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.  Carefully place the cleaned Mg ribbon into the side arm of the test tube.

6.  Place the rubber stopper onto the test tube.

7.  Record the initial volume of syringe. (Slightly pull the piston of syringe before taking reading)

8.  Tilt the test tube to allow the Mg ribbon fall into the acid.

9.  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.  Data

6.  Calculation

7.  Discussion

8.  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 1

Procedures 3

Calculation

No. of moles of H2(g) produced 1

No. of moles of Mg 1

Relative atomic mass of Mg (correct to 2 d.p.) 1

Discussion 2 Conclusion 1

F 5___ Name: ______( ) Date: ______

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