International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

When an acid reacts with a metal, what does it produce?

1. Salt and hydroxide

2. Salt and carbon dioxide

3. Salt and hydrogen

4. Salt and oxygen

The correct answer is: Salt and hydrogen

When an acid reacts with a metal, the primary products are salt and hydrogen gas. This is a classic reaction in chemistry, known as a metal-acid reaction. During this process, the acid donates protons (H⁺ ions) to the metal, which typically displaces hydrogen ions from the acid. The metal then combines with the anion from the acid to form a salt, while hydrogen gas is produced as a by-product of the reaction. For instance, if hydrochloric acid (HCl) reacts with zinc (Zn), zinc chloride (ZnCl₂) is produced as the salt, and hydrogen gas (H₂) is released. This reaction can be summarized as: \[ \text{Metal} + \text{Acid} \rightarrow \text{Salt} + \text{Hydrogen Gas} \] This understanding is fundamental in recognizing the behavior of acids with metals, illustrating the typical reactivity and the types of products formed in such reactions. The other options do not accurately describe the outcome of this specific type of chemical reaction. For example, options including hydroxides or oxygen do not align with the expected products when a metal reacts directly with an acid.