When magnesium nitrate(V) is heated, it decomposes to form magnesium oxide, nitrogen(IV) oxide and oxygen - CIE - A-Level Chemistry - Question 1 - 2014 - Paper 1

From the balanced equation, we can observe the molar ratios:

• 2 moles of magnesium nitrate produce 2 moles of magnesium oxide, 4 moles of nitrogen(IV) oxide, and 1 mole of oxygen.

Given that 1 mole of magnesium nitrate produces:

• Magnesium Oxide: 1 mole
• Nitrogen(IV) Oxide: 2 moles
• Oxygen: 0.5 moles

Mass of magnesium oxide produced: $1 ext{ mole} \times 24.3 ext{ g/mol} = 24.3 ext{ g}$

Volume of nitrogen(IV) oxide produced: $2 ext{ moles} \times 24 ext{ dm}^3 = 48.0 ext{ dm}^3$

Volume of oxygen produced: $0.5 ext{ moles} \times 24 ext{ dm}^3 = 12.0 ext{ dm}^3$

The experimental set-up would consist of:

1. A directly heated vessel labeled "magnesium nitrate(V)" with a tube at exit.
2. A gas stream led into a liquid-filled container with a labeled alkali to absorb nitrogen(IV) oxide.
3. A gas collection device (syringe or liquid container) for collecting oxygen separately.
4. Ensure all connections are airtight, and the nitrogen(IV) oxide absorption occurs before oxygen collection.

For a gas collector with a capacity suitable for 12.0 dm³ of oxygen: The mass of magnesium nitrate(V) required to produce this volume of oxygen (since 0.5 moles of oxygen corresponds to 1 mole of magnesium nitrate):

$0.5 \text{ moles} \times 2 = 1\text{ mole of magnesium nitrate(V)}$

Mass of magnesium nitrate(V): $1 \text{ mole} \times 148.3 \text{ g/mol} = 148.3 ext{ g}$

The measurements would include:

• Mass of magnesium nitrate(V) before heating.
• Mass of magnesium oxide after heating.
• Volume of oxygen produced.
• Volume of nitrogen(IV) oxide absorbed by the alkali.
• Temperature of the reaction.

To confirm that magnesium nitrate(V) had completely decomposed, one can:

• Measure the mass of the products; if the mass of the magnesium oxide remains constant after further heating, then decomposition is complete.
• Analyze the gases collected to ensure all expected volumes of nitrogen(IV) oxide and oxygen are present.

Before taking measurements, ensure:

• The apparatus is at room temperature to avoid gas expansions or contractions affecting the volume readings.
• Any air leaks are sealed, and the apparatus is functioning properly. Allowing the gas to stabilize before measurement is crucial.

To confirm the decomposition occurred according to the molar ratios, one would:

• Compare the measured volumes of gases collected with the theoretical volumes calculated from the balanced equation.
• The ratio of the volumes of gases (oxygen to nitrogen(IV) oxide) should reflect the coefficients in the balanced equation. Consistency with these ratios indicates the reaction proceeded correctly.

Safety precautions would include:

• Wearing appropriate personal protective equipment (PPE) like gloves and goggles.
• Conducting the experiment in a fume hood to avoid inhaling nitrogen(IV) oxide.
• Ensuring all reagents are handled with care and that there is adequate ventilation in the laboratory.