Difficulty of Project
It is recommended that you do not lick the pH paper. See below for additional details.
Materials are readily available, except for the pH paper, which can be purchased online or at a well-stocked local pharmacy. Search for “pH Test Strips” or “pH paper”. Choose paper such as colorpHast* pH Test Strips, EMD Chemicals, which can test the entire acid/base range, from 0 to 14. This is available from online stores such as http://vwrlabshop.com.
Approximate Time Required to Complete the Project
5 hours of active time, plus time to acquire materials. (If you order the pH paper online, you will need to wait for it to arrive.)
Quench your thirst with great tasting lemonade while you explore the concepts of acid and base, and how these differ from sweet and sour.
Materials and Equipment / Ingredients
- Lemon Juice – bottled or fresh-squeezed, – at least 4 oz.
- Sugar – at least 4 oz.
- Baking soda – at least 4 oz.
- 4 oz. cups for lemon juice and sugar and baking soda
- 8 oz. cup
- Teaspoons – 5 or more
- Measuring spoon: tablespoon size
- Paper towels or cloth towels (for spills)
- Other items to test: Oranges or other juicy fruit, bottle of apple juice, club soda, liquid soap (all optional)
- Paper and pencil to make chart (or print out sample below)
- pH test paper. One roll or 25 strips.
The citric acid in lemons is what makes lemon juice taste sour. Scientists have another way of describing acidic things like lemon juice: they refer to the pH of an item. They have a special kind of paper they use to test how much acid is in a liquid: pH paper. The pH paper will turn different colors depending on how much acid is in the liquid.
Lemonade is a drink that transforms sour lemon juice into a sweet concoction, with the addition of sugar and water. When sugar is added to the lemon juice and makes it sweeter, does the liquid change from an acid to its opposite, a base?
In this science experiment, you’ll test the acidity of lemon juice by using pH paper, a special chemical paper. Then, as you add water and sugar to your lemon juice to make lemonade, you’ll measure the pH level again, and see how it changes.
- Is plain lemon juice an acid or base? What is its pH level?
- Is water an acid or base? What is its pH level?
- Is sugar water an acid or base? What is its pH level?
- Is lemonade an acid or base? What is its pH level?
- What is the pH level of your saliva?
- Does the lemon juice taste sweet or sour?
- Does the lemonade taste sweet or sour?
- Does the baking soda taste sweet or sour, or bitter?
- Do sweet and sour correspond to base and acid?
Terms, Concepts and Questions to Start Background Research
In this science experiment, you quench your thirst with great tasting lemonade while you explore the concepts of acid and base, and how these differ from sweet and sour. The degree of acidity of the lemon juice and lemonade is measured using pH paper.
- Acid: An acid refers to any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity higher than that of pure water, i.e. a pH lower than 7.0. Lemon juice and vinegar are common household acids. These taste sour.
- Base: No, we’re not talking about baseball bases. A base, when used in chemistry, refers to any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity lower than that of pure water, i.e. a pH higher than 7.0. Baking soda, soap, ammonia and chalk are all bases. Edible bases, like baking soda, taste bitter.
- Sweet: One of the basic tastes; the taste of sugar.
- Sour: One of the basic tastes; the taste of lemon juice.
- pH: A measure of the acidity or alkalinity of a solution, numerically equal to 7 for neutral solutions, such as water, and increasing with increasing alkalinity and decreasing with increasing acidity. The pH scale commonly in use ranges from 0 to 14. pH is an abbreviation for "potential of hydrogen”. A pH of 7 is considered "neutral", because the concentration of hydrogen ions is exactly equal to the concentration of hydroxide (OH-) ions produced by dissociation of the water. Increasing the concentration of hydrogen ions produces a solution with a pH of less than 7, and the solution is considered "acidic". Decreasing the concentration produces a solution with a pH above 7, and the solution is considered "basic".
- pH Paper: This paper, which comes in strips or rolls, is sometimes called litmus paper. The paper is specially coated with one or more chemicals. The chemicals change different colors when they come into contact with a liquid base or acid. To tell the pH of the liquid, the resulting color is compared to a chart.