Acids, Bases and Salts
Multiple Choice Questions
1. What happens when a solution of an acid is mixed with a solution of a base in a test tube?
(i) The temperature of the solution increases
(ii) The temperature of the solution decreases
(iii) The temperature of the solution remains the same
(iv) Salt formation takes place
(a) (i) only (b)
(i) and (iii)
(c) (ii) and (iii)
(d) (i) and (iv)
Show Answer
Answer
(d) (i) and (iv)
Explanation
When acid is mixed with a solution of base it results in neutralization reaction. Neutralization is an exothermic reaction which result in the formation salt.
2. An aqueous solution turns red litmus solution blue. Excess addition of which of the following solution would reverse the change?
(a) Baking powder
(b) Lime
(c) Ammonium hydroxide solution
(d) Hydrochloric acid
Show Answer
Answer
(d) Hydrochloric acid
Explanation
If the solution turns red litmus to blue color then the solution should be basic in nature. Its effect can be neutralized by adding an acid hence (d) Hydrochloric acid is the answer.
3. During the preparation of hydrogen chloride gas on a humid day, the gas is usually passed through the guard tube containing calcium chloride. The role of calcium chloride taken in the guard tube is to
(a) absorb the evolved gas
(b) moisten the gas
(c) absorb moisture from the gas
(d) absorb Cl-ions from the evolved gas
Show Answer
Answer
(c) absorb moisture from the gas
Explanation
Calcium is a good dehydrating agent. It has property to absorb moisture. Hence it is used as a desiccant to dry gases and Hydrocarbons in the industries.
4. Which of the following salts does not contain water of crystallisation?
(a) Blue vitriol
(b) Baking soda
(c) Washing soda
(d) Gypsum
Show Answer
Answer
(b) Baking soda
Explanation
Baking sodas is white amorphous powder where as other salts given in the question are crystalline in nature.
5. Sodium carbonate is a basic salt because it is a salt of
(a) strong acid and strong base
(b) weak acid and weak base
(c) strong acid and weak base
(d) weak acid and strong base
Show Answer
Answer
(d) weak acid and strong base
Explanation
Salt formed by weak acid and strong base form strong salt. Here Sodium is a strong base and carbonate is a weak acid.
6. Calcium phosphate is present in tooth enamel. Its nature is
(a) basic
(b) acidic
(c) neutral
(d) amphoteric
Show Answer
Answer
(a) basic
Explanation
Phosphate ion present in calcium phosphate is a strong base and it form a strong salt. Hence calcium phosphate is basic in nature.
7. A sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the ${p H}$ paper yellowish-orange. Which of the following would change the colour of this $pH$ paper to greenish-blue?
(a) Lemon juice
(b) Vinegar
(c) Common salt
(d) An antacid
Show Answer
Answer
(d) An antacid
Explanation
Sample solution turn $pH$ paper yellowish-orange which confirms the acidic nature of the sample. In order to make the color to greenish-blue we have to add an antacid.
8. Which of the following gives the correct increasing order of acidic strength
(a) Water $<$ Acetic acid $<$ Hydrochloric acid
(b) Water < Hydrochloric acid< Acetic acid
(c) Acetic acid < Water < Hydrochloric acid
(d) Hydrochloric acid< Water< Acetic acid
Show Answer
Answer
a) Water $<$ Acetic acid $<$ Hydrochloric acid
Explanation
Water is neutral in its pure form, Acetic acid is an organic acid which is weak in nature and Hydrochloric acid is a strong acid.
9. If a few drops of a concentrated acid accidentally spills over the hand of a student, what should be done?
(a) Wash the hand with saline solution
(b) Wash the hand immediately with plenty of water and apply a paste of sodium hydrogencarbonate
(c) After washing with plenty of water apply solution of sodium hydroxide on the hand
(d) Neutralise the acid with a strong alkali
Show Answer
Answer
(b) Wash the hand immediately with plenty of water and apply a paste of sodium hydrogencarbonate
Explanation
Washing affected hand with plenty of water will reduce the concentration of the acid. Remaining traces of the acid can be neutralized by applying a paste of Hydrogen carbonate which is basic in nature. Though $NaOH$ is also a base but it is corrosive in nature hence it is not used to neutralize the acid.
10. Sodium hydrogencarbonate when added to acetic acid evolves a gas. Which of the following statements are true about the gas evolved?
(i) It turns lime water milky
(ii) It extinguishes a burning splinter
(iii) It dissolves in a solution of sodium hydroxide
(iv) It has a pungent odour
(a) (i) and (ii)
(b) (i), (ii) and (iii)
(c) (ii), (iii) and (iv)
(d) (i) and (iv)
Show Answer
Answer
(a) (i) and (ii)
Explanation
Reaction between Sodium hydrogencarbonate and acetic acid lead to evolution of carbon-di-oxide gas. $CO_2$ turns the lime water milky and extinguish a burning splinter.
11. Common salt besides being used in kitchen can also be used as the raw material for making
(i) washing soda
(ii) bleaching powder
(iii) baking soda
(iv) slaked lime
(a) (i) and (ii)
(b) (i), (ii) and (iv)
(c) (i) and (iii)
(d) (i), (iii) and (iv)
Show Answer
Answer
(a) (i) and (ii)
12. One of the constituents of baking powder is sodium hydrogencarbonate, the other constituent is
(a) hydrochloric acid
(b) tartaric acid
(c) acetic acid
(d) sulphuric acid
Show Answer
Answer
(b) tartaric acid
Explanation
A Mild edible acid along with Sodium Hydrogen Carbonate is used to prepare baking powder. Here acetic acid or citric acid can also be used in place of tartaric acid.
13. To protect tooth decay we are advised to brush our teeth regularly. The nature of the tooth paste commonly used is
(a) acidic
(b) neutral
(c) basic
(d) corrosive
Show Answer
Answer
c) Basic
Explanation
Teeth will be acidic in nature because of bacterial activity in mouth. To neutralize the acid toothpaste will be neutral in nature.
14. Which of the following statements is correct about an aqueous solution of an acid and of a base?
(i) Higher the $pH$, stronger the acid
(ii) Higher the $pH$, weaker the acid
(iii) Lower the $pH$, stronger the base
(iv) Lower the $pH$, weaker the base
(a) (i) and (iii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)
Show Answer
Answer
(d) (ii) and (iv)
Explanation
On a $P{H}$ scale acids are those whose $P{H}$ is below 7 lower is the $PH$ stronger will be acid and similarly Bases are those whose $P{H}$ is more than 7. Higher is the $P{H}$ strong will be acid.
15. The $pH$ of the gastric juices released during digestion is
(a) less than 7
(b) more than 7
(c) equal to 7
(d) equal to 0
Show Answer
Answer
(a) less than 7
Explanation
The PH is acidic to below 7 to ensure easy breakdown of food particles. PH of stomach juices is usually 3.
16. Which of the following phenomena occur, when a small amount of acid is added to water?
(i) Ionisation
(ii) Neutralisation
(iii) Dilution
(iv) Salt formation
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (ii) and (iv)
Show Answer
Answer
(b) (i) and (iii)
17. Which one of the following can be used as an acid-base indicator by a visually impared student?
(a) Litmus
(b) Turmeric
(c) Vanilla essence
(d) Petunia leaves
Show Answer
Answer
(c) Vanilla essence
Explanation
Vanilla essence can be used as an olfactory indicator hence it can be used as acid base indicator by visually impaired students.
18. Which of the following substance will not give carbon dioxide on treatment with dilute acid?
(a) Marble
(b) Limestone
(c) Baking soda
(d) Lime
Show Answer
Answer
(d) Lime
Explanation
Marble, Limestone and baking soda have carbonates which produces $CO_2$ gas. Lime contains Hydroxide which will not produce $CO_2$.
19. Which of the following is acidic in nature?
(a) Lime juice
(b) Human blood
(c) Lime water
(d) Antacid
Show Answer
Answer
(a) Lime juice
Explanation
Lime juice has citric acid in it. Hence it is acidic in nature.
20. In an attempt to demonstrate electrical conductivity through an electrolyte, the following apparatus (Figure 2.1) was set up. Which among the following statement(s) is(are) correct?
(i) Bulb will not glow because electrolyte is not acidic
(ii) Bulb will glow because $NaOH$ is a strong base and furnishes ions for conduction.
(iii) Bulb will not glow because circuit is incomplete
(iv) Bulb will not glow because it depends upon the type of electrolytic solution
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (ii) only
(d) (iv) only
Show Answer
Answer
(c) (ii) only
21. Which of the following is used for dissolution of gold?
(a) Hydrochloric acid
(b) Sulphuric acid
(c) Nitric acid
(d) Aqua regia
Show Answer
Answer
(d) Aqua regia
Explanation
Gold is a nobel metal which will not react even with strong acids, hence aqua regia which is a mixture of Nitric and Hydro chloric acid in the ratio 1:3 is used for dissolution of gold.
22. Which of the following is not a mineral acid?
(a) Hydrochloric acid
(b) Citric acid
(c) Sulphuric acid
(d) Nitric acid
Show Answer
Answer
(b) Citric acid
Explanation
Citric acid is the organic acid hence it is the answer
23. Which among the following is not a base?
(a) $NaOH$
(b) $KOH$
(c) $NH _4 OH$
(d) $C _2 H _5 OH$
Show Answer
Answer
(d) $C _2 H _5 OH$
Explanation
$C _2 H _5 OH$ is an alcohol not a base
24. Which of the following statements is not correct?
(a) All metal carbonates react with acid to give a salt, water and carbon dioxide
(b) All metal oxides react with water to give salt and acid
(c) Some metals react with acids to give salt and hydrogen
(d) Some non metal oxides react with water to form an acid
Show Answer
Answer
(b) All metal oxides react with water to give salt and acid
Explanation
Metal oxides are basic in nature hence they give alkaline solution when dissolved in water.
25. Match the chemical substances given in Column (A) with their appropriate application given in Column (B)
| Column (A) | Column (B) |
|---|---|
| (A) Bleaching powder | (i) Preparation of glass |
| (B) Baking soda | (ii) Production of $H _2$ and $Cl _2$ |
| (C) Washing soda | (iii) Decolourisation |
| (D) Sodium chloride | (iv) Antacid |
(a) A-(ii), $\quad B-$ (i), $\quad C-$ (iv), $\quad D-$ (iii)
(b) A-(iii), $\quad$ B-(ii), $\quad$ C-(iv), $\quad$ D-(i)
(c) A-(iii), $\quad$ B-(iv), $\quad$ C-(i), $\quad$ D-(ii)
(d) A-(ii), $\quad$ B-(iv), $\quad$ C-(i), $\quad$ D-(iii)
Show Answer
Answer
(c) A-(iii), $\quad$ B-(iv), $\quad$ C-(i), $\quad$ D-(ii)
26. Equal volumes of hydrochloric acid and sodium hydroxide solutions of same concentration are mixed and the $pH$ of the resulting solution is checked with a $pH$ paper. What would be the colour obtained? (You may use colour guide given in Figure 2.2
(a) Red
(b) Yellow
(c) Yellowish green
(d) Blue
Show Answer
Answer
(c) Yellowish green
Explanation
Here neutralization takes place between HCL and NAOH solution hence $P{H}$ will remain neutral which will be in the yellowish green zone in $P{H}$ paper.
27. Which of the following is(are) true when $HCl(g)$ is passed through water?
(i) It does not ionise in the solution as it is a covalent compound.
(ii) It ionises in the solution
(iii) It gives both hydrogen and hydroxyl ion in the solution
(iv) It forms hydronium ion in the solution due to the combination of hydrogen ion with water molecule
(a) (i) only
(b) (iii) only
(c) (ii) and (iv)
(d) (iii) and (iv)
Show Answer
Answer
(c) (ii) and (iv)
Explanation
HCL is a strong acid which ionizes completely in water to produce Hydrogen as well as Hydrogen and chlorine. Hydrogen produces combine with water molecules to give Hydronium ions.
28. Which of the following statements is true for acids?
(a) Bitter and change red litmus to blue
(b) Sour and change red litmus to blue
(c) Sour and change blue litmus to red
(d) Bitter and change blue litmus to red
Show Answer
Answer
(c) Sour and change blue litmus to red
29. Which of the following are present in a dilute aqueous solution of hydrochloric acid?
(a) $H_3O+Cl^{-}$
(b) ${H _3 O}+{O H}^{-}$
(c) $Cl^{-}+OH^{-}$
(d) unionised $HCl$
Show Answer
Answer
(a) $H _3 O+Cl^{-}$
Explanation
Acid produces Hydrogen which will combine with water molecule to produce Hydronium ion.
30. Identify the correct representation of reaction occurring during chloralkali process
(a) $\quad 2 \mathrm{NaCl}(\mathrm{l})+2 \mathrm{H}_2 \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{NaOH}(\mathrm{l})+\mathrm{Cl}_2(\mathrm{~g})+\mathrm{H}_2(\mathrm{~g})$
(b) $2 \mathrm{NaCl}(\mathrm{aq})+2 \mathrm{H}_2 \mathrm{O}(\mathrm{aq}) \rightarrow 2 \mathrm{NaOH}(\mathrm{aq})+\mathrm{Cl}_2(\mathrm{~g})+\mathrm{H}_2(\mathrm{~g})$
(c) $2 \mathrm{NaCl}(\mathrm{aq})+2 \mathrm{H}_2 \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{NaOH}(\mathrm{aq})+\mathrm{Cl}_2(\mathrm{aq})+\mathrm{H}_2(\mathrm{aq})$
(d) $2 \mathrm{NaCl}(\mathrm{aq})+2 \mathrm{H}_2 \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{NaOH}(\mathrm{aq})+\mathrm{Cl}_2(\mathrm{~g})+\mathrm{H}_2(\mathrm{~g})$
Show Answer
Answer
(d) $2 \mathrm{NaCl}(\mathrm{aq})+2 \mathrm{H}_2 \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{NaOH}(\mathrm{aq})+\mathrm{Cl}_2(\mathrm{~g})+\mathrm{H}_2(\mathrm{~g})$
Short Answer Questions
31. Match the acids given in Column (A) with their correct source given in Column (B)
| Column (A) | Column (B) |
|---|---|
| (a) Lactic acid | (i) Tomato |
| (b) Acetic acid | (ii) Lemon |
| (c) Citric acid | (iii) Vinegar |
| (d) Oxalic acid | (iv) Curd |
Show Answer
Answer
| Column (A) | Column (B) |
|---|---|
| (a) Lactic acid | (iv) Curd |
| (b) Acetic acid | (iii) Vinegar |
| (c) Citric acid | (ii) Lemon |
| (d) Oxalic acid | (i) Tomato |
Column (A)
(a) Lactic acid
(b) Acetic acid
(c) Citric acid
(d) Oxalic acid Column (B)
(iv) Curd
(iii) Vinegar
(ii) Lemon
(i) Tomato
32. Match the important chemicals given in Column (A) with the chemical formulae given in Column (B)
| Column (A) | Column (B) |
|---|---|
| (a) Plaster of Paris | (i) $Ca(OH)_2$ |
| (b) Gypsum | (ii) $CaSO_4 \cdot 1 / 2 H_2 O$ |
| (c) Bleaching Powder | (iii) $CaSO_4 .2 H_2 O$ |
| (d) Slaked Lime | (iv) $CaOCl_2$ |
Show Answer
Answer
| Column (A) | Column (B) |
|---|---|
| (a) Plaster of Paris | (ii) $CaSO_4 \cdot 1 / 2 H _2O$ |
| (b) Gypsum | (iii) $CaSO_4 \cdot 2 H_2 O$ |
| (c) Bleaching Powder | (iv) $CaOCl_2$ |
| (d) Slaked Lime | (i) $Ca(OH)_2$ |
33. What will be the action of the following substances on litmus paper? Dry HCl gas, Moistened $NH _3$ gas, Lemon juice, Carbonated soft drink, Curd, Soap solution.
Show Answer
Answer
Dry HCl gas- No effect
Moistened $NH_3$ gas- Turns litmus paper to blue colour
Lemon juice- Turns litmus paper to red colour
Carbonated soft drink- Turns litmus paper to blue colour
Curd- Turns litmus paper to red colour
Soap solution- Turns litmus paper to blue colour
34. 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.
Show Answer
Answer
Ant sting release methanoic acid. Chemical formula of methanoic acid is $HCOOH$. If we rub baking soda on the affected area it can give relief from the discomfort caused by ant sting.
35. What happens when nitric acid is added to egg shell?
Show Answer
Answer
Nitric acid dissolved egg shell which is made up of Calcium carbonate. Calcium carbonate on reacting with nitric acid yield Calcium Nitrate and carbon-di-oxide gas.
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?
Show Answer
Answer
Student can use Phenopthalein indicator to check the nature of the solution.
37. How would you distinguish between baking powder and washing soda by heating?
Show Answer
Answer
When we heat baking powder $CO _2$ is released which can be confirmed by passing evolved gas into lime water which will turn milky. This reaction will not happen when you heat washing soda.
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.
Show Answer
Answer
Salt A is Baking soda (Sodium Hydrogen Carbonate) which will turn to Sodium carbonate( Salt B) on heating. Gas $C$ turn lime water milky hence it must be $CO_2$.
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.
Show Answer
Answer
$X=$ Chlorine ( $Cl_2$)
$Y=$ Bleaching powder $(CaOCl _2)$
$Ca(OH) _2(s)+Cl _2(g) \to CaOCl _2(s)+H _2 O-$ Calcium oxychloride (bleaching powder)
40. Fill in the missing data in the following table
| Name of the salt | Formula | Salt obtained from | ||
|---|---|---|---|---|
| Base | Acid | |||
| (i) | Ammonium chloride | NH4Cl | NH4OH | - |
| (ii) | Copper sulphate | - | - | H2SO4 |
| (iii) | Sodium chloride | NaCl | NaOH | - |
| (iv) | Magnesium nitrate | Mg(NO3)2 | - | HNO3 |
| (v) | Potassium sulphate | K2SO4 | - | |
| (vi) | Calcium nitrate | Ca(NO3)2 | Ca(OH)2 | - |
Show Answer
Answer
| Name of the salt | Formula | Salt obtained from | ||
|---|---|---|---|---|
| Base | Acid | |||
| (i) | Ammonium chloride | NH4Cl | NH4OH | HCL |
| (ii) | Copper sulphate | CuSO2 | Cu(OH) 2 | H2SO4 |
| (iii) | Sodium chloride | NaCl | NaOH | HCl |
| (iv) | Magnesium nitrate | Mg(NO3)2 | Mg(OH)2 | HNO3 |
| (v) | Potassium sulphate | K2SO4 | KOH | H2SO4 |
| (vi) | Calcium nitrate | Ca(NO3)2 | Ca(OH)2 | HNO3 |
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.
Show Answer
Answer
Strong acids are those which gets completely ionized and weak acids are those which gets partially ionized.
Hydrochloric acid- Strong Acid
citric acid- Weak Acid
acetic acid- Weak Acid
nitric acid, - Strong Acid
formic acid- Weak Acid
sulphuric acid- Strong 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.
Show Answer
Answer
When Zinc reacts with Dilute acid solution, following reaction takes place Hydrogen gas is evolved
$Zn+2 HCl \longrightarrow ZnCl _2+H _2$
When Hydrogen gas is brought near Burning flame, pop pops up which is the confirmation for evolution of Hydrogen gas.
Long Answer Questions
43. In the following schematic diagram for the preparation of hydrogen gas as shown in Figure 2.3, what would happen if following changes are made?
(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.
Show Answer
Answer
a) In place of Zinc granules if we use Zinc dust reaction speed increases
b) Instead of dilute sulphuric acid if we use dilute hydrochloric acid ZINC Chloride is formed
$ Zn+2 HCl \longrightarrow ZnCl_2+H_2 $
c) If we use copper in place of Zinc there will be no reaction as copper will not react with dilute acids
d) Sodium Zincate is produced if we use $NaOH$ solution in place of acid
$ Zn+2 NaOH \longrightarrow Na_2 ZnO_2+H_2 $
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?
Show Answer
Answer
a) If we use baking soda instead of baking powder taste of the cake will be bitter. Upon heating baking soda sodium carbonate will be formed which will make the cake taste bitter.
$\underset{\text { (Sodium bicarbonate) }}{2 \mathrm{NaHCO}_3(\mathrm{~s})}+\text { Heat } \rightarrow \underset{\text { (Sodium carbonate) }}{\mathrm{Na}_2 \mathrm{CO}_3(\mathrm{~s})}+\underset{\text { (Carbon dioxide) }}{\mathrm{CO}_2(\mathrm{~g})}+\underset{\text { (Water) }}{\mathrm{H}_2 \mathrm{O}(\mathrm{l})}$
b) Baking soda can be converted into baking powder by adding an edible weak acid like tartaric acid.
c) When tartaric acid is dissolved in water it gives out Hydrogen ions. Hydrogen ions reacts with Sodium Carbonate to produce carbon di=oxide which will make the cake fluffy.
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 $Z$.
Show Answer
Answer
$X$ is Calcium . When calcium carbonate reacts with $HCl$ it gives out $CO_2$ gas.
$CaCO_3+HCl \longrightarrow CaCl_2+CO_2+H_2 O$
When $CO _2$ is passed into lime water it turns milky due to formation of Calcium carbonate.
Hence solution Y is lime water
When chlorine gas is passed on dry lime water it gives bleaching powder which is used for disinfecting water.
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.
Show Answer
Answer
A compound which is a byproduct of chloralkali process is $NaOH$. Hence compound B is $NaOH$.
When $NaOH$ is treated with acidic oxide neutralization process occurs. For Example If $NaOH$ is treated with carbon-di-oxide, it gives Sodium carbonate.
$2 NaOH+CO _2 \longrightarrow Na _2 CO _3+H _2O$
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.
Show Answer
Answer
The sulphate salt should be calcium sulphate which is white and soft substance. Calcium sulphate is popularly known as plaster of paris.
Plaster of paris has half
molecule of water of crystallization. When we leave plaster of paris open for some time, it absorbs moisture to gain number of molecules of crystallization. This newly formed compound is called Gypsum which is hard to make moulds.
48. Identify the compound $X$ on the basis of the reactions given below. Also, write the name and chemical formulae of $A, B$ and $C$.
Show Answer
Answer
Identifying the compound $\mathrm{X}$ :
Reaction 1:
- Zinc metal reacts with Sodium hydroxide to form Sodium zincate along with the evolution of hydrogen gas.
- It is also known as a displacement reaction in which a less reactive element is replaced by a more reactive element to form a new compound.
$$\underset{\text { Sodium Hydroxide }}{2 \mathrm{NaOH}(\mathrm{aq})}+\underset{\text { Zinc }}{\mathrm{Zn}}(\mathrm{s}) \rightarrow \underset{\text { Sodium Zincate }}{\mathrm{Na}_2 \mathrm{ZnO}_2(\mathrm{~s})}+\underset{\text { Dihydrogen }}{\mathrm{H}_2(\mathrm{~g})}$$
- So, the compound $\mathrm{A}$ is Sodium zincate $\left(\mathrm{Na}_2 \mathrm{ZnO}_2\right)$
Reaction 2:
- When an acid reacts with a base, it will lead to the formation of salt and water.
- Such reactions are known as neutralization reactions.
- The neutralization reaction between hydrochloric acid and sodium hydroxide can be represented as: $$ \underset{\text { Sodium Hydroxide }}{\mathrm{NaOH}(\mathrm{aq})}+\underset{\text { Hydrochlori acid }}{\mathrm{HCl}}(\mathrm{aq}) \rightarrow \underset{\text { Sodium Chloride}}{\mathrm{NaCl}(\mathrm{aq})}+\underset{\text { Water }}{\mathrm{H}_2 \mathrm{O}(\mathrm{l})} $$
Sodium Hydroxide Hydrochloric acid Sodium Chloride Water
- The compound $\mathrm{B}$ is Sodium chloride $(\mathrm{NaCl})$
Reaction 3:
- Sodium hydroxide reacts with a weak acetic acid, it will lead to the formation of basic salt sodium acetate and water.
- The balanced chemical reaction can be written as: $$ \underset{\text { Spdium Hydroxide }}{\mathrm{NaOH}(\mathrm{aq})}+\underset{\text { Acetic Acid }}{\mathrm{CH}_3 \mathrm{COOH}(\mathrm{aq})} \rightarrow \underset{\text { Sodium acetate }}{\mathrm{CH}_3 \mathrm{COONa}(\mathrm{aq})}+\underset{\text { Water }}{\mathrm{H}_2 \mathrm{O}(\mathrm{l})} $$
Sodium Hydroxide Acetic acid Sodium acetate Water
- The compound $\mathrm{C}$ is Sodium acetate $\left(\mathrm{CH}_3 \mathrm{COONa}\right)$
- The compound $\mathrm{X}$ is Sodium hydroxide $(\mathrm{NaOH})$
Therefore, compounds $\mathrm{A}, \mathrm{B}$, and $\mathrm{C}$ are Sodium zincate $\left(\mathrm{Na}_2 \mathrm{ZnO}_2\right)$, Sodium chloride $(\mathrm{NaCl}$ ), Sodium acetate $\left(\mathrm{CH}_3 \mathrm{COONa}\right.$ ) and compound $\mathrm{X}$ is Sodium hydroxide $(\mathrm{NaOH})$.
