Use phenolphthalein to identify the base.

Add a few drops of phenolphthalein indicator to each of the three unknown solutions ($\text{NaCl}$, $\text{HCl}$, $\text{NaOH}$). The solution that turns pink is the base, $\text{NaOH}$. The other two solutions ($\text{NaCl}$ and $\text{HCl}$) will remain colorless.

To the remaining two colorless solutions, add a small piece of a reactive metal like magnesium or zinc, or a carbonate like sodium carbonate.

• The solution that produces effervescence (gas bubbles) is the acid, $\text{HCl}$. (e.g., $\text{Mg}(\text{s}) + \text{2HCl}(\text{aq}) \to \text{MgCl}_2(\text{aq}) + \text{H}_2(\text{g})$ or $\text{Na}_2\text{CO}_3(\text{s}) + \text{2HCl}(\text{aq}) \to \text{2NaCl}(\text{aq}) + \text{H}_2\text{O}(\text{l}) + \text{CO}_2(\text{g})$)
• The solution that shows no visible reaction is the salt, $\text{NaCl}$.

2. Suggest at least three methods for the preparation of salts.

1. Neutralization reaction: Reaction between an acid and a base. Example: $\text{HCl}(\text{aq}) + \text{NaOH}(\text{aq}) \to \text{NaCl}(\text{aq}) + \text{H}_2\text{O}(\text{l})$
2. Reaction of an acid with a reactive metal: Example: $\text{H}_2\text{SO}_4(\text{aq}) + \text{Zn}(\text{s}) \to \text{ZnSO}_4(\text{aq}) + \text{H}_2(\text{g})$
3. Reaction of an acid with a metal oxide: Example: $\text{2HNO}_3(\text{aq}) + \text{CuO}(\text{s}) \to \text{Cu(NO}_3)_2(\text{aq}) + \text{H}_2\text{O}(\text{l})$
4. Precipitation (double decomposition) reaction: Mixing two soluble salt solutions to form an insoluble salt. Example: $\text{AgNO}_3(\text{aq}) + \text{NaCl}(\text{aq}) \to \text{AgCl}(\text{s}) + \text{NaNO}_3(\text{aq})$

3. Classify the following salts as soluble or insoluble in water:

• a. $\text{NH}_4\text{Cl}$: $\boxed{\text{Soluble}}$ (All ammonium salts and most chlorides are soluble)
• b. $\text{K}_3\text{PO}_4$: $\boxed{\text{Soluble}}$ (All alkali metal salts are soluble)
• c. $\text{FeCO}_3$: $\boxed{\text{Insoluble}}$ (Most carbonates are insoluble, except for alkali metal and ammonium carbonates)
• d. $\text{AgCl}$: $\boxed{\text{Insoluble}}$ (Silver chloride is an exception to the general solubility of chlorides)
• e. $\text{AgNO}_3$: $\boxed{\text{Soluble}}$ (All nitrates are soluble)
• f. $\text{CaCl}_2$: $\boxed{\text{Soluble}}$ (Most chlorides are soluble)
• g. $\text{PbSO}_4$: $\boxed{\text{Insoluble}}$ (Lead(II) sulfate is an exception to the general solubility of sulfates)
• h. $\text{Na}_2\text{S}$: $\boxed{\text{Soluble}}$ (All alkali metal sulfides are soluble)
• i. $\text{CaSO}_4$: $\boxed{\text{Insoluble}}$ (Calcium sulfate is sparingly soluble, generally considered insoluble in qualitative analysis)
• j. $\text{BaCO}_3$: $\boxed{\text{Insoluble}}$ (Most carbonates are insoluble, except for alkali metal and ammonium carbonates)

4. Why do aqueous solutions of soluble salts conduct electricity?
Aqueous solutions of soluble salts conduct electricity because when dissolved in water, the salts dissociate into free-moving positive and negative ions. These ions act as charge carriers, allowing the electric current to flow through the solution.

5. Which carbonates do not decompose on heating?
The carbonates of alkali metals (Group 1 elements like sodium and potassium) generally do not decompose on heating, or they require very high temperatures to do so. For example, $\text{Na}_2\text{CO}_3$ and $\text{K}_2\text