Physics » Skills for Science » Scientific Method

# Performing Experiments

## Performing Experiments

A learner wondered whether the rate of evaporation of a substance was related to the boiling point of the substance. Having done background research they realised that the boiling point of a substance is linked to the intermolecular forces within the substance. They know that greater intermolecular forces require more energy to overcome. This led them to form the following hypothesis:

The larger the intermolecular forces of a substance the higher the boiling point. Therefore, if a substance has higher boiling point it will have a slower rate of evaporation.

Perform the following experiment that the learner designed to test that hypothesis.

The boiling points and rate of evaporation experiment is a very simple one meant to introduce the learners to the concept of the scientific method in a practical way. It has been broken up into three parts: performing the practical investigation, analysis of results, drawing conclusions.

The learners should be as accurate as possible when measuring the drop in volume as they will be required to plot a graph of their data.

## Experiment: Boiling Points and Rate of Evaporation Part 1

### Aim

To determine whether the rate of evaporation of a substance is related to its boiling point.

### Apparatus

You will need the following items for this experiment:

• $$\text{220}$$ $$\text{ml}$$ water, $$\text{20}$$ $$\text{ml}$$ methylated spirits, $$\text{20}$$ $$\text{ml}$$ nail polish remover, $$\text{20}$$ $$\text{ml}$$ water, $$\text{20}$$ $$\text{ml}$$ ethanol
• One $$\text{250}$$ $$\text{ml}$$ beaker, four $$\text{20}$$ $$\text{ml}$$ beakers, a thermometer, a stopwatch or clock

### Warning:

All alcohols are toxic, methanol is particularly toxic and can cause blindness, coma or death. Handle all chemicals with care.

1. Place $$\text{200}$$ $$\text{ml}$$ of water into the $$\text{250}$$ $$\text{ml}$$ beaker and move the beaker to sunny spot. Place the thermometer in the water.
2. Label the four $$\text{20}$$ $$\text{ml}$$ beakers $$\text{1}$$$$\text{4}$$. These beakers should be marked.
3. Place $$\text{20}$$ $$\text{ml}$$ methylated spirits into beaker 1, $$\text{20}$$ $$\text{ml}$$ nail polish remover into beaker 2, $$\text{20}$$ $$\text{ml}$$ water into beaker 3 and $$\text{20}$$ $$\text{ml}$$ ethanol into beaker 4. 4. Carefully move each beaker to the warm (sunny) spot.
5. Observe each dish every two minutes. Note the volume in the beaker each time.
6. Continue making observations for $$\text{20}$$ $$\text{minutes}$$. Record the volumes in a table.

### Results

• Record your observations from doing the investigation in a table like the one below.

 Substance Methylated spirits Nail polish remover Water Ethanol Boiling point ($$^{\circ}$$C) $$\text{78.5}$$ $$\text{56.5}$$ $$\text{100}$$ $$\text{78.4}$$ Initial volume (ml) $$\text{20}$$ $$\text{20}$$ $$\text{20}$$ $$\text{20}$$ $$\text{2}$$ $$\text{min}$$ $$\text{4}$$ $$\text{min}$$ $$\text{6}$$ $$\text{min}$$