Can you change the boiling point of water?

L/O :- To plan a test, follow lab safety rules when doing a practical, graph results and write a conclusion

Why do cooks put salt in the water when they cook

pasta?

I think the salt is added to the pasta to make it

taste better

If you add salt to the water the

water stays colder so the pasta cooks

slowly

Adding salt makes the water boil

faster

Adding the salt just makes them

look like they know what they are doing – they are showing off!!

I think the salt might increase

the boiling point so the water is

hotter

You are going to plan an experiment to test your ideas

Planning an investigation

Step 1 What are you investigating?

Step 3 Control variablesWhat variables do you need to keep

the same to make it a fair test?

Step 4Choosing the resolution

What scale of measurement are you going

to use?

Step 2 Independent

Variable What are you going

to change?Dependent

VariableWhat are you going

to measure?

Step 6 Do you need a control in your

experiment?

Step 5 What

equipment are you going

to need?

Step 7 What do you Predict will happen and

why?

Recording your Results

Design a table to collect your results in

1st 2nd 3rd

Independent

variable - the thing

you change

These are usually the things you have measured

NEVER FORGET YOUR UNITS!!! (e.g. (s), (m), (cm), (N)

Use a PENCIL and RULER

Conclusion – what do your results show?

Did adding salt to water affect the boiling point?

Are you results repeatable (did you repeat the test)?

Are you results reproducible - did other people do the same or similar test – did you compare results?

• Adding salt to water increase the boiling point

• In other words the water does not boil at 100C, but instead >100C (enough salt will cause it to boil at 105C)

• This is all because the salt dissolves in the water, changing the water’s properties - more energy is required to turn the solute (the salt) into its gaseous state

• So the more salt you add, the higher the boiling point will be (until you hit a limit, where no more salt can dissolve)!

What did you find out?Are your results

accurate?How do you know?

Was your resolution appropriate?

How do you know?

You can get more accurate results by removing anomalies when calculating a mean.

Did you use the smallest scale on your measuring instrument?