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2 mL each of conc. HCl, HNO(3) and a mix...

2 mL each of conc. HCl, `HNO_(3)` and a mixture of conc. HCl and conc. `HNO_(3)` in the ratio of3 : 1 were taken in test tubes labelled as A, B and C. A small piece of metal was put in each test tube. No change occurred in test tubes A and B but the metal got dissolved in test tube C. The metal could be 

A

Al

B

Au

C

Cu

D

Pt

Text Solution

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The correct Answer is:
To solve the question, we need to analyze the reactions that occur when different metals are placed in the test tubes containing concentrated hydrochloric acid (HCl), concentrated nitric acid (HNO3), and a mixture of both in a 3:1 ratio. ### Step-by-Step Solution: 1. **Identify the Chemicals in Each Test Tube**: - Test Tube A: Contains 2 mL of concentrated HCl. - Test Tube B: Contains 2 mL of concentrated HNO3. - Test Tube C: Contains a mixture of concentrated HCl and HNO3 in a 3:1 ratio. 2. **Analyze the Behavior of Metals in Each Acid**: - **In Test Tube A (HCl)**: Concentrated HCl does not react with all metals. Metals like gold and platinum are resistant to HCl, so no change occurs if the metal is one of these. - **In Test Tube B (HNO3)**: Concentrated HNO3 can dissolve some metals, but it does not react with all. For example, metals like gold and platinum are also resistant to HNO3, so no change occurs here as well. - **In Test Tube C (Aqua Regia)**: The mixture of concentrated HCl and HNO3 in a 3:1 ratio forms aqua regia, which is known to dissolve noble metals like gold (Au) and platinum (Pt). 3. **Conclusion Based on Observations**: - Since no reaction occurred in Test Tubes A and B, the metal placed in these tubes is likely to be gold or platinum, as these metals do not react with HCl or HNO3. - The metal in Test Tube C dissolved because aqua regia can dissolve metals like gold and platinum. 4. **Final Answer**: - The metal that could be dissolved in Test Tube C is either **Gold (Au)** or **Platinum (Pt)**.
To solve the question, we need to analyze the reactions that occur when different metals are placed in the test tubes containing concentrated hydrochloric acid (HCl), concentrated nitric acid (HNO3), and a mixture of both in a 3:1 ratio. ### Step-by-Step Solution: 1. **Identify the Chemicals in Each Test Tube**: - Test Tube A: Contains 2 mL of concentrated HCl. - Test Tube B: Contains 2 mL of concentrated HNO3. - Test Tube C: Contains a mixture of concentrated HCl and HNO3 in a 3:1 ratio. ...
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