Salty crisps

Kin Yu’s mum has high blood pressure. Her doctor has told her to cut down on the amount of salt she eats.

This experiment should take 120 minutes. 

Equipment

• Eye protection
• Filter funnels
• Filter papers
• Glass beakers
• Wash bottles
• Glass stirring rods
• Evaporating dishes
• Bunsen burners
• Tripods
• Gauzes
• Heat-resistant mats
• Clamp stands
• Access to balances
• Writing and/or display materials (sugar paper, felt tip pens etc) are also required
• Binocular microscope x 50 magnification
• Access to water
• Per group 1 packet of each of 3 different brands of ready salted crisps

Health, safety and technical notes

• Read our standard health and safety guidance here.
• Always wear eye protection. 
• This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.
• The taste test should be conducted outside the laboratory and not after any contact with chemical solutions. 
• It is the responsibility of the teacher to carry out a suitable risk assessment.

Possible approaches

7–11-year-olds will probably go for a taste test.

Questions to ask students who need further help:

1. How can they make it fair?
2. Does it matter if your mouth is already salty?
3. Does it matter if the crisps are different sizes?
4. Does it have to be a taste test?
5. Could they wash the salt off and compare it?

(One unexpected method adopted by a number of students in the 7–11 age range was to ask for a binocular microscope (× 50 magnification) and count the salt grains!)

11-16 year old students tended to wash the salt off the crisps with cold water (messy! Other things dissolve as well) and collected the dissolved salt.

Students could then evaporate the salt solution to dryness and weigh the salt residue, or use a hydrometer to measure how salty the water is.

Alternatively, conductivity may be used. 

Possible extension 

Students could find out what other foods should not be eaten if you have ‘high’ blood pressure. Students could also test for the presence of starch in crisps. Comparison of salted peanuts.