Separating Substances: the Seaside Worksheet

In this worksheet you're going to take a journey to the seaside with Amy and Sam to investigate seawater, what it's made of and how to separate its various constituents.

Seaside

So, let's see what Amy and Sam are up to.

Amy and her brother, Sam, were on a school trip to a nearby seashore.

Children with bucket of seawater

Amy filled her bucket with water from the sea and showed it to Sam: "That's got salt in it, Sam" she said. "Ugh, it's got bits of seaweed in it," Sam observed.

Bucket at seaside

Back at school Sam asked Amy, "How can we get the seaweed out?"

What do you think Amy and Sam should do to separate the seaweed and sand from their seawater?

filter it

evaporate it

condense it

Here are some pieces of apparatus they had in the classroom:

Flask
Microscope
Bunsen Burner
Funnel
Filter Paper
Thermometer

Select all of the equipment that they will need to separate the seaweed and sand from the seawater.

Flask

Microscope

Bunsen burner

Funnel

Filter paper

Thermometer

"There you are, Sam, that's cleaned the seawater," Amy told her brother.

"But how does it work?" asked Sam.

What do you think Amy told Sam to explain how their apparatus removed the bits of seaweed and sand from the seawater?

the bits were attracted to the filter paper

the bits were too big to fit through the holes in the paper

gravity held the bits in the filter paper

"Is it safe to drink now?" asked Sam. "Oh no," exclaimed Amy, "it's still full of salt!"

"How can we get the salt out then?" Sam wanted to know. "Oh that's easy!" laughed Amy.

Here's the apparatus Amy set up:

Evaporation apparatus

What happened when Amy heated the seawater gently?

Sam saw all the water boil away

Sam saw steam leaving the dish

Sam saw the water turn blue

After a few minutes they saw a ring of white crystals appearing above the seawater.

"Look," cried Sam, "is that salt?"

Salt crystals

Why was the salt left behind?

salt is a solid and cannot boil away

salt always sticks to the side of containers

salt separates from hot water

Sam looked mournfully at the salt. "I can't drink that!" he cried.

"Oh no, I've done the wrong experiment!" laughed Amy.

Sam wanted Amy to "get the salt out" of the seawater - why is her experiment wrong?

she shouldn't have heated the seawater

she shouldn't have let the water evaporate

she should have collected the water

"Never mind, there's lots of seawater left," chuckled Amy, "let's try again."

This time, when Amy heated the seawater gently, she used gloves to carefully hold a cold surface near the steam coming away from the hot seawater.

"Look Sam!" exclaimed Amy, "what do you see collecting on the surface?"

What do you think Sam saw?

salt

steam

water

"Is that stuff salty?" Sam wanted to know.

Do you think that there's any salt in the steam coming away from the hot seawater?

Yes because when salt dissolves in water it becomes a liquid and boils away when heated

No because salt is a crystal and crystals don't evaporate

No because salt remains as a solid in solution and cannot evaporate

The substance that Amy and Sam collected on the cold surface was cooled from the steam.

Water droplets

When steam cools and turns back into a liquid we say that the steam has....

evaporated

boiled

condensed

Looking at the substance that collected on the cold surface Sam asked Amy "Is it safe to drink now? Is it clean water?"

Do you think Amy should allow Sam to try some?

Yes, it's safe now

No, it's got salt in it

No, it might have microbes in it

ANSWERS

Question 1

Amy and her brother, Sam, were on a school trip to a nearby seashore.

Children with bucket of seawater

Amy filled her bucket with water from the sea and showed it to Sam: "That's got salt in it, Sam" she said. "Ugh, it's got bits of seaweed in it," Sam observed.

Bucket at seaside

Back at school Sam asked Amy, "How can we get the seaweed out?"

What do you think Amy and Sam should do to separate the seaweed and sand from their seawater?

CORRECT ANSWER

filter it

EDDIE SAYS

The solid particles of seaweed and sand are too big to fit through the tiny holes in the filter paper and so are trapped, allowing the seawater to pass through.

ANSWERS

Question 2

Here are some pieces of apparatus they had in the classroom:

Flask
Microscope
Bunsen Burner
Funnel
Filter Paper
Thermometer

Select all of the equipment that they will need to separate the seaweed and sand from the seawater.

CORRECT ANSWER

Flask
Funnel
Filter paper

EDDIE SAYS

The FILTER PAPER is fitted into the FUNNEL and placed into the FLASK so that the seawater can be poured in allowing the cleaned seawater to drip into the flask.

ANSWERS

Question 3

"There you are, Sam, that's cleaned the seawater," Amy told her brother.

"But how does it work?" asked Sam.

What do you think Amy told Sam to explain how their apparatus removed the bits of seaweed and sand from the seawater?

CORRECT ANSWER

the bits were too big to fit through the holes in the paper

EDDIE SAYS

The tiny holes in the filter paper allow the seawater to pass through but the bits of seaweed and sand are too big and get trapped.

ANSWERS

Question 4

"Is it safe to drink now?" asked Sam. "Oh no," exclaimed Amy, "it's still full of salt!"

"How can we get the salt out then?" Sam wanted to know. "Oh that's easy!" laughed Amy.

Here's the apparatus Amy set up:

Evaporation apparatus

What happened when Amy heated the seawater gently?

CORRECT ANSWER

Sam saw steam leaving the dish

EDDIE SAYS

When Amy started to heat the seawater gently it became hotter and began to steam. It would only boil away if Amy heated it until all the water was gone, which is a bad idea.

ANSWERS

Question 5

After a few minutes they saw a ring of white crystals appearing above the seawater.

"Look," cried Sam, "is that salt?"

Salt crystals

Why was the salt left behind?

CORRECT ANSWER

salt is a solid and cannot boil away

EDDIE SAYS

When a solid, like salt or sugar, dissolves in water it spreads out into tiny, tiny particles but IT IS STILL A SOLID. That means when all the water evaporates away, the salt stays behind. If you find that hard to understand consider a pool with fish in. In hot weather water evaporates, the level goes down and the fish have less and less water to swim in - they cannot evaporate away!

ANSWERS

Question 6

Sam looked mournfully at the salt. "I can't drink that!" he cried.

"Oh no, I've done the wrong experiment!" laughed Amy.

Sam wanted Amy to "get the salt out" of the seawater - why is her experiment wrong?

CORRECT ANSWER

she should have collected the water

EDDIE SAYS

When Sam wanted Amy to "get the salt out" of the seawater that's because he wanted to have clean, unsalty water to drink. When Amy heated the seawater she allowed all the water to evaporate away when, in fact, she really wanted to collect it!

ANSWERS

Question 7

"Never mind, there's lots of seawater left," chuckled Amy, "let's try again."

This time, when Amy heated the seawater gently, she used gloves to carefully hold a cold surface near the steam coming away from the hot seawater.

"Look Sam!" exclaimed Amy, "what do you see collecting on the surface?"

What do you think Sam saw?

CORRECT ANSWER

water

EDDIE SAYS

Sam would have seen steam, but when it touched the cold surface it would have CONDENSED (cooled down) into droplets of water which would have collected on the surface and then started to dribble to the bottom.

ANSWERS

Question 8

"Is that stuff salty?" Sam wanted to know.

Do you think that there's any salt in the steam coming away from the hot seawater?

CORRECT ANSWER

No because salt remains as a solid in solution and cannot evaporate

EDDIE SAYS

If you decided that crystals don't evaporate you're nearly right - in fact a very few, like iodine crystals do evaporate, but that's another story! Here the salt cannot evaporate because although it's in the seawater it's STILL A SOLID. Remember the fish in the pond that's drying up - if all the water goes can the fish evaporate? Same thing really!

ANSWERS

Question 9

The substance that Amy and Sam collected on the cold surface was cooled from the steam.

Water droplets

When steam cools and turns back into a liquid we say that the steam has....

CORRECT ANSWER

condensed

EDDIE SAYS

When a liquid is heated (it gets lots more energy) it evaporates into a gas. BUT when a gas (like steam) is COOLED down (losing energy) it turns back into a liquid. That means it CONDENSES (and forms condensation!). So evaporation is when things are getting hotter and condensing is when they're getting cooler.

ANSWERS

Question 10

Looking at the substance that collected on the cold surface Sam asked Amy "Is it safe to drink now? Is it clean water?"

Do you think Amy should allow Sam to try some?

CORRECT ANSWER

Yes, it's safe now

EDDIE SAYS

To be honest it's probably perfectly all right: as long as Amy used clean apparatus and, especially, made sure that the surface she condensed the steam on to was clean it should be safe to drink. There can't be any salt in it (that's still in the dish) and any microbes in the seawater would be killed and couldn't evaporate anyway!

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