Salts and their Uses Questions in English

(B) The chemical formula $CaOCl_2$ represents Calcium oxychloride.
Its common name is bleaching powder.
It is widely used for disinfecting water and bleaching cotton and linen in the textile industry.

(C) Calcium hydroxide,represented by the chemical formula $Ca(OH)_2$,reacts with chlorine gas $(Cl_2)$ to produce bleaching powder,which is chemically known as calcium oxychloride $(CaOCl_2)$. The chemical equation for this reaction is: $Ca(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O$.

(D) Washing soda,chemically known as sodium carbonate decahydrate $(Na_2CO_3 \cdot 10H_2O)$,is used for softening hard water. It reacts with the calcium and magnesium salts present in hard water to form insoluble precipitates,thereby removing the hardness.

(N/A) When a solution of sodium hydrogencarbonate $(NaHCO_3)$ is heated,it undergoes thermal decomposition to form sodium carbonate $(Na_2CO_3)$,water $(H_2O)$,and carbon dioxide $(CO_2)$ gas.
The chemical equation for this reaction is:
$2NaHCO_3(s) \xrightarrow{\Delta} Na_2CO_3(s) + H_2O(l) + CO_2(g) \uparrow$

(N/A) The chemical equation for the reaction of Plaster of Paris and water is as follows:
$CaSO_4 \cdot \frac{1}{2}H_2O + 1\frac{1}{2}H_2O \rightarrow CaSO_4 \cdot 2H_2O$
In this reaction,Plaster of Paris (calcium sulphate hemihydrate) reacts with water to form Gypsum (calcium sulphate dihydrate),which is a hard solid mass.

(N/A) Plaster of Paris $(POP)$ should be stored in a moisture-proof container because it is a powdery substance that reacts with atmospheric moisture to form a hard,solid mass known as gypsum.
The chemical reaction is as follows:
$CaSO_4 \cdot \frac{1}{2}H_2O + 1\frac{1}{2}H_2O \rightarrow CaSO_4 \cdot 2H_2O$ (Gypsum,a hard solid).

(N/A) Two important uses of washing soda and baking soda are as follows:
$(1)$ Washing soda:
$(a)$ It is used in glass,soap,and paper industries.
$(b)$ It is used to remove permanent hardness of water.
$(2)$ Baking soda:
$(a)$ It is used as baking powder. Baking powder is a mixture of baking soda and a mild acid known as tartaric acid. When it is heated or mixed in water,it releases $CO_{2}$ that makes bread or cake fluffy.
$(b)$ It is used in soda-acid fire extinguishers.

(D) Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt.
$1$. Blue vitriol is $CuSO_4 \cdot 5H_2O$, which contains $5$ molecules of water of crystallisation.
$2$. Gypsum is $CaSO_4 \cdot 2H_2O$, which contains $2$ molecules of water of crystallisation.
$3$. Washing soda is $Na_2CO_3 \cdot 10H_2O$, which contains $10$ molecules of water of crystallisation.
$4$. Baking soda is $NaHCO_3$, which does not contain any water of crystallisation.
Therefore, the correct option is $D$.

(A) Sodium carbonate $(Na_2CO_3)$ is formed by the neutralization reaction between sodium hydroxide $(NaOH)$ and carbonic acid $(H_2CO_3)$.
$NaOH$ is a strong base,while $H_2CO_3$ is a weak acid.
When a strong base reacts with a weak acid,the resulting salt is basic in nature because the strong base dominates the properties of the salt.
Therefore,sodium carbonate is a basic salt.

(B) Tooth enamel is made up of calcium phosphate,which is the hardest substance in the human body.
Calcium phosphate is a salt formed by the reaction of a strong base (calcium hydroxide) and a weak acid (phosphoric acid).
Since it is a salt of a strong base and a weak acid,its chemical nature is basic.

(B) Common salt $(NaCl)$ is a crucial raw material for various chemicals:
$1$. Washing soda $(Na_2CO_3 \cdot 10H_2O)$ is produced from $NaCl$ via the Solvay process.
$2$. Bleaching powder $(CaOCl_2)$ is produced by the action of chlorine on dry slaked lime, where chlorine is obtained from the electrolysis of brine ($NaCl$ solution).
$3$. Baking soda $(NaHCO_3)$ is produced from $NaCl$, $NH_3$, $H_2O$, and $CO_2$.
$4$. Slaked lime $(Ca(OH)_2)$ is produced by adding water to quicklime $(CaO)$, not from common salt.
Therefore, $(i)$, $(ii)$, and $(iii)$ are correct.

(D) Baking powder is a mixture of sodium hydrogencarbonate $(NaHCO_3)$ and a mild edible acid, such as tartaric acid.
When baking powder is heated or mixed with water, the following reaction takes place:
$NaHCO_3 + H^+ \text{ (from acid)} \rightarrow CO_2 + H_2O + \text{Sodium salt of acid}$.
The carbon dioxide produced during this reaction causes bread or cake to rise, making them soft and spongy.
Tartaric acid is used because it is a weak acid that does not make the food taste sour.

(B) The chlor-alkali process is the electrolysis of an aqueous solution of sodium chloride (brine).
In this process,electricity is passed through a concentrated aqueous solution of $NaCl$ (brine).
This results in the decomposition of $NaCl$ to form sodium hydroxide $(NaOH)$,chlorine gas $(Cl_2)$,and hydrogen gas $(H_2)$.
The chemical equation is: $2 NaCl (aq) + 2 H_2O (l) \rightarrow 2 NaOH (aq) + Cl_2 (g) + H_2 (g)$.
Therefore,option $B$ is the correct representation.

(D) The correct matches are as follows:
$(a)$ Plaster of Paris is $CaSO_{4} \cdot 1/2 H_{2}O$ $(ii)$.
$(b)$ Gypsum is $CaSO_{4} \cdot 2H_{2}O$ $(iii)$.
$(c)$ Bleaching Powder is $CaOCl_{2}$ $(iv)$.
$(d)$ Slaked Lime is $Ca(OH)_{2}$ $(i)$.
Therefore, the correct sequence is $(a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)$.

(A) The salt $A$ used in bakery products is baking soda,which is sodium hydrogen carbonate $(NaHCO_3)$.
On heating,it undergoes thermal decomposition as follows:
$2NaHCO_3 \xrightarrow{\Delta} Na_2CO_3 + H_2O + CO_2 \uparrow$
Here,$B$ is sodium carbonate $(Na_2CO_3)$,which is used for the removal of permanent hardness of water.
The gas $C$ evolved is carbon dioxide $(CO_2)$.
When $CO_2$ gas is passed through lime water $[Ca(OH)_2]$,it forms calcium carbonate $(CaCO_3)$,which makes the solution milky:
$Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O$
Thus,$A = NaHCO_3$,$B = Na_2CO_3$,and $C = CO_2$.

(X=CL_2, Y=CAOCL_2) In the chlor-alkali process for the manufacture of sodium hydroxide,hydrogen gas and chlorine gas $(X)$ are formed as by-products.
When chlorine gas $(X)$ reacts with dry slaked lime (lime water),it forms calcium oxychloride (bleaching powder),which is compound $Y$.
The chemical reactions are as follows:
$2NaCl(aq) + 2H_2O(l) \rightarrow 2NaOH(aq) + Cl_2(g) + H_2(g)$
Here,$X = Cl_2$ (Chlorine gas).
$Ca(OH)_2(s) + Cl_2(g) \rightarrow CaOCl_2(s) + H_2O(l)$
Here,$Y = CaOCl_2$ (Calcium oxychloride or bleaching powder).

(N/A) To identify the acid and base from which a salt is formed, we look at the cation (from the base) and the anion (from the acid). The completed table is as follows:

Name of the salt	Formula	Base	Acid
$(i)$ Ammonium chloride	$NH_{4}Cl$	$NH_{4}OH$	$HCl$
$(ii)$ Copper sulphate	$CuSO_{4}$	$Cu(OH)_{2}$	$H_{2}SO_{4}$
$(iii)$ Sodium chloride	$NaCl$	$NaOH$	$HCl$
$(iv)$ Magnesium nitrate	$Mg(NO_{3})_{2}$	$Mg(OH)_{2}$	$HNO_{3}$
$(v)$ Potassium sulphate	$K_{2}SO_{4}$	$KOH$	$H_{2}SO_{4}$
$(vi)$ Calcium nitrate	$Ca(NO_{3})_{2}$	$Ca(OH)_{2}$	$HNO_{3}$

(A-D) Baking soda is sodium hydrogencarbonate $(NaHCO_3)$. On heating,it decomposes to form sodium carbonate $(Na_2CO_3)$,which is bitter in taste.
$2NaHCO_3 \xrightarrow{\text{Heat}} Na_2CO_3 + H_2O + CO_2$
$(b)$ Baking soda can be converted into baking powder by adding an appropriate amount of a mild edible acid,such as tartaric acid,to it.
$(c)$ The role of tartaric acid is to neutralize the sodium carbonate produced during heating. This prevents the cake from tasting bitter.

(A) The substance described is Plaster of Paris. Its chemical name is calcium sulphate hemihydrate $(CaSO_4 \cdot \frac{1}{2} H_2O)$.
It is a soft powder that,when mixed with water,forms a dough that can be moulded into various shapes. When left in the open,it absorbs moisture from the atmosphere and undergoes a rehydration process to form gypsum $(CaSO_4 \cdot 2H_2O)$,which is a hard solid mass.
The chemical reaction is:
$CaSO_4 \cdot \frac{1}{2} H_2O + 1\frac{1}{2} H_2O \rightarrow CaSO_4 \cdot 2H_2O$
(Plaster of Paris) + (Water) $\rightarrow$ (Gypsum)

(N/A) When hydrated copper sulphate $(CuSO_4 \cdot 5H_2O)$ is heated,the five molecules of water of crystallisation are lost,and the blue-coloured crystals turn into a white anhydrous powder.
If we add water back to this white powder,the blue colour reappears due to the re-formation of hydrated copper sulphate.
The chemical equation is:
$CuSO_4 \cdot 5H_2O (s) \xrightarrow{\text{Heat}} CuSO_4 (s) + 5H_2O (g)$
(Blue) $\quad \quad \quad \quad \quad \quad \quad \quad$ (White)

(N/A) When gypsum $(CaSO_4 \cdot 2H_2O)$ is heated at $373 \, K$,it loses three-fourths of its water of crystallization and forms Plaster of Paris $(CaSO_4 \cdot \frac{1}{2}H_2O)$.
The chemical equation for this reaction is:
$CaSO_4 \cdot 2H_2O(s) \xrightarrow{373 \, K} CaSO_4 \cdot \frac{1}{2}H_2O(s) + 1\frac{1}{2}H_2O(g)$

(N/A) When chlorine gas is passed through dry slaked lime,it reacts to form bleaching powder (calcium oxychloride) and water.
The chemical equation is:
$Ca(OH)_2 + Cl_2 \to CaOCl_2 + H_2O$

(N/A) Chloride of lime,commonly known as bleaching powder,has the chemical formula $CaOCl_{2}$ (calcium oxychloride).
In contrast,calcium chloride has the chemical formula $CaCl_{2}$.
Chemically,chloride of lime contains an oxygen atom bonded to calcium and chlorine,whereas calcium chloride is a simple salt of calcium and chlorine.

(N/A) Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt.
For example, hydrated copper sulphate is represented as $CuSO_{4} \cdot 5H_{2}O$.
In this formula, the $5H_{2}O$ signifies that there are five molecules of water present as water of crystallisation for every one formula unit of copper sulphate.

(N/A) Chemical name: Sodium carbonate.
Chemical formula: $Na_{2}CO_{3} \cdot 10H_{2}O$.
Washing soda is chemically known as sodium carbonate decahydrate,which contains $10$ molecules of water of crystallization.

(N/A) $(i)$ Washing soda contains $10$ molecules of water of crystallisation $(Na_2CO_3 \cdot 10H_2O)$. Plaster of Paris contains $1/2$ molecule of water of crystallisation $(CaSO_4 \cdot 1/2H_2O)$.
$(ii)$ These water molecules are known as water of crystallisation.

(N/A) $(i)$ When sodium hydrogen carbonate $(NaHCO_3)$ is heated, it decomposes to form sodium carbonate $(Na_2CO_3)$, water $(H_2O)$, and carbon dioxide $(CO_2)$ gas.
$(ii)$ The balanced chemical equation for the thermal decomposition of sodium hydrogen carbonate is:
$2NaHCO_3(s) \xrightarrow{\Delta} Na_2CO_3(s) + H_2O(l) + CO_2(g)$

(N/A) Bleaching powder is prepared by the action of chlorine gas $(Cl_2)$ on dry slaked lime $[Ca(OH)_2]$.
The chemical reaction is:
$Ca(OH)_2 + Cl_2 \to CaOCl_2 + H_2O$
Bleaching powder smells strongly of chlorine because it reacts with carbon dioxide $(CO_2)$ present in the atmosphere,which leads to the liberation of free chlorine gas.

(N/A) Bleaching powder is prepared by the action of chlorine gas $(Cl_{2})$ on dry slaked lime $[Ca(OH)_{2}]$.
The chemical reaction is as follows:
$Ca(OH)_{2} + Cl_{2} \rightarrow CaOCl_{2} + H_{2}O$
$(i)$ Bleaching powder does not dissolve completely in water because it contains some amount of unreacted lime $[Ca(OH)_{2}]$,which is insoluble in water. Due to the presence of this unreacted lime,the solution appears milky or leaves a residue when dissolved in water.

(N/A) $(i)$ $A$ hydrated salt is a crystalline salt molecule that is loosely attached to a specific number of water molecules,known as water of crystallisation.
$(ii)$ Two examples of white hydrated salts are:
$1$. Washing soda: $Na_{2}CO_{3} \cdot 10H_{2}O$
$2$. Gypsum: $CaSO_{4} \cdot 2H_{2}O$

(N/A) $(i)$ Sodium acetate $(CH_{3}COONa)$ is formed from the reaction between:
Acid: $CH_{3}COOH$ (Acetic acid)
Base: $NaOH$ (Sodium hydroxide)
$(ii)$ Ammonium chloride $(NH_{4}Cl)$ is formed from the reaction between:
Acid: $HCl$ (Hydrochloric acid)
Base: $NH_{4}OH$ (Ammonium hydroxide)

(N/A) $Na_{2}CO_{3} \cdot 10H_{2}O$ is known as Sodium carbonate decahydrate (Washing soda).
$Na_{2}CO_{3}$ is known as Anhydrous sodium carbonate (Soda ash).
The $10H_{2}O$ represents the water of crystallisation.
Significance of $10H_{2}O$: It is a fixed number of water molecules present in one formula unit of a salt. It is responsible for the specific crystalline shape and,in some cases,the colour of the salt.
The term used for these water molecules is 'water of crystallisation'.

(N/A) The substance is Copper sulphate pentahydrate, with the formula $CuSO_{4} \cdot 5H_{2}O$.
When heated, the blue-coloured hydrated copper sulphate crystals lose their water of crystallisation and turn into white anhydrous copper sulphate $(CuSO_{4})$.
This is a reversible physical change. Upon cooling, the anhydrous salt absorbs moisture from the atmosphere or the water vapour present in the test tube to regain its water of crystallisation, thereby returning to its original blue colour.

(A) $X$ is Sodium hydrogen carbonate $(NaHCO_3)$.
$Y$ is Carbon dioxide $(CO_2)$.
$Z$ is Sodium carbonate $(Na_2CO_3)$.
When $NaHCO_3$ is heated, it decomposes to form sodium carbonate, water, and carbon dioxide:
$2NaHCO_3(s) \xrightarrow{\text{Heat}} Na_2CO_3(s) + H_2O(l) + CO_2(g)$
When $CO_2$ is passed through lime water $[Ca(OH)_2]$, it forms calcium carbonate, which makes the solution milky:
$Ca(OH)_2(aq) + CO_2(g) \rightarrow CaCO_3(s) + H_2O(l)$

(N/A) $(i)$ Soda ash: Anhydrous sodium carbonate; $Na_{2}CO_{3}$
$(ii)$ Blue vitriol: Copper$(II)$ sulphate pentahydrate; $CuSO_{4} \cdot 5H_{2}O$
$(iii)$ Baking soda: Sodium hydrogen carbonate; $NaHCO_{3}$

(N/A) $(i)$ The products obtained in the chlor-alkali process are chlorine gas $(Cl_2)$,hydrogen gas $(H_2)$,and sodium hydroxide $(NaOH)$ solution.
$(ii)$ Chlorine gas $(Cl_2)$ is liberated at the anode,and hydrogen gas $(H_2)$ is liberated at the cathode.
$(iii)$ The solution used as raw material in this process is brine,which is an aqueous solution of sodium chloride $(NaCl)$.

(N/A) $(i)$ Sodium carbonate $(Na_{2}CO_{3})$
(ii) Sodium sulphate $(Na_{2}SO_{4})$

(N/A) The chemical formula of hydrated copper sulphate is $CuSO_4 \cdot 5H_2O$ (blue vitriol),and anhydrous copper sulphate is $CuSO_4$ (white).
Activity: Take some copper sulphate crystals in a dry boiling tube and heat them. The blue colour of the crystals disappears,and the substance becomes white due to the loss of water of crystallisation. If we add a few drops of water to this anhydrous copper sulphate,the blue colour is restored.
$(b)$ Plaster of Paris: Calcium sulphate hemihydrate,$CaSO_4 \cdot \frac{1}{2}H_2O$.
Gypsum: Calcium sulphate dihydrate,$CaSO_4 \cdot 2H_2O$.

(N/A) $(i) \text{ } CaOCl_2(s) + CO_2(g) \to CaCO_3(s) + Cl_2(g)$
$(ii) \text{ } CuSO_4 \cdot 5H_2O(s) \xrightarrow{\text{Heat}} CuSO_4(s) + 5H_2O(g)$
$(iii) \text{ } Ca(OH)_2(s) + Cl_2(g) \to CaOCl_2(s) + H_2O(l)$

(A) : Hydrated copper sulphate $(CuSO_4 \cdot 5H_2O)$
$B$: Water of crystallisation $(H_2O)$
$C$: Anhydrous copper sulphate $(CuSO_4)$
$D$: Water $(H_2O)$
$(b)$ The chemical equations are:
$CuSO_4 \cdot 5H_2O (s) \xrightarrow{\text{Heat}} CuSO_4 (s) + 5H_2O (g)$
(Blue) (White)
$CuSO_4 (s) + 5H_2O (l) \rightarrow CuSO_4 \cdot 5H_2O (s)$
(White) (Blue)
$(c)$ Another salt that shows this property is Ferrous sulphate $(FeSO_4 \cdot 7H_2O)$,which is green in colour and turns white upon heating due to the loss of water of crystallisation.

(N/A) Chemical name: Sodium carbonate decahydrate.
Formula: $Na_{2}CO_{3} \cdot 10H_{2}O$
$(b)$ It is obtained via the Solvay process:
$NaCl + H_{2}O + CO_{2} + NH_{3} \rightarrow NH_{4}Cl + NaHCO_{3}$
$2NaHCO_{3} \xrightarrow{\Delta} Na_{2}CO_{3} + CO_{2} \uparrow + H_{2}O$
$Na_{2}CO_{3} + 10H_{2}O \rightarrow Na_{2}CO_{3} \cdot 10H_{2}O$
$(c)$ It is called a basic salt because it is a salt of a strong base $(NaOH)$ and a weak acid $(H_{2}CO_{3})$,which makes its aqueous solution alkaline.
Use: It is used for removing permanent hardness of water.

(N/A) Reactant: $CaSO_4 \cdot 2H_2O$ is known as Gypsum.
Product: $CaSO_4 \cdot \frac{1}{2}H_2O$ is known as Plaster of Paris $(POP)$.
Use: It is widely used by doctors as plaster for supporting fractured bones in the right position or for making toys,materials for decoration,and surfaces for smooth finishing.

(N/A) The nature of a salt depends on the strength of the acid and base from which it is formed. $A$ salt of a strong base and a weak acid is basic,while a salt of a strong acid and a weak base is acidic.

Salt	Acid	Base	Nature
$(i)$ Sodium acetate	Acetic acid $(CH_3COOH)$	Sodium hydroxide $(NaOH)$	Basic
$(ii)$ Ammonium sulphate	Sulphuric acid $(H_2SO_4)$	Ammonium hydroxide $(NH_4OH)$	Acidic

$A$ salt is formed by the neutralization reaction between an acid and a base. The cation of the salt comes from the base,and the anion comes from the acid.

Salt	Acid and Base
$(i)$ $Na_{2}SO_{4}$	Acid: $H_{2}SO_{4}$,Base: $NaOH$
$(ii)$ $NH_{4}Cl$	Acid: $HCl$,Base: $NH_{4}OH$
$(iii)$ $KNO_{3}$	Acid: $HNO_{3}$,Base: $KOH$
$(iv)$ $NaCl$	Acid: $HCl$,Base: $NaOH$

(N/A) Baking soda is basic in nature,so it neutralizes the acidic effect of the formic acid injected by an ant sting.
$(b)$ Baking soda $(NaHCO_{3})$ reacts with tartaric acid present in baking powder upon heating or mixing with water to release $CO_{2}$ gas. This $CO_{2}$ gas gets trapped in the dough,making the bread or cake soft and spongy.
$(c)$ Baking soda reacts with an acid (like $H_{2}SO_{4}$) to produce a large volume of $CO_{2}$ gas,which cuts off the oxygen supply and extinguishes the fire.

(N/A) The chemical formula of bleaching powder is $CaOCl_{2}$.
Bleaching powder is prepared by the action of chlorine gas on dry slaked lime $[Ca(OH)_{2}]$. The chemical equation for the reaction is:
$Ca(OH)_{2} + Cl_{2} \longrightarrow CaOCl_{2} + H_{2}O$
In drinking water,it is used as a disinfectant to kill germs and bacteria,making the water safe for consumption.

(B) The chemical compound used in glass, soap, and paper industries is sodium carbonate, commonly known as washing soda $(Na_2CO_3 \cdot 10H_2O)$.
It is widely used in the glass, soap, and paper industries because it acts as a strong base and a cleaning agent.
Baking soda $(NaHCO_3)$ is primarily used for cooking and as an antacid.
Lime water $(Ca(OH)_2)$ is used in the laboratory and for whitewashing.
Bleaching powder $(CaOCl_2)$ is used for disinfecting water and bleaching fabrics.

(C) Gypsum is a naturally occurring mineral with the chemical formula $CaSO_4 \cdot 2H_2O$ (calcium sulfate dihydrate).
Plaster of Paris is produced by heating gypsum at $373 \ K$ $(100^{\circ}C)$,which causes it to lose water molecules and become calcium sulfate hemihydrate,with the formula $CaSO_4 \cdot \frac{1}{2}H_2O$.

(D) Bleaching powder,chemically known as calcium oxychloride $(CaOCl_2)$,is widely used as an oxidising agent in many chemical industries.
It acts as a strong oxidising agent because it releases nascent oxygen when it reacts with water or dilute acids.
This property makes it useful for bleaching cotton and linen in the textile industry,bleaching wood pulp in paper factories,and for disinfecting drinking water.

(C) Permanent hardness of water is caused by the presence of dissolved chlorides and sulfates of calcium and magnesium.
Sodium carbonate $(Na_{2}CO_{3})$,commonly known as washing soda,is used to remove this permanent hardness.
It reacts with the calcium and magnesium ions to form insoluble carbonates,which can then be filtered out.
The chemical reaction is: $Ca^{2+} + CO_{3}^{2-} \rightarrow CaCO_{3} \downarrow$ and $Mg^{2+} + CO_{3}^{2-} \rightarrow MgCO_{3} \downarrow$.
Therefore,$Na_{2}CO_{3}$ is the correct compound.