The gas produced when ammonium bisulphide is added to an aqueous solution of aluminium sulfate is (a) \(\mathrm{SO}_{3}\) (b) \(\mathrm{SO}_{2}\) (c) \(\mathrm{S}\) (d) \(\mathrm{H}_{2} \mathrm{~S}\)

To understand chemical reactions, it is crucial to start with the basics of balancing chemical equations. This process ensures the law of conservation of mass is followed, meaning that the same number of atoms of each element is present on both sides of the equation. For a balanced equation, each element must have the same subscript number on the reactant side as on the product side.

Take a simple equation like the combustion of methane: \( \text{CH}_4 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \). Here, carbon (C) and hydrogen (H) atoms are balanced, but oxygen (O) atoms are not. To balance oxygen, we adjust the coefficients, the numbers in front of the formulas, to get \( \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} \), which now balances out with 4 oxygen atoms on each side.

In chemical reactions, identifying reactants and products is a fundamental step. Reactants are the substances that undergo a change during a chemical reaction, while products are the new substances formed as a result of that reaction.

For instance, in the reaction between ammonium bisulphide and aluminium sulfate, the reactants are \( (\text{NH}_4)_2\text{S} \) and \( \text{Al}_2(\text{SO}_4)_3 \), while the products include \( (\text{NH}_4)_2\text{SO}_4 \), \( \text{Al}_2\text{S}_3 \), and hydrogen sulfide gas (\( \text{H}_2\text{S} \)). By correctly identifying these reactants and products, we can better understand the changes that occur and can proceed to balance the chemical equation accordingly.

Gas evolution reactions are a type of chemical reactions where a gas is produced as one of the end products. Recognizing these reactions is often straightforward because you can observe the gas being released, sometimes as bubbles or a change in pressure within a sealed system.

In the reaction between ammonium bisulphide and aluminium sulfate, the gas evolved is hydrogen sulfide (\( \text{H}_2\text{S} \)). This gas has a characteristic 'rotten egg' smell, making it relatively simple to identify in a laboratory setting. However, gas evolution can be more complex, involving reactions that produce less evident gases, or where multiple gases are formed. Understanding the properties of the reactants and anticipating the products allows chemists to predict the evolution of gas, as was determined in our provided step by step solution.