What mass of potassium chlorate (`KClO_3`) on heating gives 1.951 g of potassium chloride (KCl) and 0.672 litres of oxygen at NTP?

Options

A. 1.591g
B. 2.911g
C. 1.951g
D. None

Explanation

To determine the mass of potassium chlorate (KClO₃) that decomposes to give 1.951 g of potassium chloride (KCl) and 0.672 liters of oxygen at NTP, we can follow these steps:

### Step 1: Write the balanced chemical equation for the decomposition of potassium chlorate.

The decomposition reaction of potassium chlorate is as follows:

\[ 2 \text{KClO}_3 \rightarrow 2 \text{KCl} + 3 \text{O}_2 \]

### Step 2: Calculate the number of moles of oxygen produced.

At NTP (Normal Temperature and Pressure), 1 mole of a gas occupies 22.4 liters. To find the number of moles of oxygen produced from 0.672 liters, we use the formula:

\[ \text{Number of moles of } O_2 = \frac{\text{Volume of } O_2}{\text{Molar volume at NTP}} = \frac{0.672 \text{ L}}{22.4 \text{ L/mol}} \]

Calculating this gives:

\[ \text{Number of moles of } O_2 = \frac{0.672}{22.4} = 0.03 \text{ moles} \]

### Step 3: Determine the moles of KCl produced.

From the balanced equation, we see that 2 moles of KClO₃ produce 2 moles of KCl. Therefore, the number of moles of KCl produced is equal to the number of moles of KClO₃ decomposed. Since 2 moles of KCl are produced for every 2 moles of KClO₃, we can conclude that:

\[ \text{Moles of KCl} = \text{Moles of KClO}_3 \]

### Step 4: Calculate the mass of oxygen produced.

The molar mass of oxygen (O₂) is 32 g/mol. To find the mass of 0.03 moles of oxygen, we use the formula:

\[ \text{Mass of } O_2 = \text{Number of moles} \times \text{Molar mass} = 0.03 \text{ moles} \times 32 \text{ g/mol} = 0.96 \text{ g} \]

### Step 5: Calculate the total mass of KClO₃ decomposed.

The total mass of KClO₃ that decomposed can be calculated using the mass of KCl produced and the mass of oxygen produced:

\[ \text{Mass of KClO}_3 = \text{Mass of KCl} + \text{Mass of } O_2 \]

Substituting the values we have:

\[ \text{Mass of KClO}_3 = 1.951 \text{ g} + 0.96 \text{ g} = 2.911 \text{ g} \]

### Final Answer:

The mass of potassium chlorate (KClO₃) that decomposes to give the specified products is **2.911 g**.

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