# Rate of Dissolving 2

In this worksheet, students will be challenged to consider the factors affecting the rate at which substances dissolve in water.

Key stage:  KS 2

Curriculum topic:   Properties and Changes of Materials

Curriculum subtopic:   Dissolving and Solutions

Difficulty level:

### QUESTION 1 of 10

Many science experiments go at a certain speed, called their 'rate of reaction'. For example if you crack an egg into a frying pan, the rate at which it turns into a fried egg is dependent upon how hot the frying pan is; so temperature is the key factor that determines how long you're going to have to wait for your breakfast!

In this worksheet you are principally going to look at an experiment on sweets and you'll have to decide how important certain factors are in determining how fast the experiment goes.

James was given a packet of sweets called Fizzlers. When he put one of the sweets in water at room temperature it seemed to disappear.

This is because the sweet ___________ in water.

Choose the best word from the list below to fit in the gap:

condenses

evaporates

melts

dissolves

James decided to find out whether STIRRING affected the rate at which one of the Fizzler sweets disappeared in water.

He set up three beakers and filled them to the 30ml mark with water.

Which one of these beakers is closest to the correct amount of water?

 A B C

A

B

C

James put one Fizzler into each of the three beakers and using a spoon he stirred the liquids at different rates, timing how long it took for each sweet to disappear.

Which instrument would be the best choice for James to time his stirring experiment.

clock

stopwatch

thermometer

Once all the sweets had disappeared in the water James took his results and plotted a line graph of them. Here it is:

Use the graph to find out how long it took for the Fizzler to disappear when James stirred it five times per minute.

10mins

2mins

6mins

Once all the sweets had disappeared in the water James took his results and plotted a line graph of them. Here it is:

Use the graph to find out how many stirs per minute James gave the beaker in which the Fizzler took two minutes to disappear.

0 stirs

5 stirs

10 stirs

Now that you've seen James's results, do you think that stirring affected the rate at which the sweet disappeared into the water?

Yes

No

Not sure

Here is James's graph of his results:

Which of the following do you think best explains his results?

the faster James stirred the faster the sweet disappeared

the slower James stirred the faster the sweet disappeared

the faster James stirred the slower the sweet disappeared

James poured 30ml of water into each of his three beakers. Why do you think that was important?

all stirring experiments need 30ml of water

it meant that he could compare his results scientifically

it's a sensible amount of water to use

When James stirred the Fizzler into the beaker of water and it disappeared, he had made Fizzler ___________.

Decide which of the following words is the correct term for what he had made:

solution

suspension

liquid

If James poured a little of his Fizzler mixture in water into a saucer and left it on the windowsill for a week the water would have dried up. What is the best explanation for this?

it evaporated

it boiled away

it disappeared

• Question 1

James was given a packet of sweets called Fizzlers. When he put one of the sweets in water at room temperature it seemed to disappear.

This is because the sweet ___________ in water.

Choose the best word from the list below to fit in the gap:

dissolves
EDDIE SAYS
When things look like they disappear in water they have DISSOLVED which means they break up into tiny, tiny particles you cannot see. They're still there, but really small.
• Question 2

James decided to find out whether STIRRING affected the rate at which one of the Fizzler sweets disappeared in water.

He set up three beakers and filled them to the 30ml mark with water.

Which one of these beakers is closest to the correct amount of water?

 A B C

C
EDDIE SAYS
Look at the scale on the side of the beaker: one says about 75ml, one says over 200ml but the correct one is just over 30ml.
• Question 3

James put one Fizzler into each of the three beakers and using a spoon he stirred the liquids at different rates, timing how long it took for each sweet to disappear.

Which instrument would be the best choice for James to time his stirring experiment.

stopwatch
EDDIE SAYS
James is likely to need seconds as well as minutes (to be accurate in his results) so a stopwatch is more accurate than a clock.
• Question 4

Once all the sweets had disappeared in the water James took his results and plotted a line graph of them. Here it is:

Use the graph to find out how long it took for the Fizzler to disappear when James stirred it five times per minute.

6mins
EDDIE SAYS
Reading along the x (horizontal) axis to the 5 stirs/min line, go up that line to where the diagonal plotted line crosses it and read across to the y (vertical) axis and you'll see it says 6 minutes to disappear.
• Question 5

Once all the sweets had disappeared in the water James took his results and plotted a line graph of them. Here it is:

Use the graph to find out how many stirs per minute James gave the beaker in which the Fizzler took two minutes to disappear.

10 stirs
EDDIE SAYS
Reading along the y (vertical) axis to the 2 min line, go along that line to where the diagonal plotted line crosses it and read down to the x (horizontal) axis and you'll see it says James stirred it 10 times per minute.
• Question 6

Now that you've seen James's results, do you think that stirring affected the rate at which the sweet disappeared into the water?

Yes
EDDIE SAYS
Looking at his results you can see that there's a definite relationship between how many times James stirred his solution and how fast the sweet dissolved: more stirs = less time to dissolve.
• Question 7

Here is James's graph of his results:

Which of the following do you think best explains his results?

the faster James stirred the faster the sweet disappeared
EDDIE SAYS
Clearly, looking at the graph, as James stirs faster the sweet dissolves faster - more stirs = quicker disappearance.
• Question 8

James poured 30ml of water into each of his three beakers. Why do you think that was important?

it meant that he could compare his results scientifically
EDDIE SAYS
You will be well aware of the idea of a 'fair test' - in this experiment James was testing stirring, so he had to keep everything else the same (to keep it 'fair') - that way he could compare his results meaningfully to see whether the only difference (stirring) had had an effect.
• Question 9

When James stirred the Fizzler into the beaker of water and it disappeared, he had made Fizzler ___________.

Decide which of the following words is the correct term for what he had made:

solution
EDDIE SAYS
A suspension is formed when a solid doesn't dissolve in a liquid but mixes with it and slowly settles to the bottom, like mud. If the Fizzler disappears (dissolves) then a SOLUTION has been formed.
• Question 10

If James poured a little of his Fizzler mixture in water into a saucer and left it on the windowsill for a week the water would have dried up. What is the best explanation for this?

it evaporated
EDDIE SAYS
When a solution is left in the open it will slowly EVAPORATE away, meaning that the water leaves the liquid and becomes a gas in the air leaving any solid behind (in this case the particles of Fizzler sweet).
---- OR ----

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