Q. Zn and HCl

“\( \text{Zn} \) and \( \text{HCl} \)” usually means you want the reaction equation and basic description of what happens when zinc metal reacts with hydrochloric acid.

Step 1: Identify the reactants

You have two reactants:

• Solid zinc metal: \( \text{Zn(s)} \)
• Aqueous hydrochloric acid: \( \text{HCl(aq)} \)

Step 2: Predict the type of reaction

Zinc is a metal that can displace hydrogen from acids. That means this will be a single-displacement (redox) reaction.

Step 3: Write the products

When \( \text{Zn} \) reacts with \( \text{HCl} \):

• Zinc forms zinc(II) ions, typically giving \( \text{ZnCl}_2 \).
• Hydrogen ions reduce to produce hydrogen gas, \( \text{H}_2 \).

Step 4: Write the unbalanced chemical equation

\[ \text{Zn(s)} + \text{HCl(aq)} \rightarrow \text{ZnCl}_2(\text{aq}) + \text{H}_2(\text{g}) \]

Step 5: Balance the equation

Check atoms one element at a time.

Balance chlorine (\( \text{Cl} \))

\( \text{ZnCl}_2 \) contains 2 chlorine atoms, so you need 2 HCl molecules for 2 chlorine atoms.

This gives:

\[ \text{Zn(s)} + 2\text{HCl(aq)} \rightarrow \text{ZnCl}_2(\text{aq}) + \text{H}_2(\text{g}) \]

Check hydrogen (\( \text{H} \))

Left side has \(2\) hydrogen atoms from \(2\text{HCl}\). Right side has \( \text{H}_2 \) which also has \(2\) hydrogen atoms. Good.

Check zinc (\( \text{Zn} \))

Left and right each have \(1\) zinc atom. Good.

Step 6: Provide the final balanced reaction

\[ \text{Zn(s)} + 2\text{HCl(aq)} \rightarrow \text{ZnCl}_2(\text{aq}) + \text{H}_2(\text{g}) \]

Optional observation (if this is a typical lab question)

Hydrogen gas \( \text{H}_2(\text{g}) \) is produced, usually seen as bubbling. Zinc dissolves as \( \text{ZnCl}_2 \) forms in solution.