The smart way to improve grades

Comprehensive & curriculum aligned

Affordable pricing from £10/month

Separating Substances: Step-by-Step 2

In this worksheet, students will be helped to understand the importance of carrying out the steps of an experiment (here separating rock salt) in the correct order.

'Separating Substances: Step-by-Step 2' worksheet

Key stage:  KS 2

Curriculum topic:  Properties and Changes of Materials

Curriculum subtopic:  Separating Mixtures

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

 Rock salt is natural salt that is dug out of the ground. In the UK there are salt mines in Cheshire and much of this salt is crushed and used to 'grit' the roads in winter when they have ice and snow on them, helping to keep them clear. Rock salt is the remains of prehistoric seas and is a mixture of salt together with sand and rock.

 

Rock salt

 

In the first experiment, Robert is trying to extract some pure salt from a lump of rock salt; he is hoping that he will have enough to sprinkle on his fish and chips!

First of all Robert took the lumps of rock salt his teacher had given him and started to crush them up using a pestle and mortar (like in the picture).

 

Pestle and mortar

 

Why do you think that he started by crushing the rock salt up?

So it would be easier to pour

So it would dissolve more quickly in water

So he would be able to see the bits of salt

After he had crushed it, Robert stirred the rock salt into some water.

 

Stirring a solution

 

Why do you think he did this?

He wanted to dissolve the salt

He wanted to mix them all together

The experiment only works in water

Once he had stirred the rock salt into the water, he carefully poured his mixture into some filter paper in a funnel.

Filtering a solution

 

What do you think he saw dripping out of the filter paper?

pink liquid

white liquid

colourless liquid

Robert took the liquid he had extracted from his filtered rock salt and poured it into an evaporating dish.

 

 Evaporation

 

He heated the liquid gently. After a few minutes he saw some white crystals appearing in the dish as the water evaporated away. What do you think the white crystals were made of?

pure sand

salt

sugar

Molly and Lucy were experimenting on sugars. They had both GRANULATED SUGAR (which has bigger grains) and CASTER SUGAR (which has smaller grains).

 

Granulated sugar Caster sugar
GRANULATED CASTER

 

What they wanted to find out is whether the size of the grains affected how quickly the sugar dissolved in water.

First Molly stirred 20g of granulated sugar into 100ml of warm water and timed how long it took to dissolve - it took 50 seconds.

Next Lucy stirred 20g of caster sugar into 100ml of warm water and found that it took 20 seconds to dissolve.

 

Which instrument do you think is the best choice for them to use to time how long it took the sugar to dissolve?

clock

stopwatch

thermometer

Here are Molly and Lucy's results again:

TYPE OF SUGAR  AMOUNT/g AMOUNT OF WATER/ml TIME TAKEN TO DISSOLVE/sec
Granulated 20 100 50
Caster 20 100 20

 

From these results what do you think Molly and Lucy concluded about the effect of the size of the grains of sugar on how fast they dissolved in water?

grain size doesn't affect the rate of dissolving

smaller grains dissolve faster

bigger grains dissolve faster

What do you think that Molly and Lucy could do in their experiments to make their results more reliable?

do more experiments

repeat the same test several times

try with different sugars (like icing sugar)

Why do you think that Molly and Lucy both used the same amount of sugar and warm water in their tests?

so they could compare their results

they could only measure up to 100ml water

20g of sugar was the most they could dissolve

Molly and Lucy used 'warm water' in their tests. What would they be better using in any future experiments on dissolving?

hot water

cold water

water of a known temperature

  • Question 1

First of all Robert took the lumps of rock salt his teacher had given him and started to crush them up using a pestle and mortar (like in the picture).

 

Pestle and mortar

 

Why do you think that he started by crushing the rock salt up?

CORRECT ANSWER
So it would dissolve more quickly in water
EDDIE SAYS
With big lumps crushing makes a big difference: when you stir the crushed mixture into the water, the liquid can work at dissolving all of it at once. With big lumps it takes ages for the water to dissolve all the outside layers in order to get to the middle.
  • Question 2

After he had crushed it, Robert stirred the rock salt into some water.

 

Stirring a solution

 

Why do you think he did this?

CORRECT ANSWER
He wanted to dissolve the salt
EDDIE SAYS
The clever thing with Robert's experiment is that the water will dissolve the salt but not the sand and rock - at this point they begin to separate.
  • Question 3

Once he had stirred the rock salt into the water, he carefully poured his mixture into some filter paper in a funnel.

Filtering a solution

 

What do you think he saw dripping out of the filter paper?

CORRECT ANSWER
colourless liquid
EDDIE SAYS
The filter separates the sand and rock (which get trapped) from the salt solution (which passes through). When salt dissolves in water it 'disappears' (although the salt remains as tiny tiny particles in the liquid), so the liquid is colourless.
  • Question 4

Robert took the liquid he had extracted from his filtered rock salt and poured it into an evaporating dish.

 

 Evaporation

 

He heated the liquid gently. After a few minutes he saw some white crystals appearing in the dish as the water evaporated away. What do you think the white crystals were made of?

CORRECT ANSWER
salt
EDDIE SAYS
Remember that when salt (or any solid) dissolves in water it divides up into tiny particles but ... IT STAYS AS A SOLID! That means that when the water evaporates away all the solid stays behind (just like fish in a pond as the water level gets lower and lower in hot weather).
  • Question 5

Molly and Lucy were experimenting on sugars. They had both GRANULATED SUGAR (which has bigger grains) and CASTER SUGAR (which has smaller grains).

 

Granulated sugar Caster sugar
GRANULATED CASTER

 

What they wanted to find out is whether the size of the grains affected how quickly the sugar dissolved in water.

First Molly stirred 20g of granulated sugar into 100ml of warm water and timed how long it took to dissolve - it took 50 seconds.

Next Lucy stirred 20g of caster sugar into 100ml of warm water and found that it took 20 seconds to dissolve.

 

Which instrument do you think is the best choice for them to use to time how long it took the sugar to dissolve?

CORRECT ANSWER
stopwatch
EDDIE SAYS
Since they need something that reads fairly accurately in seconds, a stopwatch is a better choice than a clock.
  • Question 6

Here are Molly and Lucy's results again:

TYPE OF SUGAR  AMOUNT/g AMOUNT OF WATER/ml TIME TAKEN TO DISSOLVE/sec
Granulated 20 100 50
Caster 20 100 20

 

From these results what do you think Molly and Lucy concluded about the effect of the size of the grains of sugar on how fast they dissolved in water?

CORRECT ANSWER
smaller grains dissolve faster
EDDIE SAYS
It's clear from their results that caster sugar, with the smaller grain size, dissolves much quicker than granulated sugar. Because the water doesn't have to dissolve the grains in layers, bit by bit, and can pretty much dissolve it all at once, smaller grains of anything dissolve faster.
  • Question 7

What do you think that Molly and Lucy could do in their experiments to make their results more reliable?

CORRECT ANSWER
repeat the same test several times
EDDIE SAYS
Scientists never go big with a conclusion after just one experiment: they do the same test again and again, making sure that they always get the same result. It's so easy for things to go wrong they want to make sure they've covered everything.
  • Question 8

Why do you think that Molly and Lucy both used the same amount of sugar and warm water in their tests?

CORRECT ANSWER
so they could compare their results
EDDIE SAYS
By keeping their quantities of water and sugar the same it meant they could compare their results; this is the basis of a 'fair test'. If Molly had added 100g of sugar the results would have been completely different and they couldn't have compared them meaningfully.
  • Question 9

Molly and Lucy used 'warm water' in their tests. What would they be better using in any future experiments on dissolving?

CORRECT ANSWER
water of a known temperature
EDDIE SAYS
It's all about being able to repeat your experiments to check your results: how hot is 'warm' water? Depends on how cold your hand is that's checking it! By knowing the temperature they can use that same temperature in any other similar test and compare the results more accurately. Simples!
---- OR ----

Sign up for a £1 trial so you can track and measure your child's progress on this activity.

What is EdPlace?

We're your National Curriculum aligned online education content provider helping each child succeed in English, maths and science from year 1 to GCSE. With an EdPlace account you’ll be able to track and measure progress, helping each child achieve their best. We build confidence and attainment by personalising each child’s learning at a level that suits them.

Get started
laptop

Start your £1 trial today.
Subscribe from £10/month.