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Page No 90:

Question 1:

Acids
(a) turn blue litmus red
(b) have a sour taste
(c) react with carbonates to give carbon dioxide
(d) all of the above

Answer:

(d) all of the above

Acids have all these three properties.

Page No 90:

Question 2:

Which of the following can be used to neutralise an acid?
(a) common salt
(b) calcium hydroxide
(c) vinegar
(d) water

Answer:

(b) calcium hydroxide

Because calcium hydroxide is a base. A base is used to neutralise an acid.

Page No 90:

Question 3:

When a substance X was added to turmeric, there was no colour change. What can you conclude from this?
(a) X is not a base.
(b) X is an acid.
(c) X is a salt.
(d) X is a base.

Answer:

(a) X is not a base

Turmeric turns to brick red colour when it reacts with a base, but does not change its colour when an acid or a salt is added to it.

Page No 90:

Question 4:

  In which of the following cases will a gas be given off?
(a) Hydrochloric acid is added to sodium carbonate
(b) Sulphuric acid is added to sodium hydroxide
(c) Sulphuric acid is added to copper oxide
(d) Hydrochloric acid is added to zinc oxide

Answer:

(a) Hydrochloric acid is added to sodium carbonate

In this reaction, the products are sodium chloride and water and carbon dioxide gas is evolved.



Page No 91:

Question 5:

  Which of the following is not a salt?
(a) calcium carbonate
(b) sodium hydroxide
(c) potassium nitrate
(d) zinc chloride

Answer:

(b) sodium hydroxide

Because it is a base, not a salt.

Page No 91:

Question 6:

Which property is not common to all inorganic acids?
(a) sour taste
(b) reacts with sodium bicarbonate to give carbon dioxide
(c) forms acid salts
(d) turns blue litmus red

Answer:

(c) forms acid salts

Carbonic acid is a weak inorganic acid and does not react with weak bases and thus does not form acid salts on reaction with them.

Page No 91:

Question 7:

Which of these oxides reacts with water to form sulphuric acid?
(a) SO2
(b) SO3
(c) CO
(d) CO2

Answer:

(b) SO3

Sulphur trioxide (SO3) reacts with water to form sulphuric acid.
      
    SO3 (g)        +        H2O (l)                  H2SO4 (aq)
Sulphur trioxide        Water                   Sulphuric acid

Page No 91:

Question 8:

The table below shows the pH values of some chemicals.

Chemical                           pH
hydrochloric acid                 2
ammonium hydroxide         10
sulphuric acid                       1
acetic acid                             5

Which of the above is the strongest acid?
(a) ammonium hydroxide
(b) acetic acid
(c) hydrochloric acid
(d) sulphuric acid

Answer:

(d) sulphuric acid

Lower the pH value, stronger is the acid.

Page No 91:

Question 9:

 Which among the following is a displacement reaction?
(a) H2SO4 + Mg ⟶ H2 + MgSO4
(b) CaCO3 ⟶ CaO + CO2
(c) 2H2 + O2 ⟶ 2H2O
(d) CuSO4.5H2O ⟶ CuSO4 + 5H2O

Answer:

(a) H2SO4 + Mg ⟶ H2 + MgSO4

In this reaction, magnesium displaces hydrogen from sulphuric acid to form magnesium sulphate.

Page No 91:

Question 10:

Three colourless liquids, P, Q and R are tested with red and blue litmus with the following results.

  P Q R
add red litmus stays red stay red turns blue
add blue litmus turns red stays blue stays blue

Study the results shown in the table above. Which of the following is correct for all three liquids?
P Q R
a. acid neither an acid nor a base alkali
b. alkali neither an acid nor a base acid
c. acid acid alkali
d. acid alkali alkali

Answer:

P Q R
a. acid neither an acid nor a base alkali

An acid turns blue litmus to red but does not change the colour of red litmus. A base turns red litmus to blue but does not change the colour of blue litmus. A substance with no colour change (either blue litmus or red litmus) is neither an acid nor a base.

Page No 91:

Question 11:

Match the compounds in column I with the correct formula in column II.

Column I Column II
a. hydrochloric acid i. NaOH
b. slaked lime ii. H2SO4
c. sulphuric acid iii. H2SO3
d. nitric acid iv. Ca(OH)2
e. sodium hydroxide v. H2CO3
f. calcium carbonate vi. HCl
g. baking soda vii. HNO3
h. sulphurous acid viii. CaCO3
i. carbonic acid ix. NaHCO3

Answer:

Column I Column II
a. hydrochloric acid vi. HCl
b. slaked lime iv. Ca(OH)2
c. sulphuric acid ii. H2SO4
d. nitric acid vii. HNO3
e. sodium hydroxide i. NaOH
f. calcium carbonate viii. CaCO3
g. baking soda ix. NaHCO3
h. sulphurous acid iii. H2SO3
i. carbonic acid v. H2CO3

Page No 91:

Question 12:

State whether the following properties are those of acids, alkalies or both.
(a) sour taste
(b) pH value greater than 7
(c) changes the colour of litmus
(d) soapy to touch
(e) remains colourless in phenolphthalein
(f) may be strong or weak
(g) neutralises bases
(h) dangerous to handle
(i) usually react with metals
(j) turns red in the presence of turmeric

Answer:

(a) sour taste acids
(b) pH value greater than 7 bases
(c) changes the colour of litmus acids and bases
(d) soapy to touch bases
(e) remains colourless in phenolphthalein acids
(f) may be strong or weak acids and bases
(g) neutralises bases acids
(h) dangerous to handle acids and bases
(i) usually reacts with metals acids and bases
(j) turns red in the presence of turmeric bases



Page No 92:

Question 13:

Give five properties of acids with examples and equations showing the chemical reactions involved.

Answer:

Properties of acids are as follows:

1.  Acids react with metals to form metal salts with evolution of hydrogen gas.
    For example, zinc metal reacts with hydrochloric acid to form zinc chloride and hydrogen gas.

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

2.  Acids neutralise bases to form a salt and water.
     For example, hydrochloric acid reacts with sodium hydroxide (base) to form sodium chloride (salt) and  water.

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

3.  Acids react with metal carbonates (metal hydrogen carbonates) to form carbon dioxide gas, metal salt and water.
     For example, sodium carbonate reacts with hydrochloric acid to form sodium chloride, carbon dioxide and water.

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


4.  Acids react with metal oxides to form metal salts and water.
     For example, calcium oxide reacts with hydrochloric acid to form calcium chloride and water.
     
     CaO(s) + 2HCl (aq) CaCl2(aq)+ H2O (l)
    
5.  Acids produce hydrogen ions when dissolved in water.
     For example, nitric acid dissolves in water to produce hydrogen ions and nitrate ions.

          HNO3(aq)    water H+(aq) + N O3-
    

Page No 92:

Question 14:

Give equations to show how you can prepare zinc chloride starting from the following reactants.
(a) zinc
(b) zinc oxide
(c) zinc carbonate

Answer:

(a) Zinc metal reacts with hydrochloric acid to prepare zinc chloride.

   Zn(s) + 2HCl (aq)  ZnCl2 (aq) H2(g)
  
(b) Zinc oxide reacts with hydrochloric acid to prepare zinc chloride.

   ZnO(s) + 2HCl (aq)  ZnCl2(aq) + H2O (g)
  
(c) Zinc carbonate reacts with hydrochloric acid to prepare zinc chloride.

    ZnCO3(s) + 2HCl (aq)  ZnCl2(aq)  + H2O (g)+ CO2(g)

Page No 92:

Question 15:

A colourless liquid turns blue litmus paper red and reacts with magnesium to produce a gas. What type of substance must the colourless liquid be?

Answer:

The colourless liquid must be an acid because it turns blue litmus paper red and reacts with magnesium (metal) to produce hydrogen gas, which is the property of an acid.

Page No 92:

Question 16:

Factory waste often contains acid. If it reaches a river, the acid will kill fish and other river life. This is prevented by adding slaked lime to the waste. How do you think slaked lime helps?

Answer:

The acids in factory waste can cause severe environmental damage by altering the pH level of a water body. Thus, calcium hydroxide [Ca(OH)2], which is an alkali, is added to the factory waste. All metal hydroxides are alkaline in nature. Being a metal hydroxide, slaked lime or calcium hydroxide has alkaline properties. When a base or an alkali reacts with an acid, it undergoes neutralisation reaction and neutralises the acid to form salt and water. The products formed are neutral in nature, and even if they are discharged in a nearby water body, they cannot harm the water body as much as an acid can.

Page No 92:

Question 17:

Define the term neutralisation. Give three examples (with equations) of neutralisation reactions.

Answer:

Neutralisation is a chemical reaction in which an acid and a base react to form a salt and water.
For example,

1. Hydrochloric acid neutralises sodium hydroxide to form sodium chloride and water.
   
HCl(aq) + NaOH (aq)  NaCl (aq) + H2O (l)

2. Sulphuric acid neutralises sodium hydroxide to form sodium sulphate and water.

H2SO4(aq) +2NaOH (aq)  Na2SO4(aq) + 2H2O

3. Nitric acid neutralises potassium hydroxide to form potassium nitrate and water.

    HNO3(aq) + KOH (aq)  KNO3(aq) + H2O (l)

Page No 92:

Question 18:

Write balanced chemical equations to show how you would obtain.
(a) lead nitrate from lead hydroxide.
(b) potassium chloride from potassium hydroxide
(c) calcium chloride from calcium carbonate.
(d) sulphurous acid from sulphur dioxide.
(e) sodium nitrate from sodium carbonate.

Answer:

(a) Lead hydroxide reacts with nitric acid to form lead nitrate.
 
Pb(OH)2 (aq) + 2HNO3 (aq)  Pb(NO3)2 (aq) + 2H2O (l)


(b) Potassium hydroxide reacts with hydrochloric acid to form potassium chloride.

KOH (aq) + HCl (aq)  KCl (aq) + H2O (l)


(c) Calcium carbonate reacts with hydrochloric acid to form calcium chloride.
       
CaCO3 (aq) + 2HCl (aq) CaCl2 (aq) + H2O (l) + CO2 (g)
                   

(d) Sulphur dioxide reacts with water to form sulphurous acid.

SO2 (g) + H2O (l) H2SO3 (aq)


(e) Sodium carbonate reacts with nitric acid to form sodium nitrate.
     
Na2CO3 (aq) + 2HNO3 (aq)  2NaNO3 (aq)  +  H2O (l) + CO2 (g)

Page No 92:

Question 19:

Five solutions A to E were tested with the universal indicator to find their pH. The results are shown below.
A. pH 1
B. pH 4
C. pH 7
D. pH 9
E. pH 11

(a) Which solution is neutral?
(b) Which is strongly acidic?
(c) Which is strongly basic?
(d) Which is weakly acidic?

Answer:

(a) Solution C has pH of 7, so it is neutral.
(b) Solution A has pH of 1, so it is strongly acidic.
(c) Solution E has pH of 11, so it is strongly basic.
(d) Solution B has pH of 4, so it is weakly acidic.

Page No 92:

Question 20:

Rewrite the following by choosing the correct word from each pair in brackets.
Acids are compounds that contain (hydrogen/sulphur) atoms. Sulphuric acid is one such example. It is a (strong/weak) acid. It can be neutralised by (acids/alkalis) to form salts called (sulphites/sulphates).
Many (metals/non-metals) react with acids to give a gas called (hydrogen/oxygen). Acid also react with (carbonates/hydroxides) to give (hydrogen/carbon dioxide) gas.
Phenolphthalein turns (pink/colourless) in acids, while litmus turns (red/blue).

Answer:

Acids are compounds that contain hydrogen atoms. Sulphuric acid is one such example. It is a strong acid. It can be neutralised by alkalis to form salts called sulphates.
Many metals react with acids to give a gas called hydrogen. Acid also reacts with carbonates to give carbon dioxide gas.
Phenolphthalein turns colourless in acids, while litmus turns red.

Page No 92:

Question 21:

For each of the substances listed below. write the formulae of two chemicals that will react together to form the substance.
(a) magnesium nitrate
(b) zinc chloride
(c) calcium sulphate
(d) lead nitrate
(e) potassium sulphate

Answer:

(a) Magnesium (Mg) and nitric acid (HNO3) are two chemicals that will react together to form magnesium nitrate.

(b) Zinc metal (Zn) and hydrochloric acid (HCl) are two chemicals that will react together to form zinc chloride.

(c) Calcium (Ca) and sulphuric acid (H2SO4) are two chemicals that will react together to form calcium sulphate.

(d) Lead metal (Pb) and nitric acid (HNO3) are two chemicals that will react together to form lead nitrate.

(e) Potassium metal (K) and sulphuric acid (H2SO4) are two chemicals that will react together to form potassium sulphate.

Page No 92:

Question 22:

Name the acid and metal you would use for making:
(a) magnesium sulphate
(b) sodium sulphate

Answer:

(a) I will use sulphuric acid and magnesium metal for making magnesium sulphate.
 
(b) I will use sulphuric acid and sodium metal for making sodium sulphate.



Page No 93:

Question 23:

Indicate if the following statements are true or false.
(a) Oxides of non-metals dissolve in water to form some acids.
(b) Sulphites are salts formed from sulphuric acid.
(c) Phosphoric acid is tribasic.
(d) Nitric acid can only form normal salts.
(e) Hydrochloric acid can form both carbonates and bicarbonate.
(f) Carbonic acid can form both carbonates and bicarbonates.
(g) Water of crystallisation is found in anhydrous salts.
(h) Litmus turns red in the presence of alkalis.
(i) An acid reacts with a carbonate to form a salt, and hydrogen gas is obtained.
(j) Acid taste sweet.
(k) When the metal zinc reacts with hydrochloric acid, a salt called zinc chloride is formed.
(l) when metals react directly with acids, the reaction is called a displacement reaction.
(m) Sulphuric acid has the formula H2SO3.
(n) Carbon dioxide gas is given off as a result of displacement reactions between acids and metals.

Answer:

(a) True
(b) False
      Sulphates are salts formed from sulphuric acid.
(c) True
(d) True
(e) False
      Hydrochloric acid can form only chlorides, not carbonates and bicarbonates.
(f) True
(g) False
      Anhydrous salt is the salt without water of crystallisation. Water of crystallisation is present in hydrated salts.
(h) False
      Litmus turns blue in the presence of alkalis.
(i) False
      An acid reacts with a carbonate to form a salt, water and carbon dioxide gas is obtained.
(j) False
     Acid tastes sour.
(k) True
(l) True
(m) False
      Sulphuric acid has the formula H2SO4.
(n) False
      Carbon dioxide gas is given off as a result of displacement reaction between acids and metal carbonates.

Page No 93:

Question 24:

Give the names of compounds which will undergo the following reactions.
(a) an acid which will react with magnesium oxide to form magnesium chloride
(b) a base which will react with sulphuric acid to form copper sulphate
(c) the product formed when calcium oxide reacts with water
(d) a substance that turns blue in the presence of alkalies
(e) salt formed when nitric acid reacts with sodium hydroxide
(f) the oxide which dissolves in water to form sulphurous acid
(g) a white salt that turns blue in the presence of moisture

Answer:

(a) Hydrogen chloride is an acid that will react with magnesium oxide to form magnesium chloride.
(b) Copper hydroxide is a base that will react with sulphuric acid to form copper sulphate.
(c) Calcium hydroxide is the product formed when calcium oxide reacts with water.
(d) Red litmus is a substance that turns blue in the presence of alkalies.
(e) Sodium nitrate is the salt formed when nitric acid reacts with sodium hydroxide.
(f) Sulphur dioxide (SO2) is the oxide that dissolves in water to form sulphurous acid.
(g) Anhydrous copper sulphate is a white salt that in the presence of moisture turns blue because of the formation of hydrated copper sulphate.

Page No 93:

Question 25:

Explain the following:
(a) Bee stings are treated with ammonium hydroxide.
(b) When clothes stained with turmeric are washed with soap, they turn red.
(c) Acids or sour foods cannot be cooked in brass vessels.
(d) A medicine containing milk of magnesia and phenolphthalein is pinkish in colour.

Answer:

(a) When a bee stings, it injects an acidic liquid in our body. This acidic liquid is treated by neutralising with ammonium hydroxide (base).

(b) Clothes stained with turmeric when washed with soap, which is basic in nature, turns turmeric to red.

(c) Acids or sour foods (contain acids) cannot be cooked in brass vessel because acid reacts with the copper metal in brass to displace hydrogen from acid and forms copper salt. This salt spoils the food and makes it poisonous to consume.

(d) Milk of magnesia (magnesium hydroxide) is a weak base. When it comes in contact with phenolphthalein, it turns its colour to pink. Thus, this medicine, which is used as an antacid (i.e., to neutralise excess hydrochloric acid in stomach) is pinkish in colour.

Page No 93:

Question 26:

A chemist is given three packets labelled A, B and C. He performs some tests using the substance A, B and C. The tests are explained below in word equations. Can you find out what A, B and C might be? Select your answer from the names that follow. You might find that more than one substance could give the same reaction.

hydrochloric acid, zinc, calcium, lead oxide, sulphur, sodium hydroxide, copper sulphate, carbon

(a) Substance A is an element.
A + oxygen ⟶ oxide
oxide + water ⟶ forms solution
solution + litmus ⟶  blue colour
(b) Substance B is an element.
B + oxygen ⟶  oxide
oxide + water ⟶ solution
solution + litmus ⟶  red colour
(c) Substance C is an element
C + water ⟶ does not dissolve
C + hydrochloric acid ⟶ chloride

Answer:

(a) Substance A might be zinc or calcium. Because both these elements are metals and react with oxygen to form oxide. This oxide on reacting with water forms metal hydroxide, which is basic in nature and turn litmus colour to blue.

(b) Substance B might be sulphur or carbon. Because both these elements are non-metals and react with oxygen to form oxide. This oxide on reacting with water forms acid, which turns litmus colour to red.

(c) Substance C might be zinc. Because it is the element that does not dissolve in water and reacts with hydrochloric acid to form zinc chloride.



Page No 94:

Question 27:

Find the odd one out in each of the following groups, giving reasons for your choice:
(a) litmus, phenolphthalein, turmeric, iodine
(b) citric acid, nitric acid, lactic acid, formic acid
(c) HNO3, H2SO3, H2SO4, H2CO3
(d) CO2, SO2, Na2O, SO3
(e) carbonic acid, sulphuric acid, acetic acid, hydrochloric acid
(f) NaOH, Na2CO3, Na2SO4, NaCl

Answer:

(a) Iodine: Litmus, phenolphthalein and turmeric are acid base indicators but iodine is not.

(b) Nitric acid: It is a strong acid, while citric acid, lactic acid and formic acid are weak acids.

(c) HNO3: It is monobasic acid, while H2SO3, H2SO4 and H2CO3 are dibasic.

(d) Na2O: It is a metal oxide that is basic in nature, while CO2, SO2 and SO3 are non-metal oxides that are acidic in nature.

(e) Sulphuric acid. Because it is a strong acid that furnishes two H+ ions but all other acids furnish single H+ ions. Carbonic acid, although, contains two hydrogen ions, but because of its weak nature, it furnishes only one of its hydrogen ion under normal conditions.

(f) NaOH: It is a base, while Na2CO3, Na2SO4 and NaCl are salts.

Page No 94:

Question 28:

Define an exothermic reaction. Give an example of one such reaction.

Answer:

Exothermic reaction is a reaction in which reactants react to evolve heat energy along with the desired products. For example, neutralisation reaction of hydrochloric acid and sodium hydroxide base.

  HCl (aq)  + NaOH (aq)  NaCl (aq) + H2O + Heat      



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