Aqueous sodium hydroxide is added to a mixture of an aqueous solution of X with some aluminium alloy. On warming, ammonia gas is evolved. When X is treated with aqueous ammonia, a white precipitate that is soluble in excess aqueous ammonia is obtained. What could be the identity of X?
A Ammonium nitrate
B Aluminium sulfate
C Zinc hydroxide
D Zinc nitrate
Could someone explain how to get the answer, thks!
To determine the identity of X, we need to analyze the reactions that occur when it is mixed with aqueous sodium hydroxide and aqueous ammonia.
1. Aqueous sodium hydroxide is added to the mixture of X and the aluminum alloy:
X + NaOH → NaX + H2O
This reaction indicates that X reacts with sodium hydroxide to form sodium salt (NaX) and water.
2. On warming the mixture, ammonia gas (NH3) is evolved:
NaX + H2O → NH3 ↑ + NaOH
This reaction shows that the evolved ammonia gas is a result of the reaction between sodium salt (NaX) and water.
3. When X is treated with aqueous ammonia, a white precipitate is obtained which is soluble in excess aqueous ammonia.
This indicates that X forms a white precipitate with aqueous ammonia, which dissolves when excess ammonia is added.
Based on these reactions, we can conclude that the identity of X is B. Aluminum sulfate.
To identify the substance X, we need to analyze the given information step by step:
1. Aqueous sodium hydroxide is added to a mixture of an aqueous solution of X with some aluminum alloy.
When sodium hydroxide reacts with aluminum, it forms sodium aluminate, which can be written as:
2NaOH + 2Al -> 2Na[Al(OH)4]
2. On warming, ammonia gas is evolved.
The presence of sodium hydroxide facilitates a reaction with ammonia gas formed. The reaction can be represented as:
NH3 + NaOH -> NaNH2 + H2O
The evolved gas is ammonia.
3. When X is treated with aqueous ammonia, a white precipitate that is soluble in excess aqueous ammonia is obtained.
This information indicates that a complex is formed between substance X and ammonia. Ammonium ions can form soluble complexes with certain metals.
Now, let's analyze the answer choices based on our observations:
A. Ammonium nitrate: Ammonium nitrate is an ionic compound that does not contain a metal. It does not fit the description of X.
B. Aluminum sulfate: Aluminum sulfate is an ionic compound containing aluminum. However, when treated with aqueous ammonia, it does not form a white precipitate that is soluble in excess ammonia. So, it is not the answer.
C. Zinc hydroxide: Zinc hydroxide is a white, insoluble precipitate. It does not match the description given for the precipitate formed with aqueous ammonia. Therefore, it is not the answer.
D. Zinc nitrate: Zinc nitrate is an ionic compound that contains zinc. When treated with aqueous ammonia, it forms a white precipitate of zinc hydroxide, which is insoluble in excess ammonia. This matches the description given for substance X.
Therefore, the identity of X is most likely D. Zinc nitrate.
It's important to note that this analysis is based on the given information, and further confirmatory tests may be required for a conclusive identification.