Ideal Gas Law and Magnesium

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UDEC 1124
Chemistry Laboratory 1

Name : Ooi Yan Jie
ID : 1101988
Year and Semester: Y1, S1
Group : 1
Partner’s Name:Lam Meng Hui1101920
Tan Boon Khai1102510
Dang Zien Loong 1102446

Experiment Number: 8
Experiment Title:Determination of the valency of magnesium
Date:29/6/2011
Lecturer:Dr Ha Sie Tiong

Title: Determination of the Valency of Magnesium
Objective
To study the quantitative relationship between the amount of reactants and products of a reaction. A known starting mass of magnesium and the measured collection of hydrogen gas will be used to determine the reaction stoichiometry and the valency of magnesium.

Introduction
Stoichiometry is a measure of relative amount of reactants to products in an experiment. In this experiment, a known mass of magnesium and volume of hydrogen gas collected is used to determine stoichiometry in this experiment.

A known mass of magnesium ribbon is mixed with hydrochloric acid to produce magnesium chloride and hydrogen gas.

Mg(s) + xHCl (l) MgClx (aq) + (x/2)H2(g)

Magnesium will be the limiting factor in this experiment, excess of hydrochloric acid will react completely with magnesium to give hydrogen gas and magnesium chloride. The yield of hydrogen gas is depend on the amount of magnesium used, thus the volume of hydrogen gas collected can be used to determine the x number.

Methodology
1. Burette is used upside down to collect hydrogen gas produced in the experiment. There’s an unknown volume between unmarked space and the tap of burette, the volume is determined by pipette 25.00cm3 of water into the vertically clamped burette  right way up, note the reading, drain the burette and repeat several times.

2. After the unknown volume is measured, leave the 25.00cm3 of water in the burette for around 10 minutes to check whether leaks occur.

3. Magnesium ribbon is cleaned using steel wool. A small piece of magnesium ribbon is cut off and measured accurately on a watch glass within the range 0.0300g to 0.0360g using electrical balance. Both the magnesium ribbon and the watch glass in placed into a 600cm3 beaker.

4. A small filter funnel with a short stem (1.0-1.5cm long) is covered with gauze. It is inverted and placed on the watch glass over the magnesium.

5. Fill in water into the beaker carefully until the water level is approximately 0.5-1.0 cm above the end of the funnel stem. The burette is fully filled with 0.5M HCl, press flat the open end using finger, invert the burette and place it into the water. The finger was removed and place the end of the burette over the stem of the funnel, ensuring no air enter it and clamp the burette in position.

6. Remove excess water using pipette until the water level is just above the stem of the funnel.

7. About 100cm3 of 0.5M HCl is added into the beaker and stirred using a glass rod, to ensure complete mixing. Tapping the watch glass gently to ensure the HCl can enter and react with magnesium.

8. Stir the solution to initiate the reaction but not too further so that the reaction proceeds unaided. At completion of the experiment, the watch glass is tapped to dislodge any hydrogen gas bubbles produced.

Apparatus and Materials

1. Magnesium ribbon ( 0.0300-0.0360 g)
2. Hydrochloric acid (0.5M)
3. Burette (50cm3)
4. Pipette (25cm3)
5. Retort stand
6. Electrical balance
7. Watch glass
8. Beaker (600cm3)
9. Gauze
10. Funnel
11. Glass rod
12. Thermometer

Results

Volume of unmarked space| 9.6 cm3|
Initial reading of burette| 59.6 cm3|
Final reading of burette| 22.4 cm3|
Volume of hydrogen gas| 37.2 cm3|

Calculation
Number of mol of magnesium used = 0.0354g / (24g/mol)
=0.001475 mol

Number of mol of hydrogen gas produced = 37.2cm3 / (24dm3/mol) = 0.00155 mol...
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