SELINA Solutions for Class 10 Chemistry Chapter 3 - Acids, Bases and Salts
Chapter 3 - Acids, Bases and Salts Exercise Ex. 3(A)
What do you understand by an alkali? Give two examples of :
(a) Strong alkalis
(b) Weak alkalis
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
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
(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 aqueous solution of HCl is acidic in nature. It can turn blue litmus to red.
2. The aqueous solution of NH3 is basic in nature. It can turn red litmus to blue.
Name the ions furnished by
a. bases in solution
b. an acid
a. Hydroxyl ion (OH-)
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.
(a) Barium oxide
(b) Sodium hydroxide
(c) Manganese oxide
(d) Cupper hydroxide
(e) Carbonic acid
(f) Ferric hydroxide
(g) Copper oxide
(i) Ammonium hydroxide
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?
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.
HCl, HNO3, C2H5OH, C6H12O6 all contain H atoms but only HCl and HNO3 show acidic character. Why?
It is because HCl and HNO3 ionize in aqueous solution whereas ethanol and glucose do not ionize in aqueous solution.
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 ?
a. Dry HCl 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.
How would you obtain:
(a) A base from other base
(b) An alkali from a base
(c) Salt from another salt?
(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
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
(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
The skin has and needs natural oils. Why is it advisable to wear gloves while working with strong alkalis?
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.
Complete the table:
Blue to red
Red to blue
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?
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.
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.
A = Strongly acidic
D= Strongly alkaline
E= Weakly acidic
(a) Solution A (acidic solution) + MgH2 + Mg salt
(b) SolutionA (acidic solution) + ZnH2 + Zn salt
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)
(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.
What should be added to
(a) Increase the pH value
(b) Decrease the pH value of a neutral solution?
How does tooth enamel get damaged? What should be done to prevent it?
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.
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?
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.
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?
i. The pH can be increased by adding a basic solution.
ii. 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
Solution P has a pH of 13, solution Q has a pH of 6 and solution R has a pH of 2.
a. will liberate ammonia from ammonium sulphate on heating?
b. is a strong acid?
c. contains molecules as well as ions?
a. Solution P
b. Solution R
c. Solution Q
Chapter 3 - Acids, Bases and Salts Exercise Ex. 3(B)
Define the following and give two examples in each case:
(a) a normal salt, (b) an acid salt, (c) a mixed salt.
(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.
(a) A Normal salt: Na2SO4 , NaCl
(b) An acid salt: NaHSO4 , Na2HPO4
(c) A mixed salt: NaKCO3 , CaOCl2
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.
(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.
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
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
(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.
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
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.
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. Copper sulphate:- C (reaction of dilute acid with an insoluble base)
Cu(OH)2 +H2SO4 CuSO4 + 2H2O
(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.
(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
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 …………….
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.
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?
(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.
(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.
(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.
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 Sulphate - Displacement
Ferrous sulphide - synthesis
Barium sulphate - Precipitation
Ferric Sulphate- Oxidation
Sodium sulphate - Neutralisation
(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
(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.
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?
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.
(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.
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.
You are provided with the following chemicals:
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.
(a) Iron (III) Chloride: Iron chloride is formed by direct combination of elements.
(b) Sodium sulphate: By neutralization of caustic soda with dilute sulphuric acid
(c) Sodium zincate: By the action of metals with alkalis
(d) Iron (II) sulphate: Iron sulphate is prepared by the action of dilute acid on an active metal.
(e) Sodium chloride: By the neutralization reaction of strong acid with strong base
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.
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
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
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
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
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.
a. acid salt
b. NaOH + HCl → NaCl + H2O
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.
c. Weak acid
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
i. Copper (II) chloride - B
ii. Iron (II) chloride - A
iii. Iron (III) chloride - C
iv. Lead (II) chloride - E
v. Sodium chloride - D
Complete the following table:
Soluble base + Acid (dil)
Salt + water
Metal + Non-metal
Insoluble base +
Salt (soluble) + water
Active metal + Acid (dil)
………… + …………
Soluble salt solution (A) +
Precipitated salt +
Soluble salt solution (B)
Carbonate/ bicarbonate + Acid (dil)
Salt + ………. + …………
Decomposition of carbonate
Chlorides/nitrates + Acid (conc)
…………. + …………
Decomposition of chlorides and nitrates
Soluble base + Acid (dil)
Salt + water
Metal + Non-metal
Insoluble base +
Salt (soluble) + water
Active metal + Acid (dil)
Salt + Hydrogen
Soluble salt solution (A) + Soluble salt solution (B)
Precipitated salt + Soluble salt
Carbonate /bicarbonate + Acid (dil)
Salt + Water+ Carbon dioxide
Decomposition of carbonate
Chlorides/nitrates + Acid (conc)
Acid salt + HCl/HNO3
Decomposition of chlorides and nitrates
Chapter 3 - Acids, Bases and Salts Exercise Ex. 3(C)
Salts are prepared by the following methods:
(a) Direct combination
(c) Double decomposition (precipitation)
(d) Neutralisation of insoluble base
(e) Neutralisation of an alkali (titration)
(a) Direct combination: Iron(III) chloride
(b) Displacement: ZnSO4
(c) Double decomposition (precipitation): BaSO4
(d) Neutralisation of insoluble base: MgCl2
(e) Neutralisation of an alkali (titration): NaCl
M is an element in the form of a powder. M burns in oxygen and the product obtained is soluble in water. The solution is tested with litmus. Write down only the word which will correctly complete each of the following sentences.
i. If M is a metal, then the litmus will turn _____.
ii. If M is a non-metal, then the litmus will turn _____.
iii. If M is a reactive metal, then _____ will be evolved when M reacts with dilute sulphuric acid.
iv. If M is a metal, it will form _____ oxide, which will form ______ solution with water.
v. If M is a non-metal, it will not conduct electricity in the form of ______.
iii. hydrogen gas
iv. basic, alkaline
What do you understand by water of crystallisation?
Give four substances which contain water of crystallisation and write their common names.
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.
Sodium carbonate decahydrate
Magnesium sulphate heptahydrate
Hydrated potassium aluminium sulphate
Hydrated calcium sulphate
a. Define efflorescence. Give examples.
b. Define deliquescence. Give examples.
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
Distinguish between drying and dehydrating agent.
They remove moisture from other substances.
They remove chemically combined elements of water in the ratio of 2:1 (hydrogen:oxygen) from a compound.
They are used to dry gases like chlorine, sulphur dioxide and hydrogen chloride. They are also used in dessicators to keep substances dry.
They prepare substances such as carbon monoxide and sugar charcoal.
They represent a physical change.
They represent a chemical change.
Explain clearly how conc. H2SO4 is used as a dehydrating as well as a drying agent.
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.
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+ + SO42-
b. Anhydrous calcium chloride is used in a desiccator.
a. Sodium hydrogen sulphate [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 agents are 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.
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
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.
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
Name the salt which on hydrolysis forms
(b) Basic acid
(c) Neutral solution. Give a balanced equation for each reaction.
(a) Iron chloride(FeCl3)
FeCl3 + 3H2O → 3HCl + Fe(OH)3
(b) Ammonium acetate (CH3COONH4)
CH3COONH4 +H2O → CH3COOH + NH4OH
(c) Sodium chloride
NaCl(s) + H2O → Na+(aq) OH-(aq) + H2O
State the change noticed when blue litmus and red litmus are introduced in the following solutions:
(a) Na2CO3 solution
(b) NaCl solution
(d) MgCl2 Solution
(a) Na2CO3 solution: This solution is alkaline in nature; hence, red litmus changes to blue.
(b) NaCl solution: There is no change in the colour of the litmus paper because this solution is neutral.
(c) NH4NO3: This solution is alkaline in nature; hence, red litmus changes to blue.
(d) MgCl2: It is slightly acidic and neutral; hence, there is no change in the litmus paper.
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?
d. Which one of the salts in the given list is deliquescent?
a. Water of crystallization
c. By heating with any dehydrating agent
d. Anhydrous calcium chloride
State your observation when
(a) Washing soda crystals
(b) Iron (III) chloride salts are exposed to the atmosphere.
(a) When washing soda (Na2CO3.10H2O) is exposed to air, it loses 9 molecules of water to form a monohydrate.
(b) It absorbs moisture from the atmosphere and becomes moist and ultimately dissolves in the absorbed water, forming a saturated solution.
Chapter 3 - Acids, Bases and Salts Exercise Intext 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.
(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
Write the ionisation reaction of sulphuric acid showing the formation of hydronium ion.
H2SO4 + H2O ⇌ H3O+ + HSO4-
HSO4- + H2O ⇌ H3O+ + SO4-2
Water is never added to acid in order to dilute it. Why?
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.
Define the term 'basicity' of an acid. Give the basicity of: nitric acid, sulphuric acid, phosphoric acid?
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
Give two examples of each of the following:
(c) Tribasic acid
(d) Dibasic acid
(a) Oxyacids: - HNO3, H2SO4
(b) Hydracid:- HCl, HBr
(c) Tribasic acid:- H3PO4, H3PO3
(d) Dibasic acid: - H2SO4 , H2CO3
(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?
(a) The anhydride of following acids are:
(i) Sulphurous acid: SO2
(ii) Nitric acid: N2O5
(iii) Phosphoric acid: P2O5
(iv) Carbonic acid: CO2
(b) Acids present in following are:
Vinegar: Acetic acid
Grapes: Tartaric acid and Malic acid
Lemon: Citric acid
What do you understand by the statement 'acetic acid is a monobasic' acid?
Acetic acid is a monobasic acid which on ionization in water produce one hydronium ion per molecule of the acid.
Give a balanced equation for (i) reaction of nitrogen dioxide with water (ii) Preparation of non-volatile acid from a volatile acid.
(i) 2NO2(g) + H2O(l)→ HNO2(aq) + HNO3
(ii) H2S2O7 + H2O → 2 H2SO4
What do you understand by the strength of acid? On which factors does the strength of an acid depend?
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.
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.
(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
How is an acid prepared from a (a) non-metal (b) salt? Give an equation for each.
(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.
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
(a) SO2 +H2O H2SO3
(b) P2O5 +3H2O 2H3PO4
(c) CO2 + H2O H2CO3
Name an acid used:
(a) To flavor and preserve food
(b) In a drink
(c) To remove ink spots
(d) As an eyewash
(a) Citric acid
(b) Carbonic acid
(c) Oxalic acid
(d) Boric acid
Give the reaction of acids with
State the conditions under which they react.
(a) Chlorides react with concentrated sulphuric acid on warming to liberate hydrogen chloride.
(b) Nitrates when heated with conc. sulphuric acidproduce more volatile nitric acid.
Both chlorides and nitrates do not react with dilute acids; they react with concentrated acids.
Chapter 3 - Acids, Bases and Salts Exercise Misc.
Write the balanced equations for the preparation of the following compounds (as major product) starting from iron and using only one other substance:
(a) Iron (II) chloride
(b) Iron (III) chloride
(c) Iron (II) sulphate
(d) Iron (II) sulphide
(a) Fe + 2HCl (dil) FeCl2 + H2
(bi) 2Fe (heated) + 3Cl2 (dry) 2FeCl3
(c) Fe + H2SO4 (dil) FeSO4 + H2
(d) Fe + S FeS
Write a balanced reaction for the following conversions (A, B, C, D)
A = HCl
B = Na2CO3
C = HNO3
D = NaOH
A: Fe + 2HCl → FeCl2 + H2
B: FeCl2 + Zn→ ZnCl2 + Fe
Fe + H2CO3 → FeCO3 + H2↑
C: FeCO3 + 2HNO3 → Fe (NO3)2 + H2O + CO2
D: Fe(NO3)2 + 2NaOH → Fe(OH)2 + 2NaNO3
The preparation of Lead sulphate from Lead carbonate is a two-step process. (Lead sulphate cannot be prepared by adding dilute Sulphuric acid to Lead carbonate.)
(a) What is the first step that is required to prepare Lead sulphate from Lead carbonate?
(b) Write the equation for the reaction that will take place when this first step is carried out.
(c) Why is the direct addition of dilute sulphuric acid to Lead carbonate an impractical method of preparing Lead sulphate?
(a) The first step is to convert insoluble lead carbonate into soluble lead nitrate by treating lead carbonate with dilute nitric acid.
(b) PbCO3 (s) + 2HNO3(dil) Pb(NO3)2 (aq) + H2O (l) + CO2
(c) When dilute sulphuric acid is added directly to lead carbonate, the lead sulphate thus formed will be deposited on solid lead carbonate disconnecting lead carbonate from sulphuric acid.
(a) What are the terms defined by the following?
(i) A salt containing a metal ion surrounded by other ions or molecules.
(ii) A base which is soluble in water.
(b) Making use only of substances chosen from those given below:
Dilute sulphuric acidSodium Carbonate
Give equations for the reactions by which you could obtain :
(ii) Sulphur dioxide
(iii) Carbon dioxide
(iv) Zinc carbonate (two steps required)
(i) Complex salts
a. The acid which contains four hydrogen atoms
iv. Acetic acid
b. A black-coloured solid which on reaction with dilute sulphuric acid forms a blue-coloured solution is
ii. Manganese [IV] oxide
iii. Lead [II] oxide
iv. Copper [II] oxide
c. Solution A is a strong acid, B is a weak acid and C is a strong alkali.
i. Which solution contains solute molecules in addition to water molecules?
ii. Which solution will give a gelatinous white precipitate with zinc sulphate solution?
The precipitate disappears when an excess of the solution is added.
iii. Give an example of a weak alkali.
d. Write the equations[s] for the reaction[s] to prepare lead sulphate from lead carbonate.
e. Define the following term - Neutralisation.
f. The diagram given below is to prepare iron [III] chloride in the laboratory:
i. What is substance B?
ii. What is the purpose of B?
iii. Why is iron [III] chloride to be stored in a closed container?
iv. Write the equation for the reaction between iron and chlorine.
a. (iv) Acetic acid
b. (iv) Copper (II) oxide
(i) Solution B
(ii) Solution C
(iii) Ammonium hydroxide solution
e. A neutralisation reaction is when an acid and a base react to form water and a salt, and involves the combination of H+ ions and OH- ions to generate water.
i. B is an anhydrous calcium chloride.
ii. B absorbs moisture from the receiver.
iii. Because iron (III) chloride is highly deliquescent and it absorbs moisture from the surrounding air to form a saturated solution.
a. Select the correct answer from A, B, C, D and E:
(i) Nitroso iron [II] sulphate
(ii) Iron [III] chloride
(iii) Chromium sulphate
(iv) Lead chloride
(v) Sodium chloride
A. A deliquescent compound
B. A compound soluble in hot water but insoluble in cold water
C. A compound which in the aqueous solution state is neutral in nature.
b. Select the correct answer from A, B, C and D:
i. A weak organic acid is
A. Formic acid
B. Sulphuric acid
C. Nitric acid
D. Hydrochloric acid
ii. A complex salt is
A. Zinc sulphate
B. Sodium hydrogen sulphate
C. Iron [ammonium sulphate]
D. Tetrammine copper [II] sulphate
c. Give equations for the following conversions A to E:
d. For the preparation of the following salts, give a balanced equation in each case.
i. Copper [II] sulphate from copper [II] oxide
ii. Iron [III] chloride from the metal iron
iii. Potassium sulphate from KOH solution
iv. Lead [II] chloride from lead carbonate [give two equations]
a. A (ii)
b. (i) A
a. Write the balanced chemical equation: Lead nitrate solution is added to sodium chloride solution.
b. State what happens to crystals or washing soda when exposed to air. Name the phenomenon exhibited.
c. Name the method used for the preparation of the following salts from the list given below:
i. Sodium nitrate
ii. Iron (III) chloride
iii. Lead chloride
iv. Zinc sulphate
v. Sodium hydrogen sulphate list:
A. Simple displacement
C. Decomposition by acid
D. Double decomposition
E. Direct synthesis
a. Pb(NO3)2 + 2NaCl → PbCl2 + 2NaNO3
b. When crystals of washing soda are exposed to air, it loses its water of crystallisation and the phenomenon is known as efflorescence.
i. (B) Neutralisation
ii. (E) Direct synthesis
iii. (D) Double decomposition
iv. (A) Simple displacement
v. (C) Decomposition by acid
a. Match the following :
A. Acid salt
A. Ferrous ammonium sulphate
B. Double salt
B. Contains only ions
C. Ammonium hydroxide solution
C. Sodium hydrogen sulphate
D. Dilute hydrochloric acid
D. Contains only molecules
E. Carbon tetrachloride molecules
E. Contains ions and molecules
a. Select the word/s given which are required to correctly complete the blanks - [ammonia, ammonium carbonate, carbon dioxide, hydrogen, hydronium, hydroxide, precipitate, salt, water]
i. A solution M turns blue litmus red, so it must contain (1) …….. ions; another solution turns red litmus blue, and hence, must contain (2) ………. ions.
ii. When solution M and 0 are mixed together, the products will be (3) …….. and (4) ………….
iii. If a piece of magnesium was put into a solution M, (5) ………….. gas would be evolved.
b. Give a suitable chemical term for:
i. A salt formed by incomplete neutralisation of an acid by a base.
ii. A definite number of water molecules bound to some salts.
iii. The process in which a substance absorbs moisture from the atmospheric air to become moist, and ultimately dissolves in the absorbed water.
c. Choosing the substances from the list given: dil. sulphuric acid, copper, iron, sodium copper [II] carbonate, sodium carbonate, sodium chloride, zinc nitrate.
Write balanced equations for the reactions which would be used in the laboratory to obtain the following salts:
i. sodium sulphate
ii. zinc carbonate
iii. copper [II] sulphate
iv. iron [II] sulphate
i. Acidic salt
ii. Water of crystallisation
i. Sodium sulphate:
2Na + H2SO4 (dil.) → Na2SO4 + H2↑
ii. Zinc carbonate:
Zn(NO3)2 + CuCO3→ ZnCO3 + Cu(NO3)2
iii. Copper (II) sulphate:
CuCO3 + H2SO4 (dil.) → CuSO4 + H2O + CO2
iv. Iron (II) sulphate:
Fe + H2SO4 (dil.) → FeSO4 + H2↑
a. Fill in the blank from the choices given: The basicity of acetic acid is …………… [3, 1, 4].
b. Draw the structure of the stable positive ion formed when an acid dissolves in water.
c. State the inference drawn from the observation:
Salt S is prepared by reacting dilute sulphuric acid
with copper oxide. Identify S.
d. Give balanced chemical equations for the preparation of the following salts:
i. Lead sulphate - from lead carbonate
ii. Sodium sulphate - using dilute sulphuric acid
iii. Copper chloride - using copper carbonate
b. The stable positive ion formed when an acid dissolves in water is hydronium ion. The structure of hydronium ion (H3O+) is as follows:
c. Salt S is prepared by reacting dilute sulphuric acid with copper oxide. Hence, salt S is copper sulphate.
i. Lead sulphate from lead carbonate
ii. Sodium sulphate using dilute sulphuric acid Dilute sulphuric acid neutralises bases (oxides and hydroxides) to form salts and water.
iii. Copper chloride using copper carbonate
(a) From the list of salts
AgCl, MgCl2,NaHSO4,PbCO3,ZnCO3,KNO3, Ca(NO3)2,
choose the salt that most appropriately fits the description given below:
(i) A deliquescent salt (ii) An insoluble chloride
(b) From Na2O, SO2, SiO2,Al2O3,MgO, CO, select an oxide which dissolves in water forming an acid.
A deliquescent salt
An insoluble chloride
(b) SO2 is an acidic oxide which dissolves in water forming an acid.
Match the salts given in Column I with their method of preparation given in Column II :
(i) Pb(NO3)2 from PbO
(ii) MgCl2 from Mg
(iii) FeCl3 from Fe
(iv) NaNO3 from NaOH
(v) ZnCO3 from ZnSO4
A) Simple displacement
Pb(NO3)2 from PbO
MgCl2 from Mg
FeCl3 from Fe
NaNO3 from NaOH
ZnCO3 from ZnSO4
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