This video creates an amazing colour-changing liquid you can make with cabbage. The solution shows if a substance is an acid or base. When the cabbage solution is mixed with another liquid, a colour change occurs and indicates if the solution is acidic or basic. This is a fun, visual experiment that uses everyday objects.
Some very common household solutions are acids and bases. Acids are solutions that will donate hydrogen ions in a solution, and usually taste sour. Some common acids are citrus fruit juices and household vinegar. Bases are solutions that accept hydrogen ions in solution, and usually feel slippery. How do you tell if something is an acid or a base? You use a chemical called an indicator, which changes in colour depending on whether a solution is acidic or basic (alkali). (Specifically, an indicator works by responding to the levels of hydrogen ions in a solution.) There are many different types of indicators, some are liquids and some are concentrated on little strips of “litmus” paper. Indicators can be extracted from many different sources, including the pigment of many plants. Red cabbage contains an indicator pigment molecule called flavin. Very acidic solutions will turn anthocyanin, a red colour. Neutral solutions result in a purplish colour. Basic solutions make a greenish-yellow or yellow colour. Because red cabbage has this indicator pigment, it is possible to determine the pH of a solution based on the colour it turns the red cabbage juice. The pH of a solution is a numerical measure Chemistry Kitchen of how basic or acidic it is. A solution with a pH between 5 and 7 is neutral, 8 or higher is a base, and 4 or lower is an acid (see figure 1).
This video experiment has four worksheets. The first is a results worksheet that students can fill out in class. The remaining three are the early, middle and upper year worksheets. Access to worksheets and extension activities are available in the teacher resource pack to Kitchen Chemistry.
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