Chemistry EMPA revision

Originally written for the AS EMPA in 2013 but most can be applied to any AS EMPA.

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Chemistry EMPA revision
Reactions of carbonates:
Metal carbonate Metal oxide + Carbon dioxide
o CaCO3 CaO + CO2
Metal carbonate + Acid Salt + Water + Carbon Dioxide
o CaCO3 + H2SO4 CaSO4 + H2O + CO2
Enthalpy change:
Enthalpy of formation: Enthalpy change when one mole of a substance is formed
from its constituent elements in their normal states.
Enthalpy of combustion: Enthalpy change when one mole of a substance
undergoes complete combustion in oxygen.
Average enthalpy change: The average enthalpy change when a substance
undergoes a reaction under 298K and 100kPa.
Enthalpy of formation = H Products ­ H Reactants
Enthalpy of combustion = H Reactants ­ H Products
Q = mc T
Q= J, m = g, c = 4.18 Jg-1K-1, T = Change in water/ solution temperature K or oC.
Titration, method and volumetric solutions:
1. Fill a burette with the acid of unknown concentration.
2. Accurately measure an amount of the alkali using a calibrated pipette and pipette
filler.
3. Add the alkali to a conical flash with a few drops of a suitable indicator.
4. Run in acid from the burette until the colour just changes, showing that the
solution in the conical flash is now neutral.
5. Repeat the procedure until two values for the volume of acid used at
neutralisation are the same, within experimental error.
Number of moles = concentration x volume (cm3)
1000
Calculations:
Ar = Average mass of one atom of an element
1/12th mass of an atom of 12C
Mr = Average mass of one molecule
1/12th mass of an atom of 12C
Number of moles = Mass (g)
Mass of 1 mole (g)
PV=nRT

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P = Pa, V = m3, T = K, R = 8.31 JK-1 mol-1.
o Rearrange to make:
V= nRT
P
n = PV
RT
Empirical formula = Mass or percentage of element
Ar
o Divide both answers by the smallest.…read more

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Colourless Brown.
Carbon dioxide = Bubble gas through lime water and turns it milky.
CO2 (g) + Ca(OH)2 (aq) CaCO3 (s) + H2O (l)
Sulphur dioxide SO2 = Turns damp blue litmus paper red
Turns litmus solution blue
Bubbles through potassium dichromate (VI) solution.
2H (aq) + 3SO2 (g) + Cr2O72- (aq) 2Cr3+(aq)+3SO42-(aq)+H2O(l)
+
Orange Green
Hydrogen chloride HCl = Turns damp blue litmus paper red.
Forms white fumes with concentrated ammonia.
Ammonia NH3 = Turns damp red litmus paper blue.…read more

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