F5 Chemistry Experiment
Determination of relative atomic mass of magnesium by measuring the volume of H2 produced
Apparatus
Gas syringe, rubber stopper, electronic balance, sand paper, side-arm flask
Procedures (suggested)
1. Clean the Mg ribbon with sand paper.
2. Weigh the cleaned Mg ribbon (m1 g).
3. Add excess known volume dilute HCl(aq) into side-arm test tube
4. Connect the gas syringe to the side-arm test tube.
5.
6.
7.
8.
9.
Carefully place the cleaned Mg ribbon into the side arm of the test tube.
Place the rubber stopper onto the test tube.
Record the initial volume of syringe. (Slightly pull the piston of syringe before taking reading)
Tilt the test tube to allow the Mg ribbon fall into the acid.
Record the volume of H2(g) produced after Mg ribbon is completely dissolved. (Slightly pull the
piston of syringe before taking reading)
10. Record the indoor temperature.
Data
Mass of cleaned Mg ribbon = m1 g
Volume of HCl used = x cm3
Molarity of HCl used = a mol dm3
Volume of H2(g) produced = V cm3
Indoor temperature = T C
Calculation
Mg(s) + 2H+(aq)  Mg2+(aq) + H2(g)
No. of moles of H2(g) produced = (V / 1000) / 24.0 = (a)
No. of moles of Mg ribbon = (a)
Relative atomic mass of Mg = m1 / (a) (correct to 2 d.p.)
Discussion
Q1. Sources of errors of the experiment (at least 2)
Ans: Mg ribbon is not well cleaned / impurities on Mg ribbon / incorrect measurement of the volume
of H2(g) produced / the indoor temperature is not exactly 298 K / molar volume should not be
24.0 dm3
Q2. How to improve the experiment
Ans: Clean the Mg ribbon carefully / use fresh Mg ribbon / repeat the experiment / measure the
temperature inside the side arm test tube / the side arm test tube is immersed in a water bath at 25 oC
Guidelines on writing reports
The report should contain:
1. Date
2. Title of experiment
3. Objective
4. Procedures
5.
6.
7.
8.
Data
Calculation
Discussion
Conclusion
SBA experiment
1. Each group of 10 students is allowed to conduct the SBA experiment determination of relative
atomic mass of Mg) within 15 mins. (20 mins for the first group)
2. After finishing the SBA experiment, the 10 students should hand in the data sheet, including the
calculation, within 10 mins.
3. For those students who have submitted the data sheet, or waiting for the SBA experiment, they
should conduct another experiment (Investigate the properties of HCl and CH3COOH).
2 students a group.
Allocation of marks of full report (suggested)
(Max 10 marks)
Date, Introduction, Objective
Procedures
Calculation
1
3
No. of moles of H2(g) produced
No. of moles of Mg
Relative atomic mass of Mg (correct to 2 d.p.)
Discussion
Conclusion
1
1
1
2
1
F 5___ Name: ______________________(
)
Data Sheet
Chemical equation:
Data
Mass of cleaned Mg ribbon / g
Volume of HCl used / cm3
Molarity of HCl used / mol dm3
Volume of H2(g) produced / cm3
Indoor temperature / C
Calculations
(Given: Molar volume of gas at room temperature and pressure = 24.0 dm3)
No. of moles of H2(g) produced
No. of moles of Mg ribbon
Relative atomic mass of Mg
Date: ____________