# Evaluating Scientific Investigations

In this worksheet, students will practise the evaluation of their experimental methods when doing their controlled assessment.

Key stage:  KS 4

Curriculum topic:  Working Scientifically: Scientific Thinking

Curriculum subtopic:  Evaluating Risks

Difficulty level:

### QUESTION 1 of 10

In this worksheet you will be presented with a series of experimental methods and you will be asked to evaluate the method by spotting a mistake or something that is incomplete.

You should do your own research on the internet to find similar experiments.

Measuring the concentration of oxygen in the air

The pie chart shows the gas content in the Earth's atmosphere. Oxygen takes up 21%.

Some pupils want to investigate this and see for themselves if the air oxygen content around them is around 1/5 of the whole air volume.

The group of pupils planned their investigation as follows:

1. Moisten a piece of steel wool and place it at the bottom of a measuring cylinder.

2. Turn the cylinder upside down and immerse the open end in a beaker of water.

3. Let the oxygen be removed from the air sample. This may take several days.

4. Every day measure the air sample volume by reading the scale of the measuring cylinder.

Evaluate the pupils' method.

It is not clear how to achieve water entering the tube, which is needed to measure the volume of oxygen.

The pupils do not make it clear how to let oxygen be removed from the air sample.

It is not clear how to measure the air sample volume.

Hooke's Law

Some pupils set up an experiment to test Hooke's Law, which states that a material will extend in proportion to the force applied to it. Here is their method.

Experimental method

1. Hang a spring.

2. Hang masses from the spring and measure the extension.

3. Then plot your results in a graph.

Identify two problems with the method.

It is not specified where to hang the spring from.

Step 3 is too general.

Step 2 should be explained more, i.e. springs must be hung one by one, and measure the extension of every spring.

It is not specified what type of spring to use.

Candle burning 1

Experimental method

1. Light a candle and invert a beaker over it.

2. As soon as the beaker is inverted, start the timer.

3. As soon as the candle is extinguished, stop the timer.

4. Record the time in a table of results.

5. Repeat the experiment with beakers of different volumes.

Choose the statement that shows a problem with this method - either in a practical way or the way it is presented.

It is not specified why you need to use beakers of different volumes.

The method is too specific when to turn the timer on and off.

It is not necessary to record results in a table.

Candle burning 2

Experimental method

1. Light a candle and invert a beaker over it.

2. As soon as the beaker is inverted, start the timer.

3. As soon as the candle is extinguished, stop the timer.

4. Record the time in a table of results.

5. Repeat the experiment with beakers of different volumes.

Choose another statement that shows a problem with this method - either in a practical way or the way it is presented.

A beaker does not allow extra oxygen to enter.

Beakers have a lip, which allows air to enter, so the volume of the beaker is not accurate.

The method states explicitly when to start the timer.

Candle burning 3

Experimental method

1. Light a candle and invert a beaker over it.

2. As soon as the beaker is inverted, start the timer.

3. As soon as the candle is extinguished, stop the timer.

4. Record the time in a table of results.

5. Repeat the experiment with beakers of different volumes.

Identify a risk with this method.

breaking the timer while using it

spilling acid on the work surface

There is a risk of burning your skin from the hot container and candle.

Candle burning 4

Experimental method

1. Light a candle and invert a beaker over it.

2. As soon as the beaker is inverted, start the timer.

3. As soon as the candle is extinguished, stop the timer.

4. Record the time in a table of results.

5. Repeat the experiment with beakers of different volumes.

How can you manage the risk of burning your skin from the hot container and candle?

wear goggles

allow time for the container to cool down and the wax to solidify before changing to the next candle

use a heat proof mat

Candle burning 5

Experimental method

1. Light a candle and invert a beaker over it.

2. As soon as the beaker is inverted, start the timer.

3. As soon as the candle is extinguished, stop the timer.

4. Record the time in a table of results.

5. Repeat the experiment with beakers of different volumes.

How can you manage the risk of damaging the surface you are working on?

wear goggles

allow time for the container to cool down and the wax to solidify before changing to the next candle

use a heat-proof mat

Rate of reaction 1

The diagram shows how to set up an experiment to measure the rate of the reaction between hydrochloric acid and magnesium.

Identify a possible risk with this experiment.

spilling the acid and damaging the surface as well as your eyes

putting too much acid in there

using the wrong type of magnesium

Rate of reaction 2

Identify a second possible risk with this experiment.

The stand is too high for the delivery tube to be in the correct place in the trough.

The trough is too big.

The delivery tube is made of thin glass and can break easily.

Rate of reaction 3

How could you manage the risk of breaking the measuring cylinder? Choose two options.

You could use a plastic measuring cylinder.

You could place it higher up away from the rest of the equipment.

You could fix it very tightly in the clamp so it doesn't fall.

You need to be careful not to tighten the clamp too much.

• Question 1

Measuring the concentration of oxygen in the air

The pie chart shows the gas content in the Earth's atmosphere. Oxygen takes up 21%.

Some pupils want to investigate this and see for themselves if the air oxygen content around them is around 1/5 of the whole air volume.

The group of pupils planned their investigation as follows:

1. Moisten a piece of steel wool and place it at the bottom of a measuring cylinder.

2. Turn the cylinder upside down and immerse the open end in a beaker of water.

3. Let the oxygen be removed from the air sample. This may take several days.

4. Every day measure the air sample volume by reading the scale of the measuring cylinder.

Evaluate the pupils' method.

It is not clear how to achieve water entering the tube, which is needed to measure the volume of oxygen.
EDDIE SAYS
Pupils do not make it clear how to turn the cylinder upside down into the beaker of water. They have to specify that water must enter the boiling tube, in order to be able to measure the volume change.
• Question 2

Hooke's Law

Some pupils set up an experiment to test Hooke's Law, which states that a material will extend in proportion to the force applied to it. Here is their method.

Experimental method

1. Hang a spring.

2. Hang masses from the spring and measure the extension.

3. Then plot your results in a graph.

Identify two problems with the method.

It is not specified where to hang the spring from.
Step 2 should be explained more, i.e. springs must be hung one by one, and measure the extension of every spring.
EDDIE SAYS
If pupils perform the method as stated, they may end up hanging all springs at the same time, which will not help investigate Hooke's Law.
• Question 3

Candle burning 1

Experimental method

1. Light a candle and invert a beaker over it.

2. As soon as the beaker is inverted, start the timer.

3. As soon as the candle is extinguished, stop the timer.

4. Record the time in a table of results.

5. Repeat the experiment with beakers of different volumes.

Choose the statement that shows a problem with this method - either in a practical way or the way it is presented.

It is not specified why you need to use beakers of different volumes.
EDDIE SAYS
This method does not specify why you need to use beakers of different volumes. In order to gain maximum marks, you have to explain that using beakers of different volumes will help you investigate how different volumes of oxygen affect the time the candle burns for.
• Question 4

Candle burning 2

Experimental method

1. Light a candle and invert a beaker over it.

2. As soon as the beaker is inverted, start the timer.

3. As soon as the candle is extinguished, stop the timer.

4. Record the time in a table of results.

5. Repeat the experiment with beakers of different volumes.

Choose another statement that shows a problem with this method - either in a practical way or the way it is presented.

Beakers have a lip, which allows air to enter, so the volume of the beaker is not accurate.
EDDIE SAYS
Beakers have a lip, which allows air to enter, so the volume of the beaker is not accurate. For example, the 100 ml beaker will not have 100 ml of air, as more air would enter from the lip.
• Question 5

Candle burning 3

Experimental method

1. Light a candle and invert a beaker over it.

2. As soon as the beaker is inverted, start the timer.

3. As soon as the candle is extinguished, stop the timer.

4. Record the time in a table of results.

5. Repeat the experiment with beakers of different volumes.

Identify a risk with this method.

There is a risk of burning your skin from the hot container and candle.
EDDIE SAYS
There is a risk of burning your skin from the hot container and candle. Think about how to manage this risk to answer the next question.
• Question 6

Candle burning 4

Experimental method

1. Light a candle and invert a beaker over it.

2. As soon as the beaker is inverted, start the timer.

3. As soon as the candle is extinguished, stop the timer.

4. Record the time in a table of results.

5. Repeat the experiment with beakers of different volumes.

How can you manage the risk of burning your skin from the hot container and candle?

allow time for the container to cool down and the wax to solidify before changing to the next candle
EDDIE SAYS
You must allow time for the container to cool down and the wax to solidify before changing to the next candle. Make sure you clearly state how to manage risks in your method.
• Question 7

Candle burning 5

Experimental method

1. Light a candle and invert a beaker over it.

2. As soon as the beaker is inverted, start the timer.

3. As soon as the candle is extinguished, stop the timer.

4. Record the time in a table of results.

5. Repeat the experiment with beakers of different volumes.

How can you manage the risk of damaging the surface you are working on?

use a heat-proof mat
EDDIE SAYS
A heat-proof mat must be used every time you do an experiment with fire to protect your working surface. This will also help to stop a fire from spreading.
• Question 8

Rate of reaction 1

The diagram shows how to set up an experiment to measure the rate of the reaction between hydrochloric acid and magnesium.

Identify a possible risk with this experiment.

spilling the acid and damaging the surface as well as your eyes
EDDIE SAYS
There is a danger of spilling the acid and damaging the surface as well as your eyes, so one needs to wear goggles at all times and be careful when handling the acid.
• Question 9

Rate of reaction 2

Identify a second possible risk with this experiment.

The delivery tube is made of thin glass and can break easily.
EDDIE SAYS
The delivery tube is made of thin glass and can break easily. One must be very careful when handling it and make sure pressure is not applied.
• Question 10

Rate of reaction 3

How could you manage the risk of breaking the measuring cylinder? Choose two options.

You could use a plastic measuring cylinder.
You need to be careful not to tighten the clamp too much.
EDDIE SAYS
You could use a plastic measuring cylinder or be careful not to tighten the clamp too much. The measuring cylinder must be fixed properly in the clamp, but too much pressure will break it and that may cause injury.
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