acids and alkalis

• Acids and alkalis are common in daily life. They are found in the home, in our bodies, in industry, car batteries and school science labs.
• One of the jobs of a chemist is to tell the difference between an acid and an alkali and know how they react with each other and with chemicals.
• Dilute acids


  Strong acids such as hydrochloric acid, sulfuric acid and nitric acid are laboratory acids that have been mixed with a lot of water before putting them out for use.
• Concentrated acids


  Acids mixed with very little water. They are much more dangerous than dilute acids.
• Concentrated acids are corrosive. They can attack metals and destroy skin if spilled.
• Weak acids


  Acids with a sour taste, like vinegar and lemon juice, which are safe to use in food.
• Base


  A substance that can react with an acid and neutralise it.
• Alkali


  A base that dissolves in water.
• Alkalis feel soapy when they get on your skin, so it is easy to tell when you have had an accident and must wash your hands.
• Concentrated alkalis are just as dangerous as concentrated acids, sometimes more dangerous, but many people do not realise this.
• Alkalis used in household cleaners


  • Sodium hydroxide
  • Ammonia
• Weak bases and alkalis found in


  • Toothpaste
  • Indigestion tablets
  • Baking powder
• Spilt dilute acids or alkalis should be immediately wiped up using a wet paper towel. The acid or alkali becomes more diluted, and so becomes less dangerous.
• Wear protective gear (goggles, long-sleeved clothes, and gloves) when using acids and alkalis
• Limit the volume of acids and alkalis used in the lab
• Cap the bottles of acid and alkalis tightly
• Litmus indicator


  Turns red in acidic solutions and blue in alkaline solutions. Turns purple in neutral solutions.
• Universal indicator


  Can show how strongly acidic or alkaline a solution is, using the pH scale from 0 to 14.
• Neutral solutions have a pH of 7, acids have a pH less than 7, and alkalis have a pH greater than 7.
• Neutralisation


  The reaction when an alkali is added to an acid, or an acid is added to an alkali, forming a neutral solution.
• Heat energy is released in the neutralisation reaction, so the reaction mixture warms up.
• Everyday examples of neutralisation


  • Farmers use lime to neutralise acid soils
  • Indigestion tablets contain alkalis to neutralise stomach acid
  • Baking powder neutralises acidic bee stings
  • Vinegar neutralises alkaline wasp stings
• Healthy saliva is usually slightly acidic, in the range pH 5.6 to 6.9. If saliva is too acidic the risk of tooth decay and cavities increases. If saliva is too alkaline it can cause enamel erosion of the teeth.
• The best way to reduce the effects of acidic foods and drinks is to drink water during and after eating, which dilutes the acid.
• Magnesium hydroxide


  Used to neutralise extra acid
• Magnesium carbonate


  Used to neutralise extra acid
• Baking powder


  Contains sodium hydrogen carbonate, used to neutralise bee stings
• Vinegar


  Contains ethanoic acid, used to neutralise wasp stings
• Farmers use lime (shown in white) to fertilise acidic soil
• Healthy saliva


  Slightly acidic - pH 5.6 to 6.9
• Saliva too acidic


  Increases risk of tooth decay and cavities
• Saliva too alkaline


  Causes enamel erosion of the teeth
• Sugary foods


  Tend to have a high acid content
• Acidic foods/drinks


  Fruits, tomatoes, coffee, fizzy drinks
• Drinking water


  Dilutes the acid from acidic foods/drinks
• Toothpaste


  Alkaline, helps neutralise acid
• Alkaline foods


  Rice, sweet corn
• Cheese


  Helps rebalance pH levels at the end of a meal
• Neutralisation reaction


  1. Acid added to alkali

  2. Indicator used to detect neutralisation point

  3. Acid and alkali reactants, salt and water products
• Salt


  Any compound formed by the neutralisation of an acid by a base or an alkali