Chemistry notes

Topics: Acid, PH, Hydrochloric acid Pages: 42 (13598 words) Published: May 16, 2014
9.3 – The Acidic Environment:
Δ. Construct word and balanced formulae equations of all chemical reactions as they are encountered in this module: NOTE: In chemistry, [x] means “concentration of x” in moles per litre (mol/L). EG: [H3O+] means “concentration of H3O+ ions” in mol/L.

BASIC reactions to remember:
Acid reactions:
acid + base salt + water
acid + metal salt + hydrogen gas
acid + carbonate carbon dioxide gas + salt + water
Formation of hydronium:
H+ + H2O H3O+
Reactions of various oxides with water:
Non-metal (acidic) oxides:
CO2 (g) + H2O (l) H2CO3 (aq) (carbonic acid)
SO2 (g) + H2O (l) H2SO3 (aq) (sulfurous acid)
2NO2 (g) + H2O (l) HNO3 (aq) + HNO2 (aq) (nitric and nitrous acid) P2O5 (g) + H2O (l) 2H3PO4 (aq) (phosphoric acid)
Metal (basic) oxides:
K2O (s) + H2O (l) 2KOH (aq) (potassium hydroxide)
Na2O (s) + H2O (l) 2NaOH (aq) (sodium hydroxide)
MgO (s) + H2O (l) Mg(OH)2 (aq) (magnesium hydroxide)
Various EQUILIBRIUM reactions:
Formation of carbonic acid: CO2 (g) + H2O (l) H2CO3 (aq)
Copper complex-ions: Cu(H2O)42+ (aq) + 4Cl־(aq) CuCl42־(aq) + 4H2O (l) Decomposition of dinitrogen tetroxide: N2O4 (g) 2NO2 (g)
Decomposition of calcium carbonate: CaCO3 (s) CaO (s) + CO2 (g) Non-Arrhenius acid/base reaction:
Gaseous hydrogen chloride and ammonia react:
HCl (g) + NH3 (g) NH4Cl (s)
IONISATION of strong and weak acids:
Hydrochloric: HCl (g) + H2O (l) H3O+ (aq) + Cl־ (aq)
Nitric: HNO3 (l) + H2O (l) H3O+ (aq) + NO3-
Sulfuric: H2SO4 (l) + 2H2O (l) 2H3O+ (aq) + SO42־
Ethanoic: CH3COOH (s) + H2O (l) H3O+ (aq) + CH3COO־ (aq)
Sources of sulfur and nitrogen oxides in the atmosphere:
Sulfur Oxides:
Organic decomposition: 2H2S (g) + 3O2 (g) 2SO2 (g) + 2H2O (l) Burning high-sulfur coals: S (s) + O2 (g) SO2 (g)
Smelting metal sulfides: 2PbS (s) + 3O2 (g) 2PbO (s) + 2SO2 Nitrogen Oxides:
Lightning: N2 (g) + O2 (g) 2NO (g)
Oxidation of nitrogen monoxide: 2NO (g) + O2 (g) NO2 (g)
Amphiprotic substances:
Sodium hydrogen carbonate:
HCO3־ (aq) + H3O+ (aq) H2CO3 (aq) + H2O (l)
HCO3־ (aq) + OH ־ (aq) CO32־ (aq) + H2O (l)
Natural Buffers:
The carbonic acid/hydrogen carbonate ion buffer in freshwater lakes: H2CO3 (aq) + H2O (l) H3O+ (aq) + HCO3־ (aq)
General word-formula:
alkanoic acid + alkanol ester + water
butanoic acid + pentanol pentyl butanoate
C3H7COOH (aq) + C5H11OH (l) C3H7COOCH2C4H9 (aq) + H2O (l)

1. Indicators were identified with the observation that the colour of some flowers depends on soil composition: RECALL:
General Properties of ACIDS:
They taste sour.
They are corrosive.
When in solution, they can conduct electricity.
Acids are neutralised by bases.
They affect the colour of certain natural and synthetic dyes (indicators). pH < 7
For LITMUS: blue  acid  red (litmus is a dye made from LICHENS). General Properties of BASES:
They usually taste bitter.
May be corrosive.
Are electrolytes (conduct electricity in solution).
Bases are neutralised by acids.
They affect the colour of indicators.
They feel slippery (bases react with oils on our skin, forming soaps). Are mainly insoluble in water (aqueous bases are called alkalis). Bases are usually metal hydroxides (e.g. NaOH) or metal oxides (e.g. MgO). pH > 7

For LITMUS: red  base  blue
Classify common substances as acidic, basic or neutral:
Common acids:
Vinegar (acetic acid), vitamin C (ascorbic acid), lemon juice (citric acid), aspirin (acetyl salicylic acid), ‘fizzy’ drinks (carbonic acid), car battery fluid (sulfuric acid). Common bases:
Drain cleaners (sodium hydroxide), household cleaners (ammonia), antacid tablets (calcium carbonate), baking powder (sodium bicarbonate), washing powder (sodium carbonate). Common neutral substances:

Pure water, table salt (sodium chloride; but NOT all salts are neutral), milk, oils and other fats, sugars. Identify that indicators such as litmus, phenolphthalein, methyl orange and bromothymol blue...
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