CHEM1201 Lecture Notes - Lecture 17: Burette, Erlenmeyer Flask, Equivalence Point
7 Jun 2018
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Revision:
• H+ in water solution exists as H3O+
• An acid can donate an H+
• A base can accept an H+ (or increase concentration of OH )
• Compounds can be identified as acids or bases by their structures
• Acids and bases can be strong or weak
– fully or partly ionised (<10%)
• Products of acid‐base reactions can be predicted.
• Balanced chemical equations can be written to describe acid‐base reactions
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Useful acid-base reactions:
- Reducing stomach acidity
o Stomach produces HCl (normal pH = 2)
o Under stress may produce too much (pH = 1)
o Excess acid leads to ulcers
o Temporary relief = taking antacids
o E.g. milk of magnesia (Mg(OH)2)
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o e.g. Alka-seltzer (NaHCO3)
▪
- Overcoming the effects of acid rain
o Normal rainwater is slightly acidic (pH = 5.6) due to weak solution of carbonic
acid (H2CO3)
o Acid rain (pH = 4.0)
▪ SO2 and nitrogen oxides released by coal fired power stations are
converted to droplets of nitric and sulfuric acid
o Where soils contain limestone (CaCO3) and dolomite (CaMg(CO3)2)
▪ Acid rain is neutralised naturally before it enters the water table
▪
o Where soils are more acidic
▪ Can cause acid to build up in lakes, rivers, soils, etc.
▪ Lime (Ca(OH)2) can be added to neutralise the acidic build up
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o the interaction of acids from acid rain with carbonates and metals can
damage building materials e.g. limestone, marble, cement, metals, etc.
- Baking cakes
o Why do many baked goods (e.g. cakes) rise?
▪ Interaction of bicarb soda (NaHCO3) with a weak acid (e.g. lactic acid
in milk) in a moist, warm environment
▪
▪ bubbles of CO2 gas form when the dough is heated in the oven
causing the dough to rise
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Document Summary
Fully or partly ionised (<10%: products of acid base reactions can be predicted, balanced chemical equations can be written to describe acid base reactions. Reducing stomach acidity: stomach produces hcl (normal ph = 2, under stress may produce too much (ph = 1, excess acid leads to ulcers, temporary relief = taking antacids, e. g. milk of magnesia (mg(oh)2, e. g. alka-seltzer (nahco3) Interaction of bicarb soda (nahco3) with a weak acid (e. g. lactic acid in milk) in a moist, warm environment: bubbles of co2 gas form when the dough is heated in the oven causing the dough to rise. Acidity of a solution depends on: the type of acid used (weak or strong, the amount of acid used (concentrated or dilute) Ph scale: scale used to quantify acidity (or basicity, as acids produce h3o+ in solution, measuring the amount of h3o+ allows a relative measurement of the acidity of the solution. A neutral solution contains equal amounts of acid and base.
