What’s your pH? – Acids and Bases


Creative Commons Image from Britt Gow

Learning Intention: To develop an understanding of acids and bases and the chemical reactions they are part of.

Success Criteria: You will be able to describe the differences between acids and bases and give several household examples of how they are used. You will perform some simple chemical reactions and identify that the  colour changes indicate the pH of the mixture.

Today we will be doing an experiment with acids and bases – making a pH indicator using red cabbage and testing various household substances. PH is a measure of the acidity (ph is less than 7) or alkalinity (ph is greater than 7) of a substance.

Another experiment we will do this week demonstrates how antacids work in your stomach. We will add dilute hydrochloric acid to a conical flask, which simulates the gastric juices in your digestive system. We will then add universal indicator to show the level of acidity. We will then add an antacid (alka-seltza tablet) and show how the pH increases, which demonstrates that the solution has become less acidic. When an acid and a base are mixed together the chemical reaction that takes place is called a neutralisation. The acid and base react to form a salt and water.

When metals are placed in acid they can corrode. An acid and a metal react together to produce hydrogen gas and a salt. You can test for hydrogen gas using the ‘pop’ test – light a match at the mouth of the test tube and you will hear a ‘pop’. Acid rain is problem in the northern hemisphere, caused by air pollution. We will learn more about acid rain in class.