Acids, Bases and Indicators

What are Acids? Common substances used in everyday life Some occur naturally & some are synthetic Some are dangerous because they are corrosive (they can ‘eat away’ metal, wood and clothing and burn your skin). Acids can be dilute (contains a large amount of water) or concentrated (must be handled with great care).

What are Acids? Strong Acids Weak Acids Sulfuric Acid (H2SO4) Citric Acid (citrus fruit and tomatoes) Hydrochloric Acid (HCl)- In your stomach to aid digestion Lactic Acid (yoghurt) Nitric Acid (HNO3) Acetic Acid (vinegar) Tartaric Acid (grapes) Carbonic Acid (Soft drink) Deoxyribonucleic Acid (DNA)

What are Bases? Bases neutralise (cancel out) acids E.g. toothpastes contain weak bases to neutralise acid on your teeth Used to dissolved grease or dirt Bases that are soluble in water are called alkalis They feel soapy because they turn the oils on your skin into soap

Acids and Teeth When you eat, food remains between your teeth Bacteria in your mouth feed on this food Bacteria produce weak acids as waste These acids react with your teeth causing decay The mixture of bits of food, bacteria, acids and saliva that stick to your teeth is called plaque

Acids and teeth The top of the tooth is covered in enamel (hardest substance in the body) The inside of the tooth is made of a softer substance called dentine If the bacteria & acids cause the enamel to decay, the tooth can be damaged rapidly

Acids and Teeth The best way of getting rid of plaque and food particles from your teeth is by brushing them Toothpastes contain abrasives such as finely powdered chalk that help scrape food particles from your teeth Some toothpastes are highly basic to neutralise acids of decaying food These react with tooth enamel in young people’s teeth to form a substance that is more resistant to acid attack

Stomach Acid Gastric juice is produced in your stomach to help to digest the food you eat This gastric juice consists of dilute hydrochloric acid, enzymes and water The hydrochloric acid helps to kill most microbes It also helps the enzymes to work as they will only function in the presence of an acid Enzymes break down the proteins in your food into amino acids which are needed for growth You stomach is protected from the acid by a sticky fluid called mucus

Acids in Food and Drink Baking powder and self-raising flour contain baking soda (sodium hydrogen carbonate) and an acid substance such a scream of tartar When it becomes moist the baking soda reacts with the acid to form carbon dioxide gas The gas is trapped in the mixture in the form of bubbles and causes the cake to rise in the oven Acids are also used to preserve food by preventing bacteria growth, e.g. vinegar in pickles or sauces

Indicators A quick way to tell if a solution is acidic, basic or neutral is to use an acid-base indicator Indicators indicate when an acid or base is present by changing colour Some indicators occur naturally in dyes in plants E.g. litmus comes from lichens which grow on the bark of trees & on rocks In an acidic solution litmus turns red; and in a basic solution, it turns blue.

Indicators There are also a number of synthetic indicators http://www.bbc.co.uk/bitesize/ks3/science/chemical_material_behaviour/acids_bases_metals/activity/