Acids and alkalis in foods

UNDERSTANDING YOUR FOOD<br /> the ultimate educational resource<br /> TEACHER NOTES<br /> <br /> teachers’ notes A3.1<br /> A3. Acids and alkalis in food<br /> Pupils make sherbet and look at food labels for presence of acids. (Some<br /> of theinformation on the pupil activity sheet repeats the work done on A1, a<br /> science activity)<br /> Making sherbet<br /> Hints for the teacher<br /> • Use citric acid and sodium hydrogencarbonate (bicarbonate of soda)<br /> suitable for consumption (citric acid suitable for eating can easily be<br /> obtained from a pharmacist).<br /> • Pupils may like to have lollipops/liquorice if some of the sherbet is<br /> to be eaten straight away.<br /> •It may be desirable to sieve the ingredients together to ensure thorough<br /> mixing.<br /> A simple experiment, such as mixing each substance alone with water and<br /> then combinations of the substances with water, will show that the icing<br /> sugar is not essential to the fizzing reaction whereas the other two<br /> ingredients are. The sherbet must be kept in a sealed container until<br /> consumed so that it does not react with moisture in the air.<br /> Find the acid<br /> Answers to questions on Pupil activity sheet A3<br /> 2. The results will depend on the labels which are used.<br /> 3. To impart a characteristic, tart taste (e.g. citric acid for lemons; malic<br /> acid for apples).<br /> Do we drink acids?<br /> SeeHow much acid is present in fizzy drinks?<br /> Activity A1.<br /> KS3/4<br /> food technology<br /> Timing – 30 minutes.<br /> Pupil activity sheet A3 accompanies<br /> this activity.<br /> Requirements per group<br /> 9 teaspoons of icing sugar<br /> 2 teaspoons of citric acid<br /> 1 teaspoon of sodium<br /> hydrogencarbonate<br /> <br /> pupil activity A3 ACIDS AND ALKALIS IN FOODS<br /> The reactions between acids and alkalis are very important in everyday life as well as<br /> in both food technology and science lessons.<br /> Making sherbet<br /> Sherbet fizzes when it comes into contact with moisture on your tongue. Sherbet can<br /> be made from icing sugar, citric acid and sodium hydrogencarbonate (an alkali; it is<br /> sometimes called sodium bicarbonate or bicarbonate of soda).<br /> Can each of these chemicals make the fizz on their own? Or is a combination of 2 or<br /> all 3 of them needed? Plan a simple experiment to find out.<br /> You can then make your own sherbet by using the following recipe:<br /> 9 teaspoons of icing sugar<br /> 2 teaspoons of citric acid<br /> 1 teaspoon of sodium hydrogencarbonate<br /> Mix all the ingredients very thoroughly. Keep the sherbet in a sealed container until you<br /> want to eat it. Why do you think this is important?<br /> Find the acid<br /> 1.Find the labels from at least 10 items of food and drink that containacids.<br /> 2.Make a table into which you can put thenameof the food or drink and the<br /> acid it contains.<br /> 3.Why do food manufacturers add acids to foods?<br /> Do we drink acids?<br /> The use of artificial sweeteners in soft drinks has helped to reduce the amount ofsugar<br /> we eat. This has also reduced the amount of tooth decay. Tooth decay is caused by<br /> the production ofacidsbybacteriainplaque. Tooth decay should not be confused<br /> withtooth erosion. The acids found in many of the foods and drinks we consume can<br /> cause the loss of tooth enamel. This is known aserosion.<br /> The frequent exposure of teeth to anyacidic food or drink may cause this chemical<br /> erosion.<br /> Use Universal indicator to find out the pH of a range of drinks. Make sure you test tap<br /> water, cola, fizzy lemonade, blackcurrant juice, orange squash, milk and freshly<br /> squeezed orange or lemon juice.<br /> Present your results in a suitable way.<br /> If your teeth are in contact with acidic foods, not just fizzy drinks, tooth erosion may<br /> occur. Think of any advice you could give to individuals who like to drink acidic drinks<br /> so that the effects of the acid are as reduced as is possible.