chemistry question

Question

1.Using a measuring cylinder, add 10 cm3 of ethanol into an insulated 50 cm3 breaker. Measure the temperature of the liquid.
2.add 20 cm3 of cyclohexane to the ethanol in the breaker, mix well and record the lowest temperature of the liquid
Explain why cyclohexane has to be used in excess in this experiment
Comment on the reliability of the hydrogen bond strength obtained.

Answer 1

Explain why cyclohexane has to be used in excess in this experiment

Before mixing, ethanol molecules are held together by hydrogen bonds, while cyclohexane molecules are held together by van der Waals’ forces.

Since cyclohexane molecules are quite large in size, the addition of cyclohexane molecules would break the hydrogen bonds between the ethanol molecules, and heat is absorbed from the liquid mixture. This experiment is to estimate the strength of hydrogen bonds between ethanol molecules. Therefore, excess cyclohexane is used because this is to ensure that all hydrogen bonds between ethanol molecules are broken.

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Comment on the reliability of the hydrogen bond strength obtained.

That means you have to discuss the error of the experiment. i.e.

1. Heat gain from the surroundings is the major error.

2. There are errors in reading temperature.

3. Measuring cylinders are used to measure the volumes of liquids. Such instrument is not accurate enough.

etc.