YEAR 12 CHEMISTRY
HSC MODULE 2: THE ACIDIC ENVIRONMENTIndicators were identified by observing that the colour of some flowers depends on soil composition.Classify common substances as acidic, basic or neutral.Strong acidic solution has a pH range of 1-3, whereby a weak acidic solution has a pH range of 4-6. However, a strong basic solution has a pH range of 12-14, and a weak basic solution of 8-11. A solution of pH 7 is considered neutral.
Carbonated soft drinks (e.g. coke)
Car battery acid
Washing soda solution
Baking soda solution
Identify that indicators such as litmus, phenolphthalein, methyl orange and bromothymol blue can be used to determine the acidic or basic nature of a material over a range, and that the range is identified by change in indicator colour.Chemists have developed a wide range of synthetic acid-base indicators. These indicators allow chemists to determine the range of acidity or basicity within very narrow limits.Identify and describe some everyday uses of indicators including the testing of soil acidity and basicity.Indicators are used for several things such as monitoring or finding the pH of swimming pools or testing the acidity of soil.Testing pH of swimming poolsPH of swimming pools should be near 7.4 so to avoid any health problems such as irritation in eyes of skin.Sodium hypochlorite (NaOCl) is added to kill microbes. This then reacts with water to form hypochlorous acid and hydroxide ions.OCl⁻ + H2O HOCl + OH⁻Hydroxide ions raise the basicity of the water, thus HCl is added to return water to normal pH.Phenol red is a suitable indicator in determining the correct acidity level of water.Testing pH of soilVarying plants grow best in either acidic or slightly alkaline soils.Soils that are too acidic can be partly neutralised by added bases such as crushed calcium carbonate.Whereas basic soils can be partly neutralised with fertilisers such as sulphate of ammonia or compost.A neutral white powder such as barium sulphate is sprinkled over the soil and drops of indicator are added, colour change is then observed. (The white powder allows colour change to be clearly seen).While we usually think of the air around us as neutral, the atmosphere naturally contains acidic oxides of carbon, nitrogen and sulphur. The concentrations of these acidic oxides have been increasing since the Industrial Revolution.Identify oxides of non-metals that act as acids and describe the conditions under which the act as acids.Oxides contain oxygen.ACIDIC OXIDESAcidic oxides dissolve in water to form acidic solutionsE.g. SO2 (g) + H2O (l) H2SO3 (aq) (sulfurous acid)Also, react with a base to form salt and water.E.g. SO3(g) + 2NaOH(aq) Na2SO4(aq) + H2O(l)Acid + Base Salt + waterBASIC OXIDESBasic oxides dissolve in water to form alkaline solutionsE.g....