An aqueous solution of a crystalline salt reacts with dilute HCl to give a yellow...
An aqueous solution of a crystalline salt reacts with dilute HCl to give a yellow precipitate and a gas that turned dichromate paper green. The crystalline salt may be
- A) Na2S2O3?5H2O
- B) Na2CO3?10H2O
- C) Na2S
- D) NaHCO3
Correct Answer: C) Na2S
Explanation
This Chemistry question is asking us to identify a crystalline salt that reacts with dilute HCl to produce a yellow precipitate and a gas that turns dichromate paper green in an aqueous solution. We are given four options to choose from: Na2S2O3.5H2O, Na2CO3.10H2O, Na2S, and NaHCO3.The correct answer is Option C, Na2S. When Na2S reacts with dilute HCl, it produces hydrogen sulfide gas (H2S). The H2S gas turns dichromate paper green, which is a test for reducing agents. The yellow precipitate is likely to be sulfur, which is formed when H2S reacts with oxygen in the air. Therefore, the reaction can be represented as follows: Na2S + 2HCl ? H2S + 2NaCl.
It is important to note that Na2S is a reducing agent, which means that it can donate electrons to other substances. Additionally, dilute HCl is an acid that can donate hydrogen ions (H+) when dissolved in water. When Na2S reacts with dilute HCl, it produces H2S gas, which is a reducing agent that can donate electrons to dichromate ions (Cr2O7^2-) in the dichromate paper, turning it green.
In summary, the correct option for this Chemistry question is Option C, Na2S. When Na2S reacts with dilute HCl, it produces H2S gas, which turns dichromate paper green, and a yellow precipitate of sulfur is formed. Na2S is a reducing agent that can donate electrons to dichromate ions in the dichromate paper.