EXEMPLAR PROBLEMS – SCIENCE Class X Acids Bases And Salts solutions
Ans. Lactic Acid: Curd
Acetic Acid: Vinegar
Citric Acid: Lemon
Oxalic Acid: Tomato
Ans.(a)— (ii) (b)— (iii) (c)— (iv) (d)— (i)
Q33.What will be the action of the following substances on litmus paper?
Dry HCl gas, Moistened NH3 gas, Lemon juice, Carbonated soft
drink, Curd, Soap solution
Ans.
Q34.Name the acid present in ant sting and give its chemical formula.
Also give the common method to get relief from the discomfort
caused by the ant sting.
Ans. Ant Sting contains formic acid, its effect can be neutralised by applying calamine solution or any other mild base, as when base reacts with acid, they neutralise the effect of each other
Q35.What happens when nitric acid is added to egg shell?
Ans.Egg shells contain calcium carbonate. When nitric acid is added
to it, carbon dioxide gas is evolved. The reaction can be given as
CaCO3 + 2HNO3 → Ca (NO3)2 + H2O + CO2
36. A student prepared solutions of (i) an acid and (ii) a base in two
separate beakers. She forgot to label the solutions and litmus
paper is not available in the laboratory. Since both the solutions
are colourless, how will she distinguish between the two?
Ans.She can use phenolphthalein or other indicators like china rose petals or turmeric . phenolphthalein will remain colorless in acid but will turn pink in base
37.How would you distinguish between baking powder and washing
soda by heating?
Ans. The chemical formula of baking powder is sodium
hydrogencarbonate (NaHCO3). Whereas, that of washing soda is
sodium carbonate (Na2CO3.10H2O)
Sodium hydrogencarbonate on heating gives CO2 gas which will
turn lime water milky whereas no such gas is obtained from
sodium carbonate.
2NaHCO3 ⎯⎯He⎯a⎯t → Na2CO3 + H2O + CO2
Na2CO3.10H2O ⎯⎯He⎯at⎯→ Na2CO3 + 10H2O
However if washing soda was heated at or 500 c of temperature, it decomposes slowly to produce the metal oxide and carbon dioxide
38. Salt A commonly used in bakery products on heating gets
converted into another salt B which itself is used for removal of
hardness of water and a gas C is evolved. The gas C when passed
through lime water, turns it milky. Identify A, B and C.
Ans.Baking powder (NaHCO3), salt A is commonly used in bakery
products. On heating it forms sodium carbonate (Na2CO3), B and
CO2 gas, C is evolved. When CO2 gas is passed through lime
water it forms calcium carbonate (CaCO3), which is slightly soluble
in water making it milky.
A — NaHCO3
B — Na2CO3
C — CO2 gas
39. In one of the industrial processes used for manufacture of sodium
hydroxide, a gas X is formed as by product. The gas X reacts with
lime water to give a compound Y which is used as a bleaching
agent in chemical industry. Identify X and Y giving the chemical
equation of the reactions involved.
Ans.39. In the manufacture of sodium hydroxide, hydrogen gas and chlorine
gas (X) are formed as by–products. When chlorine gas (X) reacts
with lime water, it forms calcium oxychloride (bleaching powder)
Y. The reactions are
2NaCl (aq) + 2H2O(l) → 2NaOH (aq) + Cl2 (g) + H2(g)
X→ Cl 2 (Chlorine gas)
Ca (OH)2 (s) + Cl2 (g) → CaOCl2 (s) + H2O
Y — Calcium oxychloride (bleaching powder)
41. What are strong and weak acids? In the following list of acids,
separate strong acids from weak acids.
Hydrochloric acid, citric acid, acetic acid, nitric acid, formic acid,
sulphuric acid.
Ans.In aqueous solutions strong acids ionise completely and provide
hydronium ions. On the other hand weak acids are partially
ionised and an aqueous solution of same molar concentration
provides a much smaller concentration of H3O+ ions.
Strong acids — Hydrochloric acid, sulphuric acid,
42. When zinc metal is treated with a dilute solution of a strong acid,
a gas is evolved, which is utilised in the hydrogenation of oil. Name
the gas evolved. Write the chemical equation of the reaction involved
and also write a test to detect the gas formed.
Ans.When zinc reacts with dilute solution of strong acid, it forms salt
and hydrogen gas is evolved.
Zn + 2HCl → ZnCl2 + H2
When a burning splinter is brought near the mouth of the test
tube, the gas burns with a pop sound.
(a) In place of zinc granules, same amount of zinc dust is taken in
the test tube
(b) Instead of dilute sulphuric acid, dilute hydrochloric acid is
taken
(c) In place of zinc, copper turnings are taken
(d) Sodium hydroxide is taken in place of dilute sulphuric acid
and the tube is heated.
Ans.43. Hint— (a) Hydrogen gas will evolve with greater speed
(b) Almost same amount of gas is evloved
(c) Hydrogen gas is not evolved
(d) If sodium hydroxide is taken, hydrogen gas will be evolved
Zn + 2NaOH → Na2ZnO2 + H2
Sodium zincate
44. For making cake, baking powder is taken. If at home your mother
uses baking soda instead of baking powder in cake,
(a) how will it affect the taste of the cake and why?
(b) how can baking soda be converted into baking powder?
(c) what is the role of tartaric acid added to baking soda?
Ans.44. (a) Baking soda is sodium hydrogencarbonate. On heating, it is
converted into sodium carbonate which is bitter to taste
2NaHCO3 ⎯⎯H⎯ea⎯t → Na2CO3 + H2O + CO2
(b) Baking soda can be converted into baking powder by the
addition of appropriate amount of tartaric acid to it.
(c) The role of tartaric acid is to neutralise sodium carbonate
and cake will not taste bitter.
45. A metal carbonate X on reacting with an acid gives a gas which
when passed through a solution Y gives the carbonate back. On
the other hand, a gas G that is obtained at anode during electrolysis
of brine is passed on dry Y, it gives a compound Z, used for
disinfecting drinking water. Identity X, Y, G and Z.
Ans.45. The gas evolved at anode during electrolysis of brine is chlorine (G)
When chlorine gas is passed through dry Ca(OH)2 (Y) produces
bleaching powder (Z) used for disinfecting drinking water.
Ca(OH)2 + Cl2 → CaOCl2 + H2O
Slaked Bleaching
lime powder
Since Y and Z are calcium salts, therefore X is also a calcium salt
and is calcium carbonate.
CaCO3 + 2HCl → CaCl2 + CO2 + H2O
Ca(OH)2 + CO2 → CaCO3 + H2O
46. A dry pellet of a common base B, when kept in open absorbs
moisture and turns sticky. The compound is also a by–product of
chloralkali process. Identify B. What type of reaction occurs when
B is treated with an acidic oxide? Write a balanced chemical
equation for one such solution.
Ans.46. Sodium hydroxide (NaOH) is a commonly used base and is
hygroscopic, that is, it absorbs moisture from the atmosphere
and becomes sticky.
The acidic oxides react with base to give salt and water. The
reaction between NaOH and CO2 can be given as
2 NaOH + CO2 → Na2CO3 + H2O
47. A sulphate salt of Group 2 element of the Periodic Table is a white,
soft substance, which can be moulded into different shapes by
making its dough. When this compound is left in open for some
time, it becomes a solid mass and cannot be used for moulding
purposes. Identify the sulphate salt and why does it show such a
behaviour? Give the reaction involved.
Ans. Lactic Acid: Curd
Acetic Acid: Vinegar
Citric Acid: Lemon
Oxalic Acid: Tomato
Ans.(a)— (ii) (b)— (iii) (c)— (iv) (d)— (i)
Q33.What will be the action of the following substances on litmus paper?
Dry HCl gas, Moistened NH3 gas, Lemon juice, Carbonated soft
drink, Curd, Soap solution
Ans.
Q34.Name the acid present in ant sting and give its chemical formula.
Also give the common method to get relief from the discomfort
caused by the ant sting.
Ans. Ant Sting contains formic acid, its effect can be neutralised by applying calamine solution or any other mild base, as when base reacts with acid, they neutralise the effect of each other
Q35.What happens when nitric acid is added to egg shell?
Ans.Egg shells contain calcium carbonate. When nitric acid is added
to it, carbon dioxide gas is evolved. The reaction can be given as
CaCO3 + 2HNO3 → Ca (NO3)2 + H2O + CO2
36. A student prepared solutions of (i) an acid and (ii) a base in two
separate beakers. She forgot to label the solutions and litmus
paper is not available in the laboratory. Since both the solutions
are colourless, how will she distinguish between the two?
Ans.She can use phenolphthalein or other indicators like china rose petals or turmeric . phenolphthalein will remain colorless in acid but will turn pink in base
37.How would you distinguish between baking powder and washing
soda by heating?
Ans. The chemical formula of baking powder is sodium
hydrogencarbonate (NaHCO3). Whereas, that of washing soda is
sodium carbonate (Na2CO3.10H2O)
Sodium hydrogencarbonate on heating gives CO2 gas which will
turn lime water milky whereas no such gas is obtained from
sodium carbonate.
2NaHCO3 ⎯⎯He⎯a⎯t → Na2CO3 + H2O + CO2
Na2CO3.10H2O ⎯⎯He⎯at⎯→ Na2CO3 + 10H2O
However if washing soda was heated at or 500 c of temperature, it decomposes slowly to produce the metal oxide and carbon dioxide
38. Salt A commonly used in bakery products on heating gets
converted into another salt B which itself is used for removal of
hardness of water and a gas C is evolved. The gas C when passed
through lime water, turns it milky. Identify A, B and C.
Ans.Baking powder (NaHCO3), salt A is commonly used in bakery
products. On heating it forms sodium carbonate (Na2CO3), B and
CO2 gas, C is evolved. When CO2 gas is passed through lime
water it forms calcium carbonate (CaCO3), which is slightly soluble
in water making it milky.
A — NaHCO3
B — Na2CO3
C — CO2 gas
39. In one of the industrial processes used for manufacture of sodium
hydroxide, a gas X is formed as by product. The gas X reacts with
lime water to give a compound Y which is used as a bleaching
agent in chemical industry. Identify X and Y giving the chemical
equation of the reactions involved.
Ans.39. In the manufacture of sodium hydroxide, hydrogen gas and chlorine
gas (X) are formed as by–products. When chlorine gas (X) reacts
with lime water, it forms calcium oxychloride (bleaching powder)
Y. The reactions are
2NaCl (aq) + 2H2O(l) → 2NaOH (aq) + Cl2 (g) + H2(g)
X→ Cl 2 (Chlorine gas)
Ca (OH)2 (s) + Cl2 (g) → CaOCl2 (s) + H2O
Y — Calcium oxychloride (bleaching powder)
41. What are strong and weak acids? In the following list of acids,
separate strong acids from weak acids.
Hydrochloric acid, citric acid, acetic acid, nitric acid, formic acid,
sulphuric acid.
Ans.In aqueous solutions strong acids ionise completely and provide
hydronium ions. On the other hand weak acids are partially
ionised and an aqueous solution of same molar concentration
provides a much smaller concentration of H3O+ ions.
Strong acids — Hydrochloric acid, sulphuric acid,
42. When zinc metal is treated with a dilute solution of a strong acid,
a gas is evolved, which is utilised in the hydrogenation of oil. Name
the gas evolved. Write the chemical equation of the reaction involved
and also write a test to detect the gas formed.
Ans.When zinc reacts with dilute solution of strong acid, it forms salt
and hydrogen gas is evolved.
Zn + 2HCl → ZnCl2 + H2
When a burning splinter is brought near the mouth of the test
tube, the gas burns with a pop sound.
(a) In place of zinc granules, same amount of zinc dust is taken in
the test tube
(b) Instead of dilute sulphuric acid, dilute hydrochloric acid is
taken
(c) In place of zinc, copper turnings are taken
(d) Sodium hydroxide is taken in place of dilute sulphuric acid
and the tube is heated.
Ans.43. Hint— (a) Hydrogen gas will evolve with greater speed
(b) Almost same amount of gas is evloved
(c) Hydrogen gas is not evolved
(d) If sodium hydroxide is taken, hydrogen gas will be evolved
Zn + 2NaOH → Na2ZnO2 + H2
Sodium zincate
44. For making cake, baking powder is taken. If at home your mother
uses baking soda instead of baking powder in cake,
(a) how will it affect the taste of the cake and why?
(b) how can baking soda be converted into baking powder?
(c) what is the role of tartaric acid added to baking soda?
Ans.44. (a) Baking soda is sodium hydrogencarbonate. On heating, it is
converted into sodium carbonate which is bitter to taste
2NaHCO3 ⎯⎯H⎯ea⎯t → Na2CO3 + H2O + CO2
(b) Baking soda can be converted into baking powder by the
addition of appropriate amount of tartaric acid to it.
(c) The role of tartaric acid is to neutralise sodium carbonate
and cake will not taste bitter.
45. A metal carbonate X on reacting with an acid gives a gas which
when passed through a solution Y gives the carbonate back. On
the other hand, a gas G that is obtained at anode during electrolysis
of brine is passed on dry Y, it gives a compound Z, used for
disinfecting drinking water. Identity X, Y, G and Z.
Ans.45. The gas evolved at anode during electrolysis of brine is chlorine (G)
When chlorine gas is passed through dry Ca(OH)2 (Y) produces
bleaching powder (Z) used for disinfecting drinking water.
Ca(OH)2 + Cl2 → CaOCl2 + H2O
Slaked Bleaching
lime powder
Since Y and Z are calcium salts, therefore X is also a calcium salt
and is calcium carbonate.
CaCO3 + 2HCl → CaCl2 + CO2 + H2O
Ca(OH)2 + CO2 → CaCO3 + H2O
46. A dry pellet of a common base B, when kept in open absorbs
moisture and turns sticky. The compound is also a by–product of
chloralkali process. Identify B. What type of reaction occurs when
B is treated with an acidic oxide? Write a balanced chemical
equation for one such solution.
Ans.46. Sodium hydroxide (NaOH) is a commonly used base and is
hygroscopic, that is, it absorbs moisture from the atmosphere
and becomes sticky.
The acidic oxides react with base to give salt and water. The
reaction between NaOH and CO2 can be given as
2 NaOH + CO2 → Na2CO3 + H2O
47. A sulphate salt of Group 2 element of the Periodic Table is a white,
soft substance, which can be moulded into different shapes by
making its dough. When this compound is left in open for some
time, it becomes a solid mass and cannot be used for moulding
purposes. Identify the sulphate salt and why does it show such a
behaviour? Give the reaction involved.
Ans.X— NaOH (Sodium hydroxide)
A— Na2ZnO2 (Sodium zincate)
B— NaCl (Sodium chloride)
C— CH3COONa (Sodium acetate)
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