Acids and Bases Acids and bases We cant

Acids and Bases

Acids and bases: We can’t live without them • Taste can be one property that differentiates acids and bases. • In the case of acids, when you bite into a lemon or taste a salad dressing, you notice that it can be sour or tart. • In the case of bases or alkaline, when a dentist gives you a shot of a topical anaesthetic to numb that pain, you notice that it can be bitter. Baking powder or baking soda are other examples.

• Your own body secretes acids to digest food and extract nutrients. • The stomach secretes hydrochloric acid (HCl). • Now, What’s stopping the stomach from destroying itself? • Well, the stomach protects itself from the acids by its thick lining. • When food exits the stomach, the pancreas secretes bicarbonates (bases) that are mixed with the digested food. • The bicarbonates neutralize (diminish) the effects of the acid in the food as it moves down the intestine.

• Health problems: • Sometimes a person may experience a heartburn after eating too much food or food that is hard to digest. • A heartburn is felt when there is an excess of acid in the stomach by acid reflux in the oesophagus (Food tube) where the acid may sometimes climb up into the oesophagus.

GIRD: Gastro-intestinal Reflux Disorder: disorder where food is ejected back into the oesophagus due to over-eating.

• Other examples of acids: • Bees, wasps and some ants produce a venom that is acidic. • It causes a burning sensation when in contact with skin. • To neutralize the burning, you can apply baking soda and water.

• Other examples of bases: • Some plants like poison ivy produce a basic substance as a defence mechanism. When in contact with the ivy, the water in your skin mixes with the poison and a sever irritation can occur. To neutralize it, you can use vinegar or lemon juice.

p. H Scale • Acids and bases are very useful. But it is important to know their degree of acidity and alkalinity because they can be dangerous. • The p. H scale was created to measure the degrees of acidity and alkalinity of a substance. • Now, for example: rain water has a p. H of 5. 6 which is considered mildly acidic. But as the rain falls it mixes with pollutants in the air and its acidity increases. It can also increase the acidity of the soil and of water in lakes which can be dangerous for plants and animals. • TASTING IS DANGEOURS. It is not recommended to taste a substance to check its acidity and alkalinity.

• It is always important to read labels to know what you are dealing with.

Indicator • An indicator can be used to measure the acidity or alkalinity of a substance. It changes colour in the presence of either of these substance. • An indicator can be synthetic or natural. • Examples of natural indicators: Flowers, lichens, red-cabbage juice, tea and grape juice.

• Hydrangea blossoms are blue when the plant is cultivated in acidic soil and pink when it is cultivated in neutral or basic soil.

Other types of indicators • A litmus paper is another measure of acidity and alkalinity, but it does not indicate the degree (Strength) of the solution. They can be blue or pink.

• The following is a table showing you how litmus paper is used to detect acids and bases.

p. H: An accurate measurement scale • Now, we know that with the litmus paper is not precise enough. • Egg fish example from text book p. 186. • So we use something a bit more precise and that is the p. H paper or a universal p. H. It is based on 14 degrees. Each degree corresponds to a different colour. • So: • Acidic substances have a p. H below 7. • Basic substances have a p. H above 7. • Substances with a p. H of 7 are neither acidic nor basic. They are neutral.

For acidity, you multiply by ten when you decrease by one unit. (x 10) For alkalinity, you divide by ten when you increase by one unit. (x 10)

SO, on the p. H scale, a jump of one corresponds to a power of ten. 1 2 3 x 10 4 x 10 5 6 7 8 9 10 11 12 13 A solution having a p. H of 3 is ten times more acidic than a p. H of 4. Whereas a solution having a p. H of 2 is one hundred times more acidic than a p. H of 4. x 102 14

p. H meter • The p. H meter is an electric device. • Fact: Acids and bases conduct electricity. • The meter measures the p. H of substances by using their capacity to conduct electricity. • The more acidic or basic the substance, the better it conducts electricity.