Which of the following statements is/are correct? 1. All the bases are alkali. 2. All alkalis dissolve in water. 3. Alkalis are soapy to touch, bitter in taste and corrosive in nature. Select the correct answer using the code given below :
2 and 3 only
Understanding Bases and Alkalis
This question tests our understanding of bases and alkalis, which are fundamental concepts in chemistry. Let's analyze each statement provided.
Analyzing Each Statement
We need to determine the correctness of the following statements:
- All the bases are alkali.
- All alkalis dissolve in water.
- Alkalis are soapy to touch, bitter in taste and corrosive in nature.
Let's examine each statement carefully:
Statement 1: All the bases are alkali.
A base is a substance that can neutralize an acid. Bases include metal oxides, metal hydroxides, and ammonia. An alkali is specifically a base that dissolves in water. Therefore, while all alkalis are bases, not all bases are alkalis. Many bases, such as copper hydroxide (\(\text{Cu(OH)}_2\)) or iron hydroxide (\(\text{Fe(OH)}_3\)), do not dissolve in water and are thus not considered alkalis.
Based on this definition, Statement 1 is incorrect.
Statement 2: All alkalis dissolve in water.
As per the definition, an alkali is a base that is soluble in water. The term "alkali" is specifically used for water-soluble bases. Common examples include sodium hydroxide (\(\text{NaOH}\)), potassium hydroxide (\(\text{KOH}\)), calcium hydroxide (\(\text{Ca(OH)}_2\)), and ammonia solution (\(\text{NH}_3\text{(aq)}\)).
Based on this definition, Statement 2 is correct.
Statement 3: Alkalis are soapy to touch, bitter in taste and corrosive in nature.
Alkalis possess several characteristic properties. When touched, dilute solutions of alkalis feel slippery or "soapy" due to the reaction with oils on the skin to form soap. Many alkalis have a bitter taste (though it is dangerous to taste chemicals). Concentrated solutions of strong alkalis are highly corrosive, capable of causing severe burns to skin and damage to materials.
Based on these properties, Statement 3 is correct.
Conclusion
Based on the analysis of each statement:
- Statement 1: Incorrect
- Statement 2: Correct
- Statement 3: Correct
Therefore, the correct statements are 2 and 3.
| Statement | Correctness | Reason |
|---|---|---|
| 1. All bases are alkali. | Incorrect | Alkalis are bases that dissolve in water; not all bases are soluble. |
| 2. All alkalis dissolve in water. | Correct | This is the definition of an alkali. |
| 3. Alkalis are soapy, bitter, and corrosive. | Correct | These are characteristic properties of alkalis. |
The correct answer is the one indicating that statements 2 and 3 are correct.
Revision Table: Bases vs Alkalis
| Feature | Base | Alkali |
|---|---|---|
| Definition | Substance that neutralizes acid (usually contains \(\text{OH}^-\) or accepts \(\text{H}^+\)) | A base that dissolves in water (releases \(\text{OH}^-\) ions in water) |
| Solubility in Water | May or may not dissolve in water | Always dissolves in water |
| Relationship | Alkali is a specific type of base | All alkalis are bases |
| Examples | \(\text{NaOH}\), \(\text{KOH}\), \(\text{Ca(OH)}_2\), \(\text{Fe(OH)}_3\), \(\text{CuO}\) | \(\text{NaOH}\), \(\text{KOH}\), \(\text{Ca(OH)}_2\), \(\text{NH}_3\text{(aq)}\) |
Additional Information: Properties of Bases and Alkalis
Understanding the properties of bases and alkalis is crucial in chemistry. Here are some additional points:
- Reaction with Acids: Both bases and alkalis react with acids in a neutralization reaction to form salt and water.
- Effect on Indicators: Bases and alkalis turn red litmus paper blue. They also turn phenolphthalein indicator pink.
- Electrical Conductivity: Solutions of soluble bases (alkalis) conduct electricity because they contain mobile ions (\(\text{metal}^+\) and \(\text{OH}^-\)).
- Safety Precautions: It is important to handle strong bases and alkalis with care as they are corrosive and can cause chemical burns. Never taste or touch chemicals in a laboratory setting unless specifically instructed and proper safety measures are taken.
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