Zn + NaOH \\(\rightarrow\\) ___________

\\(Zn + 2NaOH \rightarrow Na_2ZnO_2 + H_2\\)Zinc react with excess sodium hydroxide to form sodium zincate(\\(Na_2ZnO_2\\)) along with hydrogen gas. Zinc is a transition metal which shows moderate reactivity.Zinc reacts with NaOH to form sodium zincate with the evolution of hydrogen gas

A milkman adds a very small amount of baking soda to fresh milk.(a) Why does he shift the \\(pH\\) of the fresh milk from \\(6\\) to slightly alkaline?(b) Why does this milk take a long time to set as curd?

a) When the milk is made more alkaline by adding a base to it, it is basically done to prevent it for more time to turning to curd. That’s why milkman shifts the \\(pH\\) of fresh milk to slightly alkaline by adding a very small amount of baking soda to it as baking soda is alkaline in nature and it neutralizes the acidic nature of milk.b) As this milk is slightly more alkaline than other, therefore, acid produced to set into curd will be neutralized by baking soda added by milkman. Hence, this milk takes a longer time to set as curd.

Identify compound X based on the reactions given below. Also, write the name and chemical formulae of A, B, and C.

Following reactions take place:\\(\mathrm{2NaOH}+\mathrm{Zn} \rightarrow \mathrm{Na}_{2} \mathrm{ZnO}_{2}+\mathrm{H}_{2}\\)\\(\mathrm{NaOH}+\mathrm{HCl} \rightarrow \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O} \\)\\(\mathrm{NaOH}+\mathrm{CH}_{3} \mathrm{COOH} \rightarrow \mathrm{CH}_{3} \mathrm{COONa}+\mathrm{H}_{2} \mathrm{O}\\)X is sodium hydroxide, A is sodium zincate, B is sodium chloride and C is sodium acetate.

Discuss the various reactions that occur in the Solvay process.

In Solvay process, also known as ammonia soda process, carbon dioxide is passed through a brine solution (containing about 28 % NaCl) which is saturated with ammonia to form sodium carbonate. \\(\displaystyle 2NH_3+H_2O+CO_2 \rightarrow (NH_4)_2CO_3 \\)\\(\displaystyle (NH_4)_2CO_3 + H_2O + CO_2 \rightarrow 2NH_4HCO_3\\)\\(\displaystyle NH_4HCO_3 + NaCl \rightarrow NaHCO_3 \downarrow + NH_4Cl \\)The precipitate of sodium bicarbonate is filtered, dried and ignited to form sodium carbonate.\\(\displaystyle 2NaHCO_3 \xrightarrow {heat} Na_2CO_3 + CO_2 + H_2O \\)The carbon dioxide required for the reaction can be obtained by heating limestone (calcium carbonate) to 1300 K in a lime klin. Lime dissolves in water to form calcium hydroxide which is then transferred to the ammonia recovery tower.\\(\displaystyle CaCO_3 \xrightarrow {heat} CaO + CO_2 \\)\\(\displaystyle CaO + H_2O \rightarrow Ca(OH)_2 \\)Ammonia required for the process can be prepared by heating ammonium chloride with calcium hydroxide. \\(\displaystyle 2NH_4Cl + Ca(OH)_2 2 NH_3+CaCl_2+H_2O\\)Hence, the only byproduct of the reaction is calcium chloride.

The products obtained when chlorine gas reacts with cold and dilute aqueous \\(NaOH\\) are:

Case -1: Hot Concentrated NaOHThe reaction between chlorine and hot concentrated sodium hydroxide solution is:\\(NaOH + Cl_2 \rightarrow 5NaCl + NaClO_3 + 3H_2O\\)Case -2:Cold NaOHThe reaction between chlorine and cold dilute sodium hydroxide solution is:\\(2NaOH + Cl_2 \rightarrow NaCl + NaClO + H_2O\\)

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\\).

Baking power which is a salt is used as bakery products which give sodium carbonate and carbon dioxide gas on heating. Sodium carbonate is used to remove the hardness of water. Carbon dioxide turns lime water milky.\\( NaHCO_3 \\) (Sodium bicarbonate) \\( \rightarrow \\) \\(Na_2CO_3\\) (Sodium carbonate) + \\(CO_2\\) (carbon dioxide) + \\( H_2O\\) Therefore,Salt \\(A\\), which is sodium bicarbonate and used as baking powder.Salt \\(B\\) is sodium carbonate, which is used to remove the hardness of water.\\(C\\) is carbon dioxide gas which turns lime water milky.

Which of the following salts does not contain water of crystallisation ?

Blue vitriol is copper sulphate pentahydrate \\({ CuSO }_{ 4 }\cdot 5{ H }_{ 2 }O\\). It has 5 moles of water.Washing soda is sodium carbonate monohydrate \\({ Na }_{ 2 }{ CO }_{ 3 }\cdot { H }_{ 2 }O\\)Gypsum is calcium sulphate dihydrate\\({ CaSO }_{ 4 }\cdot 2{ H }_{ 2 }O\\). It can be used as a fertilizer,a main constituent in many forms of plaster and in blackboard chalk.Baking soda is sodium bicarbonate in anhydrous form without any water of crystallisation and it is widely used as dry fire extinguisher because of its alkali nature.

Give two important uses of washing soda and baking soda.

(a) Two important uses of washing soda:(i) It is used in the manufacture of soap and glass.(ii) It is used to remove the permanent hardness of water.(b) Two important uses of baking soda:(i) It is used for making baking powder.(ii) It is used in soda-fire extinguishers.

How chlorine react with Cold and dilute NaoH?

Chlorine reacts with cold and dilute \\(NaOH\\) to produce a mixture of sodium chloride \\((NaCl)\\) and sodium hypochloride \\((NaOCl)\\)\\(2NaOH+Cl_2\longrightarrow NaCl+NaOCl+H_2O\\)

When washing soda is heated :

when washing soda was strongly heated, it loses all water of crystallization and become anhydrous sodium carbonate. The following reaction took place: \\( { Na }_{ 2 }C{ O }_{ 3 }.10{ H }_{ 2 }O\quad \xrightarrow [ \Delta ]{ -{ 9H }_{ 2 }O } \quad { Na }_{ 2 }C{ O }_{ 3 }.{ H }_{ 2 }O\quad \xrightarrow [ \Delta ]{ -{ H }_{ 2 }O } \quad { Na }_{ 2 }C{ O }_{ 3 } \\)Thus when washing soda is heated it loses water vapour.

Sodium Hydroxide - Preparation, Properties and Uses

definition

Properties of sodium hydroxide

1. It is stable towards heat.
2. It is highly soluble in water and a considerable amount of heat is evolved due to the formation of a number of hydrates, e.g.,

N a O H . H_{2} O

N a O H . 2 H_{2} O

. It is also soluble in alcohol.
3. Aqueous solution of sodium hydroxide is strongly alkaline due to its complete dissociation into

N a^{+}

and

O H^{-}

definition

Uses of sodium hydroxide

1. In the refining of petroleum and vegetable oils.
2. In the purification of bauxite for the extraction of aluminium.
3. As a cleansing agent and in washing powder for machines, metal sheets etc.

definition

Method of prepration of sodium hydroxide

It is generally prepared by electrolysis of sodium chloride in Castner-kellner cell. A brine solution is electrolyzed using mercury cathode and carbon anode. Sodium metal, discharged at the cathode, combine with mercury to form sodium amalgam. Cl gas is evolved at the cathode. The amalgam is treated with water to give sodium hydroxide and hydrogen gas.
Reactions:

2 N a / H g + 2 H_{2} O \to 2 N a O H + H_{2} + H g

Sodium Hydroxide - Preparation, Properties and Uses

definition

Properties of sodium hydroxide

definition

Uses of sodium hydroxide

definition

Method of prepration of sodium hydroxide

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Washing Soda - Preparation, Properties and Uses

Sodium Chloride - Source, Properties and Uses

Baking Soda - Preparation, Properties and Uses

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