Entire AS Level chemistry content including Sections 3.1.1 to 3.1.7 of Physical chemistry, sections 3.2.1 to 3.2.3 of Inorganic chemistry and sections 3.3.1 to 3.3.6 of Organic chemistry content (not in that exact order). Notes are compressed and to be treated like flashcards, reading the question ...
Year= 12 Chemistry Revision with STANDARD ANSWERS
Key info
Charges + Elements + Compounds to remember
Simple Simple molecular Ionic compounds Giant covalent Giant
molecular compounds elements covalent
elements compounds
H2 CO2 – carbon NH4+ = Ammonium C= diamond, SiO2 =
O2 dioxide H2CO3 = carbonic acid graphite silicon
N2 CO- carbon HCL = hydrochloric C60 = fullerene dioxide
F2 monoxide acid
Cl2 NO2- nitrogen H2SO4 = sulfuric acid
Br2 dioxide HNO3= nitric acid
I2 NO- nitrogen H3PO4= phosphoric
P4 monoxide acid
S8 SO2- sulfur dioxide CO32- = carbonate ion
SO3- sulfur trioxide SO42- = sulfate ion
NH3- ammonia PO43- = phosphate ion
CH4- methane
H2S- hydrogen
sulfide
General reaction
Substance + oxygen = oxides
Metal + water = metal hydroxide + hydrogen
Metal + acid = salt + hydrogen
Oxide + acid = salt + water
Hydroxide + acid = salt + water
Carbonate + acid = salt + water + carbon dioxide
Hydrogencarbonate + acid = salt + water + carbon dioxide
Ammonia + acid = ammonium salt
Metal carbonate = metal oxide + carbon dioxide (on heating)
Ionic equations
How do you form an ionic equation?
1. Write out all the ions in the equation
2. Cross out the ions that don’t change (reduce or oxidise) called the spectator ions
3. Write out the ionic equation
· If we are given the precipitate formed at the end, we can work out the ions from there
· Include state symbols/.l
· Some ionic equations can be learnt e.g.;
Acid + metal hydroxide H+(aq) + OH-(aq) = H2O(l)
Acid + metal carbonate 2H+(aq) + CO32-(aq) = CO2(g) + H2O(l)
, Empirical formula
What is the definition of the empirical formula?
The empirical formula gives the simplest whole number ratio of atoms of each
element in the compound
How would you work out the actual molecular formula of a compound?
You would find the actual Mr and the empirical formula. There would be a ratio in
which the molecular formula could be double, triple etc. Of the empirical formula so
you multiply the number of each element by the ratio
How would you work out the empirical formula?
1. Find the empirical formula of 80% C and 20% H
Moles of C= 80/12 = 20/3
Moles of H = 20/1 = 20
Empirical ration= 20/3:20
Divide both sides by smallest number= 1:3 so CH3
b.) If the actual Mr of the substance is 30 then what is the actual molecular formula?
Mr of CH3 = 15
30/15=2
CH3 x 2 = C2H6
2.) How would you simplify difficult ratios like 1.66:1
First multiply by 100 to get rid of decimals 166:100
Keep multiplying until you get to a value that you can round up
(166:100) x 3= 498:300. This can be written as 500:300
Ratio = 5:3
Gas calculations
How does volume relate to pressure?
Pressure is proportional to the inverse of volume
How does temperature relate to volume?
Temperature is proportional to volume
How does temperature relate to pressure?
Temperature is proportional to pressure
How does the number (moles) relate to volume?
The moles is proportional to the volume
What equation do we use to do gas calculations?
How do we convert degrees Celsius to Kalvin?
Add 273 to the degrees
This is because 273 degrees is absolute zero, where all molecular molecules stop
working
,How do you convert KPa into Pa?
Multiply the KPa by 1000
How do you convert cm3 and dm3 into m3?
Divide by 106 for cm3 into m3
Divide by 103 for dm3 into m3
Why is volume directly proportional to moles?
In any element, the number of moles (Avogadro's constant) will occupy the same
volume. So, when dealing with calculations, we can assume the moles and the volume
are the same.
Only gases count as one mole of gaseous elements take up the same volume
E.g. What volume of oxygen is required to burn the following gases, and what volume of CO2
is produced?
750 cm3 of benzene, 2C6H5(g) + 15O2(g) = 12CO2(g) + 2H2O(l)
2 moles, 15 moles, 1 mole
Since the 750 is 2 moles, to get to 15 moles of oxygen, you multiply the 750 by 7.5 (as
2x7.5=15). So oxygen is 5625 cm3
CO2= 750x6= 4500 cm3
E.g. 100cm3 of methane was reacted with 500 cm3 of oxygen. What is the total volume of all
gases at the end, and indicate how much there is of each gas?
CH4(g) + 2O2(g) = CO2(g) + 2H2O(l)
100cm3 500cm3
1 mol 2 mol 1 mol
1 vol 2 vol 2 vol
Since methane has the smallest volume, it is limiting so 100x (the 2 moles of oxygen)
gives oxygen 200cm3 of volume
CO2 will have 100 cm3
500-200= 300cm3 excess
300+100= 400cm3 all together
Mr of a volatile liquid
What is a volatile liquid?
· A liquid with a very low boiling point that ignites and vaporizes quickly
What equation can be used to show the mr of a liquid?
· This is because PV=nRT
· The n (moles)= mass/Mr
· So PV= massRT/Mr
· Therefore Mr= massRT/PV
What is the method for calculating the Mr of a volatile liquid?
1. Draw a small volume of air into a gas syringe for a starting volume
2. Seal the end with a stopper
3. Place the gas syringe in a hot water bath and note the volume of trapped air
4. Measure the temperature of the water bath
, 5. Draw around 1 ml of hexane (a volatile gas) into a hypodermic syringe
6. Weigh the hypodermic syringe with the hexane
7. Inject the hexane into the hot gas syringe
8. Return the gas syringe into the water bath
9. Reweigh the hypodermic needle and hexane
10.Allow the volume of vapour in the gas syringe to equilibrate (reach a steady
temperature)
11. Record the final volume
Temp: 89oC = 362 K
Mass of hexane= 0.2g = 0.00020kg
R= 8.31
V= 61.5cm3 = 61.5x10-6
P=100KPa
Equation: 0.0002x8.31x362/100x61.5x10-6 = 97.83
How do you calculate the experimental error?
Actual Mr of hexane (C6H14)= (12x6)+(1x14) = 86
97.83-86/86 = 13.76%
What could be the sources of errors?
Apparatus error (balance, gas syringe)
Measuring volume of gas out of water bath (volume decreases)
Some liquid or vapour may escape from hypodermic needle as it is not sealed. This
may decrease the mass
The gas syringe may not have equilibrated
Solution calculations
What is the equation for concentration with units?
How would you calculate the concentration in g/dm 3?
Multiply the concentration in mol/dm3 by the Mr
What are the steps in calculating an unknown concentration in a titration?
Find the moles of the substance with the known concentration and vol.
Find the moles of the substance with the unknown concentration using the ratio
Find the concentration by multiplying the moles by the volume
Standard solutions
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