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Experiment 1: Determination of the Formula Unit

SK015 Chemistry Lab Manual

Objectives

  • Synthesise a zinc chloride compound.
  • Determine the formula unit of zinc chloride.

Introduction

A quantitative analysis can be used to determine the composition of an unknown compound. In this experiment, a compound composed of zinc and chlorine will be prepared. By measuring the masses of the reactants and products, the mole ratio and percentage composition can be deduced to identify the formula unit.

Chemical Reagents & Apparatus

  • Reagents:
  • • 6 M HCl Solution
  • • Zinc Powder
  • Apparatus:
  • • Analytical Balance
  • • Hot Plate
  • • Crucible & Cover

Experimental Procedure & Data Recording

1

Weigh the crucible and approximately 0.25g of Zinc powder.

2

Add 10 mL of 6 M HCl. Heat the content slowly on a hot plate until completely dry.

CAUTION: Carry out this step in a fume cupboard. Avoid overheating to prevent product melting.
3

Allow to cool. Reheat until the difference in mass does not exceed 0.02 g (Constant Mass).

Quantitative Analysis Results

Data Summary

1. Mass of empty crucible: 0.0000 g
2. Mass of crucible + zinc: 0.0000 g
3. Mass of zinc powder: 0.0000 g
4.1 Mass (First heating): 0.0000 g
4.2 Mass (Second heating): 0.0000 g
4.3 Mass (Third heating): 0.0000 g
5. Mass of zinc chloride: 0.0000 g
6. Mass of chlorine: 0.0000 g

Formula Deduction

Mol Zn: 0.0000

Mol Cl: 0.0000

Simplest Ratio Zn:Cl ≈ 1 : 2

Determined Formula Unit

ZnCl₂

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Exp 1: Zinc Chloride

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