Core practical - Analysis and purification of water (AQA GCSE Chemistry): Revision Notes
Core practical - Analysis and purification of water
What is this practical about?
This practical shows you how to get pure water from salt water using a process called distillation. You can also test water samples to check their pH and find out what ions are present in the water.
Aim of the practical
The goal is to obtain pure water from a solution that contains salt dissolved in water.
Equipment you need
Understanding your equipment is crucial for successful distillation. You'll need several key pieces of apparatus to complete this practical safely and effectively.
Essential Equipment List:
- Eye protection - always wear safety goggles
- Distillation apparatus - special equipment for separating liquids
- Bunsen burner - for heating
- Salt water - your starting mixture
- Anti-bumping granules - special stones that prevent dangerous bubbling
You should know the names of all the parts in the distillation equipment, including the flask and the condenser.
The method - step by step
The distillation process follows a specific sequence of steps that must be carried out carefully to ensure safe and effective separation.
Worked Example: Distillation Procedure
Step 1: Pour the salt water into the round-bottomed flask.
Step 2: Add anti-bumping granules to the flask. These stop the mixture from bubbling too violently.
Step 3: Set up the apparatus and turn on cold water to flow through the Liebig condenser.
Step 4: Heat the mixture gently with the Bunsen burner.
Step 5: Collect the pure water that drips out into your beaker.
How distillation works
The science behind distillation involves understanding the different boiling points of substances and how phase changes occur during heating and cooling.
The Science Behind Distillation:
- When you heat the salt water, only the water boils - the salt stays behind
- The water turns into water vapour (steam) and travels through the apparatus
- The cold water flowing through the condenser cools down the steam
- The steam condenses back into liquid water - but now it's pure!
- The salt is left behind in the original flask
Testing your results
You can test if your water is truly pure by checking for chloride ions. Salt is sodium chloride (NaCl), so if there are no chloride ions present, you know the salt has been removed successfully.
Why each step matters
Each component and step in the distillation process serves a specific scientific purpose that contributes to the overall success and safety of the procedure.
Purpose of Each Step:
- Anti-bumping granules ensure smooth boiling and stop the apparatus from rattling
- Gentle heating prevents the mixture from boiling too violently
- Cold water in the condenser is essential - it makes the water vapour turn back into liquid
- Proper setup ensures the pure water collects in the right place
Remember!
Key Points to Remember:
- Distillation separates pure water from salt water - water evaporates but salt doesn't
- Anti-bumping granules prevent dangerous violent boiling
- Cold water flowing through the condenser turns steam back into liquid water
- You can test the purity by checking for chloride ions
- Always wear eye protection during practical work