The purpose of this laboratory is three fold:
1. Familiarize the student with the concept and meaning of pH
2. Provide the student experience in measuring pH
a. pH testing paper
3. Test the student’s hypothesis as it related to the pH of common solutions
Hypothesis
The pH of the tested solutions will be in the order of the following according to a pH scale:
1. Lime juice
2. Orange juice
3. Soda
4. Iced Tea
5. Milk
6. Water
7. Soapy water
Material Required
To facilitate this laboratory exercise, the experimenter needs the following: pH strips
Sample reservoirs of solutions with varying pH
Laboratory Notebook pH paper
Background pH stands for potential hydrogen. This is a measure of the acidity or basicity of a solution. Acidic and basic are two extremes that describe a chemical property chemicals. Mixing acids and bases can cancel out or neutralize their extreme effects. The pH scale is a set of standard solutions whose pH is established by international agreement. A substance that is neither acidic nor basic is neutral. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline. Pure water has a pH very close to 7. The pH scale is logarithmic and as a result, each whole pH value below 7 is ten times more acidic than the next higher value. For example, pH 4 is ten times more acidic than pH 5 and 100 times (10 times 10) more acidic than pH 6. The same holds true for pH values above 7, each of which is ten times more alkaline than the next lower whole value. For example, pH 10 is ten times more alkaline than pH 9 and 100 times (10 times 10) more alkaline than pH 8. Primary pH standard values are determined using a concentration cell with transference. This measures the potential difference between a hydrogen electrode and a standard electrode. Measurement of pH for solutions can be done with a glass electrode and a pH