a. Use the law of conservation of mass to work out the mass of O2 produced. (1 mark)
The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. Thus, the mass of the reactants must equal the mass of the products.
Given:
- Mass of KNO3 = 4.04 g
- Mass of KNO2 produced = 3.40 g
- Let the mass of O2 produced = \( x \).
Using the conservation of mass: \[ \text{Mass of KNO3} = \text{Mass of KNO2} + \text{Mass of O2} \] \[ 4.04 , \text{g} = 3.40 , \text{g} + x \] \[ x = 4.04 , \text{g} - 3.40 , \text{g} = 0.64 , \text{g} \]
Answer: The mass of O2 produced is 0.64 g.
b. Calculate the Mr values of KNO3, KNO2, and O2. (2 marks)
To calculate Mr (molar mass) of each compound:
-
KNO3 (Potassium Nitrate)
- K: 39.10 g/mol
- N: 14.01 g/mol
- O: 3 × 16.00 g/mol = 48.00 g/mol
- Total = 39.10 + 14.01 + 48.00 = 101.11 g/mol
-
KNO2 (Potassium Nitrite)
- K: 39.10 g/mol
- N: 14.01 g/mol
- O: 2 × 16.00 g/mol = 32.00 g/mol
- Total = 39.10 + 14.01 + 32.00 = 85.11 g/mol
-
O2 (Oxygen)
- O: 2 × 16.00 g/mol = 32.00 g/mol
Answer:
- Mr of KNO3 = 101.11 g/mol
- Mr of KNO2 = 85.11 g/mol
- Mr of O2 = 32.00 g/mol
c. Calculate the number of moles of
i. KNO3 (1 mark)
Using the formula: \[ \text{Number of moles} = \frac{\text{mass (g)}}{\text{Mr (g/mol)}} \] \[ \text{Number of moles of KNO3} = \frac{4.04 , \text{g}}{101.11 , \text{g/mol}} \approx 0.0400 , \text{moles} \]
Answer: Moles of KNO3 = 0.0400 moles.
ii. KNO2 (1 mark)
\[ \text{Number of moles of KNO2} = \frac{3.40 , \text{g}}{85.11 , \text{g/mol}} \approx 0.0399 , \text{moles} \]
Answer: Moles of KNO2 = 0.0399 moles.
iii. O2 (1 mark)
Using the mass of O2: \[ \text{Number of moles of O2} = \frac{0.64 , \text{g}}{32.00 , \text{g/mol}} = 0.0200 , \text{moles} \]
Answer: Moles of O2 = 0.0200 moles.
d. Work out the simplest whole number ratio of these values and use this ratio to write a balanced equation for the reaction. (2 marks)
To find the simplest ratio, we divide each number of moles by the smallest number of moles (which is for O2, 0.0200):
\[ \text{KNO3} : \text{KNO2} : \text{O2} = \frac{0.0400}{0.0200} : \frac{0.0399}{0.0200} : \frac{0.0200}{0.0200} = 2 : 2 : 1 \]
Thus, we can write the balanced equation:
\[ 2 , \text{KNO3} \rightarrow 2 , \text{KNO2} + \text{O2} \]
Answer: The simplified ratio is 2:2:1, and the balanced equation is 2 KNO3 → 2 KNO2 + O2.
e. Explain why potassium nitrate is an important component in fireworks.
Potassium nitrate (KNO3) is an important component in fireworks because it acts as an oxidizer. This means it supplies oxygen necessary for the combustion of the fuel present in the fireworks. When heated, potassium nitrate decomposes to release oxygen, which helps to ensure that the other materials can burn effectively. This property allows for the production of loud bangs, colorful displays, and enhances the overall combustion efficiency, making fireworks more explosive and visually appealing. Additionally, potassium nitrate contributes to the bright colors often seen in fireworks due to its ability to produce potassium salts when burned, which create vivid hues in the flame.
Answer: Potassium nitrate is an important component in fireworks because it acts as an oxidizer, supplying oxygen for combustion, enhancing the combustion efficiency and contributing to the colorful displays.
4 answers