PAG 01b- Determination Of The Relative Atomic Mass Of Magnesium

Question 1

Describe how to set up the apparatus to measure volume of gas produced in a reaction.

Answer 1

A gas syringe or upside-down water-filled measuring cylinder in a trough of water may be used to collect the gas

Question 2

What is used to accurately measure mass?

Answer 2

A digital balance that records mass to 2 decimal places

Question 3

Write the chemical equation for the reaction that occurs when magnesium reacts with sulphuric acid.

Answer 3

Mg + H2SO4 -> MgSO4 + H2

Question 4

How can measuring the volume of gas produced during the reaction between magnesium and sulfuric acid be used to determine the relative atomic mass of magnesium?

Answer 4

• Measure mass of some magnesium then react it with sulfuric acid
• Measure volume of hydrogen gas produced in a gas syringe or an upturned water-filled measuring cylinder
• Calculate the number of moles of H2 produced (moles= volume (dm^3) /24)
• Use ratio in chemical equation to find moles of magnesium
• Since original mass of magnesium is known, the relative atomic mass can be calculated by dividing mass by moles

Question 5

Give 2 possible causes of sources in this experiment

Answer 5

• Some hydrogen gas may escape before the bung is put in conical flask
• Some magnesium may not react

Question 6

Why is it important to rapidly put the bung in the conical flask after adding sulfuric acid?

Answer 6

The reaction starts as soon as the acid is added so H2 will start to be produced. To reduce amount of H2 that escapes, the bung should be rapidly inserted.

Question 7

What safety precautions should be taken when conducting an experiment with magnesium and sulfuric acid?

Answer 7

• Sulfuric acid causes skin and eye irritation so wear safety goggles and avoid contact with skin
• Magnesium is highly flammable so keep away from naked flames