Which one of the following sodium compounds is used for softening hard water?
Na 2CO 3
Understanding Water Softening with Sodium Compounds
Hard water contains a high concentration of dissolved mineral ions, primarily calcium (\((Ca^{2+}\\))) and magnesium (\((Mg^{2+}\\))). These ions cause various problems, such as the formation of soap scum, which prevents lathering with soap, and the buildup of scale deposits in pipes and appliances.
Why Water Softening is Necessary
Water softening is the process of removing these hardness-causing ions from water. This makes the water more suitable for domestic and industrial use, improving the effectiveness of soaps and detergents and prolonging the life of plumbing and appliances.
Sodium Carbonate (\((Na_2CO_3\\))) for Softening Hard Water
Sodium carbonate, also known as washing soda, is a commonly used chemical for softening hard water, particularly for temporary hardness (caused by dissolved bicarbonates) and permanent hardness (caused by dissolved chlorides and sulfates).
When sodium carbonate is added to hard water, the carbonate ions (\((CO_3^{2-}\\))) react with the calcium and magnesium ions to form insoluble calcium carbonate (\((CaCO_3\\))) and magnesium carbonate (\((MgCO_3\\))). These insoluble compounds precipitate out of the water as a solid, which can then be removed, effectively reducing the concentration of the hardness-causing ions.
The chemical reactions can be represented as:
\((Na_2CO_3(aq) + Ca^{2+}(aq) \\)rightarrow CaCO_3(s) \(downarrow + 2Na^{+}(aq)\\))
\((Na_2CO_3(aq) + Mg^{2+}(aq) \\)rightarrow MgCO_3(s) \(downarrow + 2Na^{+}(aq)\\))
The sodium ions (\((Na^{+}\\))) that are released do not cause hardness, so the water becomes soft.
Analyzing Other Sodium Compounds
Let's consider why the other sodium compounds listed are not typically used for this purpose:
- Sodium Bicarbonate (\((NaHCO_3\\))): Also known as baking soda, sodium bicarbonate is much less effective at precipitating calcium and magnesium ions as carbonates compared to sodium carbonate. It's not a primary agent for significant water softening.
- Sodium Hydroxide (\((NaOH\\))): Sodium hydroxide (caustic soda) can precipitate magnesium ions as magnesium hydroxide (\((Mg(OH)_2\\))) and at high concentrations, calcium hydroxide (\((Ca(OH)_2\\))) might also precipitate. However, using sodium hydroxide can significantly increase the pH of the water, making it alkaline, which is often undesirable. Sodium carbonate is generally preferred for its effectiveness and milder impact on pH.
- Sodium Sulfate (\((Na_2SO_4\\))): Sodium sulfate, often called Glauber's salt, does not react with calcium or magnesium ions to form insoluble compounds. Calcium sulfate (\((CaSO_4\\))) and magnesium sulfate (\((MgSO_4\\))) are soluble in water, so adding sodium sulfate does not remove the hardness-causing ions from the solution.
Based on their chemical properties and reactions with hardness ions, sodium carbonate (\((Na_2CO_3\\))) is the most suitable compound among the options provided for softening hard water by precipitation.
| Compound | Formula | Suitability for Softening Hard Water |
|---|---|---|
| Sodium Carbonate | \((Na_2CO_3\\)) | Highly suitable. Precipitates Ca²⁺ and Mg²⁺ as insoluble carbonates. |
| Sodium Bicarbonate | \((NaHCO_3\\)) | Less suitable. Less effective at precipitating hardness ions. |
| Sodium Hydroxide | \((NaOH\\)) | Moderately suitable but increases pH significantly. Precipitates Mg²⁺ as hydroxide. |
| Sodium Sulfate | \((Na_2SO_4\\)) | Not suitable. Does not precipitate Ca²⁺ or Mg²⁺. |
Revision Table: Sodium Compounds and Water Softening
Reviewing the key points about sodium compounds used in water treatment:
- Hard water contains excess calcium and magnesium ions.
- Water softening removes these ions.
- Sodium carbonate effectively removes Ca²⁺ and Mg²⁺ by forming insoluble precipitates.
- Other sodium compounds like bicarbonate, hydroxide, and sulfate are less effective or less suitable for general water softening compared to sodium carbonate.
Additional Information on Water Hardness and Softening Methods
Water hardness is classified into temporary and permanent hardness. Temporary hardness is due to dissolved calcium and magnesium bicarbonates, which can often be removed by boiling. Permanent hardness is due to dissolved calcium and magnesium sulfates and chlorides and requires chemical treatment or other methods for removal.
Besides precipitation with chemicals like sodium carbonate, another common method for water softening is the ion exchange process. In this method, hard water passes through a resin that exchanges sodium ions for calcium and magnesium ions. This is a very effective method for removing hardness completely.
Similar Questions
Which one of the following is used in soda-acid fire extinguishers?
Which one of the following gases is released mostly from landfills in urban areas?
- Which one among the following pairs of compound and chemical formula is not correctly matched ?
Consider the following statements :
1. The temporary hardness in water is due to the presence of bicarbonates of calcium.
2. The permanent hardness in water is due to the presence of soluble chlorides and sulphates of calcium and magnesium.
3. The permanent hardness in water is removed by adding \(Na_2CO_3\) to water.
Which of the statements given above are correct ?- Which one among the following statements regarding micelles is not correct ?
After a hot sunny day, people sprinkle water on the roof-top because:
Methyl Isocyanate gas, which was involved in the disaster in Bhopal in December 1984, was used in the Union Carbide factory for the production of:
‘German silver’ is used to make decorative articles, coinage metal, ornaments, etc. The name is given because:
- Why do plastics not degrade easily ?
What is the chemical composition of a soda-acid type fire extinguisher?
Important Questions from Chemistry in Everyday Life
Which of the following is a greenhouse gas?
I. Methane
II. Nitrous oxide
The gas which turns lime water milky is:
Liquefied Petroleum Gas (LPG) is mainly a mixture of:
Among the following, the conducting form of carbon is
Which of the following is NOT a Fossil Fuel?
