# Evaluate Scientific Investigations

In this worksheet, students will practise evaluating their experimental methods when carrying out their controlled assessment.

Key stage:  KS 3

Curriculum topic:   Working Scientifically

Curriculum subtopic:   Scientific Attitudes

Difficulty level:

### QUESTION 1 of 10

In this worksheet, you will be presented with a series of experimental methods

You will then be asked to evaluate the method by identifying any mistakes or something that is incomplete.

It is important to evaluate methodology as this so that you can identify any problems or weaknesses that can be rectified (corrected) for later experiments. It makes you a stronger scientist!

You could also do your own internet research to find similar experiments to get a better idea of different methods!

Now it's over to you.

How do we go about 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 if the air oxygen content around them is really 1/5 of the entire 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. Remove oxygen 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.

The pupils don't make it clear how they intend to turn the cylinder upside down in the water in order to collect an oxygen sample

The pupils don't make it clear how oxygen will be removed from the air sample

It's not clear how to measure the air sample volume

How would you test Hooke's law?

Some pupils set up an experiment to test Hooke's Law.

Hooke's law states that material will extend in proportion to the force applied to it.

Here is their experimental method:

1. Hang a spring.

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

3. Plot your results in a graph.

Identify two problems with the method above.

It's not specified at what point to hang the spring from

Step 3 is too vague

Step 2 should be explained with clearer instructions i.e. each spring must be hung individually then each extension should be measured

It's not specified what type of spring will be used

Some pupils decide to perform a candle burning experiment, look at their plan below.

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 between step 2 and 3 in a table of results.

5. Repeat the experiment with beakers of different volumes.

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

It's 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's not necessary to record results in a table

Look at the experimental method below. The pupils attempted to improve the method you read in the previous question.

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 sense or the way it is written.

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

Look at the same experimental method once more.

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 the candle

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 could you manage the risk of burning your skin on the hot container and candle?

By wearing goggles

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

By using a heat proof mat

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?

By wearing goggles

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

By using a heat-proof mat

How would you test the rate of reaction?

The diagram below shows how you would set up an experiment that measures 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 the container

Using the wrong type of magnesium

The diagram below is the same as the last question.

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

Look at the same diagram below.

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 would be careful not to tighten the clamp too much

• Question 1

How do we go about 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 if the air oxygen content around them is really 1/5 of the entire 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. Remove oxygen 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.

The pupils don't make it clear how they intend to turn the cylinder upside down in the water in order to collect an oxygen sample
EDDIE SAYS
Pupils do not make it clear how to turn the cylinder upside down into the beaker of water. They needed to specify that water must enter the boiling tube, in order to be able to measure the volume change. This was a challenging start, but it is this kind of vagueness in your investigation plan that you must avoid!
• Question 2

How would you test Hooke's law?

Some pupils set up an experiment to test Hooke's Law.

Hooke's law states that material will extend in proportion to the force applied to it.

Here is their experimental method:

1. Hang a spring.

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

3. Plot your results in a graph.

Identify two problems with the method above.

It's not specified at what point to hang the spring from
Step 2 should be explained with clearer instructions i.e. each spring must be hung individually then each extension should be measured
EDDIE SAYS
If pupils perform the method as stated, they risk hanging all springs at the same time, which would not be an effective way of investigating Hooke's Law. The experiment lacks a precise description, leaving too much room for error. Is this becoming less daunting?
• Question 3

Some pupils decide to perform a candle burning experiment, look at their plan below.

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 between step 2 and 3 in a table of results.

5. Repeat the experiment with beakers of different volumes.

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

It's 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 must explain that using beakers of different volumes enables you to investigate how different volumes of oxygen impact the time the candle burns for. In this way, your methodology will identify what variable you are changing.
• Question 4

Look at the experimental method below. The pupils attempted to improve the method you read in the previous question.

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 sense or the way it is written.

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 an accurate measurement. For example, an 100 ml beaker will not have 100 ml of air, as more air would enter from the lip. Did you spot that?
• Question 5

Look at the same experimental method once more.

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 the candle
EDDIE SAYS
There is a risk in this experiment of burning your skin on the hot container and candle. Think about how best to manage this risk? You want to be as safe as possible when carrying out your investigations.
• Question 6

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 could you manage the risk of burning your skin on the hot container and candle?

By allowing 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 to clearly state how you intend to manage risks in your method as this demonstrates great foresight!
• Question 7

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?

By using a heat-proof mat
EDDIE SAYS
A heat-proof mat must be used every time you do an experiment with a flame in order to protect your working surface. This will also help to stop any potential fire from spreading!
• Question 8

How would you test the rate of reaction?

The diagram below shows how you would set up an experiment that measures 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 (more importantly!). So one needs to wear goggles at all times and be especially careful when handling the acid.
• Question 9

The diagram below is the same as the last question.

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, ensuring too much pressure is not applied. You're making great progress!
• Question 10

Look at the same diagram below.

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

You could use a plastic measuring cylinder
You would be careful not to tighten the clamp too much
EDDIE SAYS
The correct answers were either using a plastic measuring cylinder or, being 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 on the scientist! Great focus, that's another activity completed!
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