Magnesium nitrate has completely decomposed into magnesium oxide, nitrogen dioxide gas and oxygen gas when heated at room condition. If 12 g of magnesium nitrate was used in the reaction, calculate
a) The mass of magnesium oxide formed
b) The volume of nitrogen dioxide gas released
[RAM: Mg, 24; N, 14; O, 16]
[Molar volume of gas: 24 dm3mol-1]
Tips:
In solving numerical problems regarding chemical reactions, always:
1. Highlight all the information given in the question.
2. Write a balanced chemical equation of the reaction.
3. Identify the substance that you can find its number of moles.
4. Refer chemical equation for the ratio of moles of substances involved in working your way out to find either their mass, volume or molarity / concentration.
Answer:
a) The mass of magnesium oxide formed
Step 1: Write balanced chemical equation of the reaction
2Mg(NO3)2 → 2MgO ✛ 4NO2 ✛ O2
12 g
Step 2: The number of moles of magnesium nitrate
= Mass / RMM of magnesium nitrate
= 12 g / [24 + 14x2 + 16x6] gmol-1
= 12 g / 148 gmol-1
= 0.081 mol
Step 3: Find the number of moles of magnesium oxide
From chemical equation
2 mol of Mg(NO3)2 produces 2 mol of MgO
Therefore, 0.081 mol of Mg(NO3)2 produces 0.081 mol of MgO
Step 4: Find the mass of magnesium oxide formed
= Number of moles x RMM of magnesium oxide
= 0.081 mol x [24 + 16] gmol-1
= 0.081 mol x 40 gmol-1
= 3.24 g of magnesium oxide
b) The volume of nitrogen dioxide gas released
Step 1: Find the number of moles of nitrogen oxide gas
From chemical equation
2 mol of Mg(NO3)2 produces 4 mol of NO2
Therefore, 0.081 mol of Mg(NO3)2 produces 0.162 mol of NO2
Step 2: Find the volume of nitrogen dioxide gas released
= Number of moles x Molar volume of gas
= 0.162 mol x 24 dm3mol-1
= 3.888 dm3 or 3888 cm3 of nitrogen dioxide gas
Tips:
In solving numerical problems regarding chemical reactions, always:
1. Highlight all the information given in the question.
2. Write a balanced chemical equation of the reaction.
3. Identify the substance that you can find its number of moles.
4. Refer chemical equation for the ratio of moles of substances involved in working your way out to find either their mass, volume or molarity / concentration.
Answer:
a) The mass of magnesium oxide formed
Step 1: Write balanced chemical equation of the reaction
2Mg(NO3)2 → 2MgO ✛ 4NO2 ✛ O2
12 g
Step 2: The number of moles of magnesium nitrate
= Mass / RMM of magnesium nitrate
= 12 g / [24 + 14x2 + 16x6] gmol-1
= 12 g / 148 gmol-1
= 0.081 mol
Step 3: Find the number of moles of magnesium oxide
From chemical equation
2 mol of Mg(NO3)2 produces 2 mol of MgO
Therefore, 0.081 mol of Mg(NO3)2 produces 0.081 mol of MgO
Step 4: Find the mass of magnesium oxide formed
= Number of moles x RMM of magnesium oxide
= 0.081 mol x [24 + 16] gmol-1
= 0.081 mol x 40 gmol-1
= 3.24 g of magnesium oxide
b) The volume of nitrogen dioxide gas released
Step 1: Find the number of moles of nitrogen oxide gas
From chemical equation
2 mol of Mg(NO3)2 produces 4 mol of NO2
Therefore, 0.081 mol of Mg(NO3)2 produces 0.162 mol of NO2
Step 2: Find the volume of nitrogen dioxide gas released
= Number of moles x Molar volume of gas
= 0.162 mol x 24 dm3mol-1
= 3.888 dm3 or 3888 cm3 of nitrogen dioxide gas
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