# Dissolving: Graph Work

In this worksheet, students will be challenged to take what they have learned about dissolving and set it into the context of an experiment in which they have to interpret the data in terms of graphs.

Key stage:  KS 2

Curriculum topic:   Properties and Changes of Materials

Curriculum subtopic:   Dissolving and Solutions

Difficulty level:

### QUESTION 1 of 10

Mrs. Bates's science class were experimenting on dissolving: they wanted to find out whether the amount of sugar that dissolved in water changed as the temperature increased.

Mrs. Bates gave each group a plastic beaker, a bowl of sugar, a teaspoon, a weighing balance and also 200 ml of water that she had prepared at a particular temperature.

The young scientists then weighed out sugar, adding it to their beaker of water, stirring it until it had all dissolved. They made sure they kept track of the amount of sugar they had added.

When they had all finished and noted down how much sugar they had been able to dissolve in their beaker of water, Mrs. Bates asked for their results which she plotted on this graph:

Before you tackle the following questions, try to imagine you're one of the young scientists in the class and read this through again.

Here is the graph again:

Which temperatures had three groups of students testing how much sugar dissolved in the water?

10, 15, 20, 30

15, 20, 25, 30

15, 25, 30, 35

Mrs. Bates asked the young scientists to copy this graph down into their notebooks:

She then asked them to look at the results for 15oC. One result is much higher than the other two - what do you think might have happened?

The students lost count of the amount of sugar they had added.

The students just kept adding sugar and didn't wait to see if it dissolved.

The students guessed their answers.

Here is the graph they drew:

Next Mrs. Bates asked the class to look at the results for 35oC. One group testing that temperature had a very low result. What do you think might have happened?

The students didn't add enough sugar.

The students added too much sugar.

The students didn't listen carefully to the instructions.

In science experiments it's always better to have as many results as you can. Do you know why this is so?

It makes the results more reliable.

It gives everyone the chance to contribute.

It makes the experiment last longer.

Another thing that is often true of science experiments is that, if you repeat the experiment, the result is unlikely to be EXACTLY the same as the last time.

Why do you think this is?

Every time you do it there will be small differences.

Science experiments usually go wrong.

Most times you do it you'll make a mistake.

Here is the graph again:

Look at the results for 25oC. They are 192 g, 207 g and 211 g. What is the AVERAGE of these three results?

207

203.3

610

Mrs. Bates asked her students to draw a suitable line through the points.

Here is what Aaron did:

Aaron's answer is not correct. Which of the following explanations for what he did wrong is THE LEAST GOOD?

He's simply joined all the dots together.

He hasn't understood why there is more than one point for each temperature.

He should have drawn a single line through the points.

He has connected as many points as possible.

Mrs. Bates's instruction to draw a suitable line through the points led Katy to do this:

Why is Katy's line wrong?

She should have drawn a straight line through the highest points.

She has only joined the highest reading for each temperature.

She should have drawn the line lower down.

Alex listened to Mrs. Bates and then drew this:

What has Alex done?

He has drawn a 'line of best fit' through as many points as possible.

He drew his line through the middle of the points.

He should have drawn his line lower down.

Here is Alex's graph again:

Looking at the graph what do you conclude about the relationship between how the temperature of the water affects how much sugar dissolves in it?

As the temperature increases the amount of sugar that dissolves decreases.

As the temperature increases the amount of sugar that dissolves increases.

As the temperature decreases the amount of sugar that dissolves increases.

• Question 1

Here is the graph again:

Which temperatures had three groups of students testing how much sugar dissolved in the water?

15, 25, 30, 35
EDDIE SAYS
On the graph where there are three points above a temperature - that's three groups of scientists testing that particular temperature.
• Question 2

Mrs. Bates asked the young scientists to copy this graph down into their notebooks:

She then asked them to look at the results for 15oC. One result is much higher than the other two - what do you think might have happened?

The students just kept adding sugar and didn't wait to see if it dissolved.
EDDIE SAYS
This is a toughie - anything might have happened! What is most likely is that they didn't wait to see whether their last spoon of sugar had dissolved - they just stirred and added more which is why their result seems too high.
• Question 3

Here is the graph they drew:

Next Mrs. Bates asked the class to look at the results for 35oC. One group testing that temperature had a very low result. What do you think might have happened?

The students didn't add enough sugar.
EDDIE SAYS
Sure, they may not have listened to the instructions but they definitely haven't added enough sugar! They probably saw a grain of something on the bottom of the beaker and decided that no more sugar would dissolve.
• Question 4

In science experiments it's always better to have as many results as you can. Do you know why this is so?

It makes the results more reliable.
EDDIE SAYS
In science you can NEVER rely on one result from an experiment - in school that one experiment is the only chance you get (there isn't time for more!), but lots of other people have done it before. The more times an experiment is done, the more results you get and then you can see where most of the results are falling and you'll be able to spot the one that doesn't match the general trend.
• Question 5

Another thing that is often true of science experiments is that, if you repeat the experiment, the result is unlikely to be EXACTLY the same as the last time.

Why do you think this is?

Every time you do it there will be small differences.
EDDIE SAYS
OK try this: go and make a perfect glass of Ribena (or orange squash or whatever you like!). Now try to do it again - unless you measure very carefully it's unlikely that you'll be able to get it exactly right again and again. Each time we do something there are small variations, even in the same activity, so the result is slightly different - so... we need lots of results to get an answer we can rely upon.
• Question 6

Here is the graph again:

Look at the results for 25oC. They are 192 g, 207 g and 211 g. What is the AVERAGE of these three results?

203.3
EDDIE SAYS
To find the average add all three together (610) and divide by how many there are (3), so 610/3 = 203.3 g
• Question 7

Mrs. Bates asked her students to draw a suitable line through the points.

Here is what Aaron did:

Aaron's answer is not correct. Which of the following explanations for what he did wrong is THE LEAST GOOD?

He's simply joined all the dots together.
EDDIE SAYS
Aaron has not understood what a scatter graph of the various results is all about - he ought to have drawn his 'line of best fit' - a single line going through as many of the reliable results as possible. However saying that 'he joined the dots' is the least good explanation - that's what you do in a Puzzler magazine!
• Question 8

Mrs. Bates's instruction to draw a suitable line through the points led Katy to do this:

Why is Katy's line wrong?

She has only joined the highest reading for each temperature.
EDDIE SAYS
Katy has ignored the bulk of the results and simply joined the top reading for each temperature - the best line would ignore the wrong readings and join the AVERAGE of the other results at each temperature. That would give the correct line for how much sugar dissolves at each temperature in this experiment.
• Question 9

Alex listened to Mrs. Bates and then drew this:

What has Alex done?

He has drawn a 'line of best fit' through as many points as possible.
EDDIE SAYS
A 'line of best fit' is the line that passes through as many of the correct results as it can - basically it is a line joining the AVERAGE result for each temperature. Strangely it is possible for a line of best fit not to touch any points on the graph at all!
• Question 10

Here is Alex's graph again:

Looking at the graph what do you conclude about the relationship between how the temperature of the water affects how much sugar dissolves in it?

As the temperature increases the amount of sugar that dissolves increases.
EDDIE SAYS
Looking at the graph you can see the results getting higher as you move to the right; that means that as the temperature increases (to the right), more and more sugar is dissolving. For example at 10 C an average of 183.5 g dissolves, at 20 C it's 199 g and at 30 C it's 218 g. Fairly clear!
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