What mass of potassium chlorate `(KClO_3)` on heating gives 1.491 g of potassium chloride (KCl) and 0.772 litres of oxygen at NTP?

Explanation

To solve the problem, we need to determine the mass of potassium chlorate (KClO₃) that decomposes to yield a specific mass of potassium chloride (KCl) and a specific volume of oxygen gas (O₂) at normal temperature and pressure (NTP).

### Step-by-Step Solution:

1. **Write the Decomposition Reaction**:
The decomposition of potassium chlorate can be represented by the following balanced chemical equation:
\[ 2 \text{KClO}_3 \rightarrow 2 \text{KCl} + 3 \text{O}_2 \]

2. **Identify Given Data**:
- Mass of potassium chloride (KCl) produced = 1.491 g
- Volume of oxygen (O₂) produced = 0.772 L at NTP

3. **Calculate Moles of Oxygen Produced**:
At NTP, 1 mole of gas occupies 22.4 L. Therefore, the number of moles of oxygen produced can be calculated as:
\[ \text{Moles of } O_2 = \frac{\text{Volume of } O_2}{22.4 \text{ L}} = \frac{0.772 \text{ L}}{22.4 \text{ L/mol}} \approx 0.0345 \text{ moles} \]

4. **Calculate Mass of Oxygen Produced**:
The molar mass of oxygen (O₂) is 32 g/mol. Therefore, the mass of oxygen produced can be calculated as:
\[ \text{Mass of } O_2 = \text{Moles of } O_2 \times \text{Molar mass of } O_2 = 0.0345 \text{ moles} \times 32 \text{ g/mol} \approx 1.104 \text{ g} \]

5. **Calculate Total Mass of KClO₃**:
The total mass of potassium chlorate (KClO₃) that decomposes can be calculated using the mass of KCl and the mass of O₂ produced:
\[ \text{Mass of } KClO_3 = \text{Mass of } KCl + \text{Mass of } O_2 = 1.491 \text{ g} + 1.104 \text{ g} = 2.595 \text{ g} \]

6. **Final Answer**:
The mass of potassium chlorate (KClO₃) required to produce the given amounts of KCl and O₂ is approximately:
\[ \text{Mass of } KClO_3 \approx 2.595 \text{ g} \]