Sodium Carbonate, Sodium Chloride, Sodium Hydroxide — Revision Notes

⚡ 30-Second Revision

Sodium Chloride ($\text{NaCl}$): — Common salt. Raw material for $\text{NaOH}$, $\text{Na}_2\text{CO}_3$. Purified by $\text{HCl}$ gas (common ion effect).
Sodium Hydroxide ($\text{NaOH}$): — Caustic soda. Strong base, deliquescent. Prepared by Chlor-alkali process (electrolysis of brine).

- Anode: $2\text{Cl}^- \rightarrow \text{Cl}_2 + 2\text{e}^-$ - Cathode: $2\text{H}_2\text{O} + 2\text{e}^- \rightarrow \text{H}_2 + 2\text{OH}^-$ - Overall: $2\text{NaCl} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{Cl}_2 + \text{H}_2$

Sodium Carbonate ($\text{Na}_2\text{CO}_3$): — Washing soda ($\text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}$) / Soda ash ($\text{Na}_2\text{CO}_3$). Efflorescent (decahydrate). Aqueous solution is alkaline (hydrolysis of $\text{CO}_3^{2-}$).

- Prepared by Solvay process: $\text{NaCl}$, $\text{CaCO}_3$, $\text{NH}_3$ are raw materials. - Key step: $\text{NH}_4\text{HCO}_3 + \text{NaCl} \rightarrow \text{NaHCO}_3 \downarrow + \text{NH}_4\text{Cl}$ - Heating: $2\text{NaHCO}_3 \xrightarrow{\text{Heat}} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2$ - Recycling: $\text{NH}_3$ and $\text{CO}_2$ are recycled.

2-Minute Revision

For NEET, quickly recall the three key sodium compounds: Sodium Chloride ($\text{NaCl}$), Sodium Hydroxide ($\text{NaOH}$), and Sodium Carbonate ($\text{Na}_2\text{CO}_3$). $\text{NaCl}$ is common salt, purified by passing $\text{HCl}$ gas through its saturated solution, leveraging the common ion effect.

It's a neutral salt and a crucial raw material. $\text{NaOH}$, or caustic soda, is a strong, deliquescent base. Its industrial production is the Chlor-alkali process, involving the electrolysis of brine, yielding $\text{NaOH}$, $\text{Cl}_2$, and $\text{H}_2$.

Remember the reactions at anode ($2\text{Cl}^- \rightarrow \text{Cl}_2$) and cathode ($2\text{H}_2\text{O} \rightarrow \text{H}_2 + 2\text{OH}^-$). $\text{Na}_2\text{CO}_3$, known as washing soda (decahydrate, efflorescent) or soda ash (anhydrous), is produced by the Solvay process.

This process uses $\text{NaCl}$, $\text{CaCO}_3$, and $\text{NH}_3$ as raw materials. Key steps include the formation and precipitation of $\text{NaHCO}_3$, followed by its heating to get $\text{Na}_2\text{CO}_3$.

Crucially, $\text{NH}_3$ and $\text{CO}_2$ are recycled. The aqueous solution of $\text{Na}_2\text{CO}_3$ is alkaline due to carbonate ion hydrolysis. Focus on these preparation methods, unique properties like deliquescence/efflorescence, and major uses for quick recall.

5-Minute Revision

Let's consolidate the essential information on Sodium Carbonate, Sodium Chloride, and Sodium Hydroxide for NEET.

Sodium Chloride (NaCl): This is common salt. Its primary sources are seawater (solar evaporation) and rock salt (mining). Crude salt is purified by dissolving it in water and passing $\text{HCl}$ gas, which precipitates pure $\text{NaCl}$ due to the common ion effect, leaving more soluble impurities like $\text{CaCl}_2$ and $\text{MgCl}_2$ in solution. It's a neutral salt and a fundamental raw material for other sodium compounds.

Sodium Hydroxide (NaOH): Known as caustic soda, it's a white, translucent, deliquescent solid and a very strong base. It's manufactured by the Chlor-alkali process, which is the electrolysis of aqueous $\text{NaCl}$ (brine).

Anode (oxidation): — $2\text{Cl}^- (\text{aq}) \rightarrow \text{Cl}_2 (\text{g}) + 2\text{e}^-$
Cathode (reduction): — $2\text{H}_2\text{O} (\text{l}) + 2\text{e}^- \rightarrow \text{H}_2 (\text{g}) + 2\text{OH}^- (\text{aq})$
Overall: — $2\text{NaCl} (\text{aq}) + 2\text{H}_2\text{O} (\text{l}) \rightarrow 2\text{NaOH} (\text{aq}) + \text{Cl}_2 (\text{g}) + \text{H}_2 (\text{g})$

All three products ($\text{NaOH}$, $\text{Cl}_2$, $\text{H}_2$) are industrially important. Uses of $\text{NaOH}$ include soap, paper, and textile industries.

**Sodium Carbonate (Na$_2$CO$_3$):** This is washing soda ($\text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}$) or soda ash (anhydrous $\text{Na}_2\text{CO}_3$). Washing soda is efflorescent (loses water of crystallization).

Its aqueous solution is alkaline due to the hydrolysis of the carbonate ion ($\text{CO}_3^{2-} + \text{H}_2\text{O} \rightleftharpoons \text{HCO}_3^- + \text{OH}^-$). It's produced by the Solvay process using $\text{NaCl}$, $\text{CaCO}_3$, and $\text{NH}_3$ as raw materials.

Key steps:

1. Ammoniation of brine: $\text{NaCl} + \text{NH}_3 + \text{H}_2\text{O} \rightarrow \text{Ammoniated Brine}$ 2. Carbonation: $\text{NH}_3 + \text{H}_2\text{O} + \text{CO}_2 \rightarrow \text{NH}_4\text{HCO}_3$; then $\text{NH}_4\text{HCO}_3 + \text{NaCl} \rightarrow \text{NaHCO}_3 \downarrow + \text{NH}_4\text{Cl}$ 3.

Heating $\text{NaHCO}_3$: $2\text{NaHCO}_3 \xrightarrow{\text{Heat}} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2$ 4. Ammonia recovery: $2\text{NH}_4\text{Cl} + \text{Ca(OH)}_2 \rightarrow 2\text{NH}_3 + \text{CaCl}_2 + 2\text{H}_2\text{O}$ Ammonia and $\text{CO}_2$ are recycled.

$\text{CaCl}_2$ is a byproduct. Uses include glass, detergents, and water softening. Focus on the distinct properties and the detailed steps of the industrial processes.

Prelims Revision Notes

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Sodium Chloride (NaCl):

* Common Name: Common salt, table salt. * Sources: Seawater (solar evaporation), rock salt (underground deposits). * Purification: Crude salt dissolved in water, $\text{HCl}$ gas passed through it.

Pure $\text{NaCl}$ precipitates due to common ion effect. Impurities ($\text{CaCl}_2$, $\text{MgCl}_2$) remain in solution. * Properties: White crystalline solid, highly soluble in water, neutral solution.

* Uses: Dietary, preservative, raw material for $\text{NaOH}$, $\text{Na}_2\text{CO}_3$, $\text{Cl}_2$, $\text{H}_2$.

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Sodium Hydroxide (NaOH):

* Common Name: Caustic soda. * Nature: Strong base, highly corrosive, deliquescent (absorbs moisture and dissolves). * Preparation: Chlor-alkali process (electrolysis of aqueous $\text{NaCl}$ solution / brine).

* Anode (oxidation): $2\text{Cl}^- (\text{aq}) \rightarrow \text{Cl}_2 (\text{g}) + 2\text{e}^-$ * Cathode (reduction): $2\text{H}_2\text{O} (\text{l}) + 2\text{e}^- \rightarrow \text{H}_2 (\text{g}) + 2\text{OH}^- (\text{aq})$ * Overall Reaction: $2\text{NaCl} (\text{aq}) + 2\text{H}_2\text{O} (\text{l}) \rightarrow 2\text{NaOH} (\text{aq}) + \text{Cl}_2 (\text{g}) + \text{H}_2 (\text{g})$ * Products: $\text{NaOH}$ (alkali), $\text{Cl}_2$ (chlorine), $\text{H}_2$ (hydrogen).

* Uses: Soap and detergents, paper industry, textile industry (mercerizing cotton), petroleum refining, bauxite purification.

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**Sodium Carbonate (Na$_2$CO$_3$):**

* Common Names: Washing soda ($\text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}$), Soda ash (anhydrous $\text{Na}_2\text{CO}_3$). * Nature: Washing soda is efflorescent (loses water of crystallization).

Aqueous solution is alkaline due to hydrolysis of $\text{CO}_3^{2-}$ ions: $\text{CO}_3^{2-} + \text{H}_2\text{O} \rightleftharpoons \text{HCO}_3^- + \text{OH}^-$. * Preparation: Solvay process (Ammonia-soda process).

* Raw Materials: $\text{NaCl}$ (brine), $\text{CaCO}_3$ (limestone), $\text{NH}_3$ (ammonia). * Key Steps & Reactions: 1. Ammoniation of brine: $\text{NaCl} (\text{aq}) + \text{NH}_3 (\text{g}) + \text{H}_2\text{O} (\text{l}) \rightarrow \text{Ammoniated Brine}$ 2.

Carbonation: $\text{NH}_3 + \text{H}_2\text{O} + \text{CO}_2 \rightarrow \text{NH}_4\text{HCO}_3$. Then $\text{NH}_4\text{HCO}_3 + \text{NaCl} \rightarrow \text{NaHCO}_3 \downarrow + \text{NH}_4\text{Cl}$.

($\text{NaHCO}_3$ precipitates due to low solubility). 3. Heating $\text{NaHCO}_3$: $2\text{NaHCO}_3 (\text{s}) \xrightarrow{\text{Heat}} \text{Na}_2\text{CO}_3 (\text{s}) + \text{H}_2\text{O} (\text{g}) + \text{CO}_2 (\text{g})$.

4. Ammonia Recovery: $\text{CaCO}_3 \xrightarrow{\text{Heat}} \text{CaO} + \text{CO}_2$. $\text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2$. $2\text{NH}_4\text{Cl} + \text{Ca(OH)}_2 \rightarrow 2\text{NH}_3 + \text{CaCl}_2 + 2\text{H}_2\text{O}$.

* Recycling: $\text{NH}_3$ and $\text{CO}_2$ are recycled, making the process efficient. * Byproduct: $\text{CaCl}_2$ (limited commercial value, disposal issue). * Uses: Glass industry, detergents, water softening, paper industry, manufacture of borax and other sodium compounds.

Vyyuha Quick Recall

For Sodium Compounds: Caustic Soda is Deliquescent, Washing Soda Effloresces, Solvay Produces Washing Soda.

Caustic Soda ($\text{NaOH}$) is Deliquescent.
Washing Soda ($\text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}$) Effloresces.
Solvay Process Produces Washing Soda ($\text{Na}_2\text{CO}_3$).

This helps remember the key properties and the main production process for sodium carbonate.