Chemistry: pH scales and acidity

DiScoro writes about inquiry-based learning, digital resources, and ways to encourage higher-order thinking. We focus on STEM education and the use of technology.

The PHET simulation pH Scales enables students to experiment with acidic and basic fluids.

Note that pH scale and acidity are complex concepts for students especially for primary school pupils. A lower pH value means more ‘acidic’ and a higher value means less acidic, or more ‘basic’.  Neutral is indicated by the pH value 7.0.

However, the simulation can help the students to familiarize themselves with the concept(s). The simulation can be used in grade 6 or 7. Depending on how much time you wish to spend and how much structure you wish to give, in addition to the simulation, you could encourage the students to experiment and discover the basics about pH values in fluids and its application in every day life.

Suggestions for tasks and experiments:

  1. Check out the different fluids available.
    Rank the fluids from most basic to most acidic before you start measuring. Write down your estimation.
  2. Measure the pH values for the fluids given and write the results in a table.
    Which fluids are closest to pH 7.0?
    What does it mean if  the pH value of a fluid is close to 7.0?
  3. Use water to dillute the fluids and try to make a fluid that is closest to 7.0.
    Write down what you have done to reach your result.
    Make a screencast of your closest result(s) and print it out.
  4. Can you dillute a basic fluid with water to a pH value below 7.0?
    Can you dillute an acid fluid with water to a pH value above 7.0?
    Try to explain the result?

Think beyond the simulation.

  1. How could you make an acidic fluid basic? In other words, how could you for example change the pH value of an acidic fluid from 5.0 to 7.5?
  2. a. Your body functions best if the pH value is neutral. How does your body manage this?
    b. With the knowledge about the pH value of your body, how can you support your body to remain healthy?

pH value paper strips

In addition to the simulation students could use pH paper strips to measure the acidity of fluids. It becomes particularly interesting if the fluids you use can be tasted. Students can describe the taste they experience. Use for example coca cola or other fizzy drinks, fruit juice, tea, milk, coffee, water. This real life experiment makes it possible to neutralise an acid/basic fluid using other chemicals, for example by adding bicarbonate (baking soda) to an acidic fluid.

battery hydrometer

Another interesting tool is a battery gravity hydrometer, which actually measures the acidity (pH value) of the battery acid. You could also say that it measures the gravity of the battery fluid. Together with a Volt meter it is used to check if the battery is charged and in good condition If your battery is fully charged the pH value should be near 1.28. If the battery is discharged, the pH value will be near 1.14. The battery hydrometer only measures accurate with pH values around 1.2. So is useless to measure pH values over 2.

More PHET simulations. See also Balancing Act, The moving man, Energy skate park, and Density and Buoyancy.

 Purchase  Free
 Hardware  PC, iPad
 Requirements  browser
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