Exp 1 Organic Chemistry

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Introduction

Calorimetry is defined as a method to measure a change in thermodynamic quantities. Any processes in which heat is being generated, it is dedicated to calorimetry. Scientists measure the change in thermodynamic quantities in thermochemical equations using a device known as a calorimeter. There are two types of calorimeter which are coffee cup calorimeter and copper calorimeter. This experiment is conducted to apply Hess’s Law which is theoretically learnt during lectures. By doing this experiment, students can see a clearer view in order to apply that particular law. Hess’s Law is saying that if you convert reactants A into products B, the overall enthalpy change will be the same whether you do it in one step or two steps or however many steps. (Jim Clark, 2010.)

Objectives

1. To compare the heat capacities of a coffee cup calorimeter and a copper calorimeter.
2. To determine the standard enthalpy of formation of magnesium oxide, ΔHof

Chemicals

1. 2.0M hydrochloric acid
2. Magnesium oxide powder
3. Magnesium powder

Apparatus

1. 2 thermometer
2. 2 styrofoam cup with cardboard lid
3. 1 copper calorimeter with insulating cover
4. 100cm3 beaker
5. 100cm3 graduated cylinder

Procedures

1. Heat capacity of calorimeter

1. A burette is used to deliver 50cm3 of tap water into the calorimeter. The cover and the thermometer are replaced. The water temperature are recorded for four minutes at one minute interval.
2. 50cm3 of hot water (40 – 50oc above the room temperature) is measured by using a graduated cylinder and is poured into a beaker. Another thermometer is used to record the temperature of hot water and is poured completely into the calorimeter (containing cold water) at the fifth minute. The lid is replaced and the water is stirred with the thermometer. The temperature is recorded every 15 seconds for the next three minutes.
3. Steps (1) and (2) are repeated using the copper calorimeter.

1. Reaction 2 : Magnesium with Hydrochloric Acid

1. 1.0 – 1.1 g of magnesium powder is weighed. The exact weight used is recorded.
2. 50cm3 of 2M HCl is drained from a burette into the calorimeter. The cover and the thermometer are replaced. The temperature of the HCl is recorded every minute for four minutes. At the fifth minute, the magnesium powder is quickly poured into the HCl. The lid is replaced and the mixture is stirred carefully in the calorimeter with the thermometer. The temperature is recorded for the next three minutes at 15 seconds intervals.

1. Reaction 3 : Magnesium Oxide with Hydrochloric Acid

1. 1.6 – 1.8 g of magnesium oxide is weighed. The exact weight used is recorded.
2. Step (2) in (B) is repeated.

Results