Identify the acid in the following reaction. Give a reason.

Here are the answers to the questions:

5. Identify the acid in the following reaction. Give a reason.
$\text{NH}_4^+ \text{(aq)} + \text{OH}^- \text{(aq)} \longrightarrow \text{NH}_3 \text{(aq)} + \text{H}_2\text{O (l)}$

• Acid: $\boxed{\text{NH}_4^+}$
• Reason: In this Brønsted-Lowry acid-base reaction, $\text{NH}_4^+$ acts as an acid because it donates a proton ($\text{H}^+$) to the hydroxide ion ($\text{OH}^-$) to form ammonia ($\text{NH}_3$) and water ($\text{H}_2\text{O}$).

6. State two methods that can be used to remove water hardness.

• Method 1: Boiling (removes temporary hardness by precipitating calcium and magnesium carbonates).
• Method 2: Adding chemicals such as washing soda ($\text{Na}_2\text{CO}_3$) or using ion-exchange resins.

7a) Define the term solubility.
Solubility is the maximum amount of a solute that can dissolve in a given amount of solvent at a specific temperature and pressure to form a saturated solution.