions of the two reactants.

(b) As iron chloride is highly deliquescent, so it is kept dry with the help of fused calcium chloride.

(c) On heating the hydrate, HCl acid is released and basic salt (FeOCl) or ferric oxide remains. Hence, anhydrous ferric chloride
cannot be prepared by heating the hydrate.

9.Give the preparation of the salt shown in the left column by matching with the methods given in the right column. Write a balanced equation for each preparation.

SaltMethod of preparation

Zinc SulphatePrecipitation

Ferrous sulphideOxidation

Barium SulphateDisplacement

Ferric sulphateNeutralisation

Sodium sulphateSynthesis

Solution 9.

Zinc Sulphate – Displacement

Ferrous sulphide – synthesis

Barium sulphate – Precipitation

Ferric Sulphate- Oxidation

Sodium sulphate – Neutralisation

10.(a) Give the pH value of pure water. Does it change if common salt is added to it?

(b) Classify the following solutions as acids, bases or salts. Ammonium hydroxide, barium chloride, sodium chloride, sodium hydroxide, H₂SO₄ and HNO₃

Solution 10.

(a) pH of pure water is 7 at 25oC. No, the pH does not change when common salt is added.
(b) Acids: H2SO4 and HNO3
Bases: Ammonium hydroxide and sodium hydroxide.
Salts: Barium chloride and sodium chloride.


11.Define the term neutralization.

(a) Give a reaction, mentioning clearly acid and base used in the reaction.

(b) If one mole of a strong acid reacts with one mole of a strong base, the heat produced is always same. Why?

Solution 11.

Neutralization is the process by which H+ ions of an acid react completely with the [OH]– ions of a base to give salt and water only.

(a)

(b) Neutralization is simply a reaction between H+ ions given by strong acid and OH– ions given by strong base. In case of all

strong acids and strong bases, the number of H+ and OH– ions produced by one mole of a strong acid or strong base is always same. Hence the heat of neutralization of a strong acid with strong base is always same.

12.Write the balanced equation for the preparation of the following salts in the laboratory:

(a) A soluble sulphate by the action of an acid on an insoluble base,

(b) An insoluble salt by the action of an acid on another salt,

(c) An insoluble base by the action of a soluble base on a soluble salt

(d) A soluble sulphate by the action of an acid on a metal.

Solution 12.

13.You are provided with the following chemicals:

NaOH,Na₂CO₃,H₂O,Zn(OH)₂,CO₂,HCl,Fe,H₂SO₄,Cl₂,Zn

Using suitable chemicals from the given list only, state briefly how you would prepare:

(a) Iron(III) chloride,

(b) Sodium sulphate,

(c) Sodium zincate,

(d) Iron(II) sulphate,

(e) Sodium chloride.

Solution 13.

(a) Iron (III) Chloride: Iron chloride is formed by direct combination of elements.

14.For each of the salt: A, B, C and D, suggest a suitable method of its preparation.

a. A is a sodium salt.

b. B is an insoluble salt.

c. C is a soluble salt of copper.

d. D is a soluble salt of zinc.

Solution 14.

(a) By neutralisation:
NaOH + HCl → NaCl + H2O
(b) By precipitation:
Pb(NO3)2 + 2NaCl → PbCl2 + 2NaNO3
(c)CuCO3 + H2SO4→ CuSO4 + H2O + CO2
(d) Simple displacement:
Zn + H2SO4→ ZnSO4 + H2

15.Choosing only substances from the list given in the box below, write equations for the reactions which you would use in the laboratory to obtain:

a. Sodium sulphate

b. Copper sulphate

c. Iron(II) sulphate

d. Zinc carbonate

Dilute sulphuric acid	Copper	Copper carbonate
	Iron	Sodium carbonate
	Sodium
	Zinc

Solution 15.

(a) Na2CO3 + H2SO4 (dil) → Na2SO4 + H2O + CO2
(b) CuCO3 + H2SO4 (dil) → CuSO4 + H2O + CO2
(c) Fe + H2SO4 (dil) → FeSO4 + H2
(d) Zn + H2SO4 (dil) → ZnSO4 + H2
ZnSO4 + Na2CO3 → ZnCO3 + Na2SO4

16.From the formula listed below, choose one, in each case, corresponding to the salt having the given description: AgCl, CuCO₃, CuSO₄.5H₂O, KNO₃, NaCl, NaHSO₄, Pb(NO₃)₂, ZnCO₃, ZnSO₄.7H₂O.

a. an acid salt

b. an insoluble chloride

c. on treating with concentrated sulphuric acid, this salt changes from blue to white

d. on heating, this salt changes from green to black

e. this salt gives nitrogen dioxide on heating

Solution 16.

(a) NaHSO4
(b) AgCl
(c) CuSO4.5H2O
(d) CuCO3
(d) Pb(NO3)2

17.a. Ca(H2PO4)2 is an example of a compound called _______ (acid salt/basic salt/normal salt).

b. Write the balanced equation for the reaction of: A named acid and a named alkali.

Solution 17.

(a) acid salt
(b) NaOH+ HCl → NaCl + H2O

18.State the terms defined by the following sentences:

a. A soluble base.

b. The insoluble solid formed when two solutions are mixed together.

c. An acidic solution in which there is only partial ionisation of the solute molecules.

Solution 18.

(a) Alkali
(b) Precipitate
(c) Weak acid

19.Which of the following methods, A, B, C, D or E is generally used for preparing the chlorides listed below from (i) to (v). Answer by writing down the chloride and the letter pertaining to the corresponding method. Each letter is to be used only once.

A Action of an acid on a metal

B Action of an acid on an oxide or carbonate

C Direct combination

D Neutralisation of an alkali by an acid

E Precipitation (double decomposition)

i. Copper (II) chloride

ii. Iron (II) chloride

iii. Iron (III) chloride

iv. Lead (II) chloride

v. Sodium chloride

Solution 19.

1. Copper (II) chloride – B
2. Iron (II) chloride – A
3. Iron (III) chloride – C
4. Lead (II) chloride – E
5. Sodium chloride – D

20.Complete the following table:

Reactants	Products	Method
Soluble base + Acid (dil)	Salt + water	Neutralisation Titration
Metal + Non-metal	Salt (soluble/insoluble)	……………
Insoluble base +	Salt (soluble) + water	…………….
Active metal + Acid (dil)	………… + …………	…………….
Soluble salt solution (A) +	Precipitated salt +	…………….
Soluble salt solution (B)	Soluble salt	…………….
Carbonate/ bicarbonate + Acid (dil)	Salt + ………. + …………	Decomposition of carbonate
Chlorides/nitrates + Acid (conc)	…………. + …………	Decomposition of chlorides and nitrates

Solution 20.

Exercise Intext 4

1.What do you understand by water of crystallisation?

Give four substances which contain water of crystallisation and write their common names.

Solution 1.

It is the amount of water molecules which enter into loose chemical combination with one molecule of the substance on crystallisation from its aqueous solution.

2.a. Define efflorescence. Give examples.

b. Define deliquescence. Give examples.

Solution 2.

(a) Crystalline hydrated salts which on exposure to the atmosphere lose their water of crystallisation partly or completely and change into a powder. This phenomenon is called efflorescent and the salts are called efflorescent.

Examples: CuSO4.5H2O, MgSO4.7H2O, Na2CO3.10H2O

(b) Water-soluble salts which on exposure to the atmosphere absorb moisture from the atmosphere and dissolve in the same and change into a solution. The phenomenon is called deliquescence and the salts are called deliquescent.

Examples: CaCl2, MgCl2, ZnCl2

3.Distinguish between drying and dehydrating agent.

Solution 3.

4.Explain clearly how conc. H2SO4 is used as a dehydrating as well as a drying agent.

Solution 4.

Conc. sulphuric acid is hygroscopic in nature and can remove moisture from other substances; therefore, it is used as a drying agent. It is also used as a dehydrating agent because it has a strong affinity for water and thus absorbs water quickly from compounds.

5.

Solution 5.

1.  blue
2. red
3. hydrogen gas
4. basic, alkaline
5. graphite

6.Give reasons for the following:

a. Sodium hydrogen sulphate is not an acid, but it dissolves in water to give hydrogen ions according to the equation

 NaHSO₄⇌ H⁺ + Na⁺ + SO₄^2-

b. Anhydrous calcium chloride is used in a desiccator.

Solution 6.

(a) Sodium hydrogensulphate [NaHSO4] is an acid salt and is formed by the partial replacement of the replaceable hydrogen ion in a dibasic acid [H2SO4]. The [H] atom in NaHSO4 makes it behave like an acid.

So, on dissolving in water, it gives hydrogen ions.

(b) Desiccating agentsare used to absorb moisture. Anhydrous calcium chloride (CaCl2) has the capacity of absorbing moisture as it is hygroscopic in nature. So, it is used in a desiccator.

7.State whether a sample of each of the following would increase or decrease in mass if exposed to air.

a. Solid NaOH

b. Solid CaCl₂

c. Solid Na₂CO₃.10H₂O

d. Conc. sulphuric acid

e.  Iron (III) chloride

Solution 7.

(a) Increase
(b) Increase
(c) Decrease
(d) Increase
(e) Increase

8.a. Why does common salt get wet during the rainy season?

b. How can this impurity be removed?

c. Name a substance which changes the blue colour of copper sulphate crystals to white.

d. Name two crystalline substances which do not contain water of crystallisation.

Solution 8.

(a) Table salt turns moist and ultimately forms a solution on exposure to air especially during the rainy season. Although pure sodium chloride is not deliquescent, the commercial version of the salt contains impurities (such as magnesium chloride) which are deliquescent substances.

(b) The impurity can be removed by passing a current of dry hydrogen chloride gas through a saturated solution of the affected salt. Pure sodium chloride is produced as a precipitate which can be recovered by filtering and washing first with a little water and finally with alcohol.

(c) Conc. sulphuric acid

(d) Common salt and sugar

9.Answer the questions below relating your answers only to salts in the following list: Sodium chloride, anhydrous calcium chloride, copper sulphate-5-water?

a. What name is given to the water in the compound copper sulphate-5-water?

b. If copper sulphate-5-water is heated, anhydrous copper sulphate is formed. What is its colour?

c. By what means, other than healing, could you dehydrate copper sulphate-5-water and obtain anhydrous copper sulphate of?

d. Which one of the salts in the given list is deliquescent?

Solution 9.

(a) Water of crystallization
(b) White
(c) By heating with any dehydrating agent
(d) Anhydrous calcium chlorine