acids

• an acid is a proton donor
• an acid is a substance which produces hydrogen ions when dissolved in water
• acids taste sour
• strong acids are corrosive
• weak acids are irritant
• acid turns moist blue litmus paper red
• acids have a pH less than 7
• acids can conduct electricity
• hydrochloric acid- HCl

  source- stomach
• sulphuric acid -H2SO4

  source- car battery
• nitric acid- HNO3

  source- fertilizers and explosives
• ethanoic acid- CH3COOH

  source- vinegar
• a chemical formula indicates the name and exact number of each atom present
• citric acid- C6H8O7

  source- citrus fruits
• ascorbic acid- C6H8O6

  source- fruits and vegetables
• methanoic acid- HCOOH

  source- ant venom
• carbonic acid- H2CO3

  source- fizzy drinks
• acid + alkali = salt + water

  hydrochloric acid + sodium hydroxide = sodium chloride + water

  HCl (aq) + NaOH(aq) = NaCl (aq) = H2O(l)
• acid + reactive metal = salt + hydrogen gas

  hydrochloric acid + potassium = potassium chloride + hydrogen

  2HCl(aq) + 2K(s) = 2KCl(aq) + H2(g)
• acid + carbonate = salt + carbon dioxide + water

  
  

  hydrochloric acid + sodium carbonate = sodium chloride + carbon dioxide + water

  
  

  2HCl(aq) + Na2CO3(aq) = 2NaCl (aq) + CO2(aq) + H2O(aq)
• strong acids are completely ionised or dissociated into hydrogen ions when dissolved in water
• weak acids are partially ionised or dissociated into hydrogen ions when dissolved in water
• the lower the pH the stronger the acid

  the higher the pH the weaker the acid
• methanoic acid found in ants bite also known as formic acid

  treatment- (neutralise the acidic sting with a weak alkali)

  • toothpaste
  • baking soda
  • calamine lotion
• baking soda contains Sodium hydrogencarbonate

  acid + hydrogencarbonate = salt + water + carbon dioxide

  H+(aq) + HCO-3(aq) = H2O(l) + CO2(g)
• citric acid found in fruits

  • if lime juice is added to rust stains a neutralisation reaction occurs between the acid and base
• effect of heat on ascorbic acid/ vit c-

  • heating decreases the vit c content by a process called oxidation which destroys the vit c in fruits and vegetables. adding sodium hydrogencarbonate to ascorbic acid-
  • improves texture and appearance, the vit c is neutralised therefore reducing the vit c content
• use of vinegar in food preservation-

  • its low pH denatures enzymes which cause decay and prevents growth of fungi and bacteria
• lactic acid found in milk and tired muscles-

  • lactic acid is produced during anaerobic respiration
• USE: Toothpaste

  ACTIVE INGREDIENTS: Sodium hydrogen carbonate (NaHCO3) and sodium monofluorophosphate (Na2FPO3)

  EXPLANATION:

  • Toothpaste helps reduce tooth decay which is caused by acid in the mouth by reacting with the calcium hydroxyapatite (Ca10 (PO4)6 (OH)2 in tooth enamel.

  • Sodium hydrogen carbonate neutralises any acid present.

  • Calcium fluoroapatite does not react with the acid, therefore tooth enamel

  is protected from decaying.
• USE: Soil treatment

  ACTIVE INGREDIENTS: ‘Lime’ in the form of calcium oxide (CaO) or

  calcium hydroxide Ca(OH)2

  EXPLANATION:

  •Adding lime to soil neutralises any acids present, since most plants grow best if the soil is neutral.

  •Too high a pH severely restricts plant growth and may cause yellowing in plants.

  •Soils left untreated eventually become acidic. Acids are continually being added to the soil in rain water which has dissolved oxides of sulphur and nitrogen from the air (acid rain).
• Lime cannot be added at the same time to as an ammonium fertilizer because the two react to form a salt, ammonia and water. Lime causes the nitrogen to be lost by the reaction with the ammonium salts.
• To increase the pH of the soil things can be added such as :

  slaked lime, Ca(OH)2

  ground limestone, CaCo3

  quicklime, CaO
• USE: Antacids

  ACTIVE INGREDIENTS: Sodium hydrogen carbonate (NaHCO3), Magnesium hydroxide, Mg (OH)2, aluminium hydroxide, Al (OH)3 or magnesium carbonate, MgCO3

  EXPLANATION:

  • Antacids are used to treat indigestion and acid reflux. They do this by

  neutralising excess hydrochloric acid in the stomach.
• USE: Baking Soda

  ACTIVE INGREDIENTS: NaHCO3, weak acid

  EXPLANATION: when water is added to baking powder, a gas called carbon dioxide is evolved which make the product rise.
• USE: Fire extinguisher

  INGREDIENTS: NaHCO3 and KNCO3 (potassium hydrogencarbonate)

  some contain carbon dioxide