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RELATIVE ATOMIC MASS
We can use a mass spectrometer to identify the number of isotopes + abundance of
isotopes
...

Ar = (Mass of isotope x abundance) + (Mass of isotope x abundance) / 100
E
...
(28x92
...
7) + (30x3
...
1
204
...
3 x Y) + (20
...
Multiple by 100
20437 = (203 x Y) + (205 x (100-Y)
2
...
Minus the 20,500 from the original number
-63 = 203y - 205y
4
...
Divide by the y (in this case, 2)
31
...

Relative isotopic mass = The mass of one isotope compared to one twelfth of the
mass of carbon12
...

Ignore spectator ions in ionic equations
ONLY SPLIT IF AQ
E
...
BaCl2 (aq) + 2AgNO3 (aq) -> Ba(NO3)2 (aq) + 2AgCl (s)
Ba 2+ , 2Cl - , 2Ag +, 2NO3-, -> Ba2+ , 2NO32Cl- (aq) + 2Ag(aq) -> 2AgCl (s)

STOICHIOMETRY
= Mole ratio
E
...
Calculate the mass of aluminum needed to react with 150g of Chlorine
...
11268 moles
Cl2 : Al
3 : 2
n Al = n x Mr = 1
...
0g

MOLES & GASES
Gases take up a specific volume of space at RTP (room temperature & pressure, 25
degrees & 100KPa)
...


/ 1000 / 1000
cm3 -> dm3 -> m3
<
IDEAL GAS EQUATION
If the conditions are not RTP, we cannot use v=nx24, instead we use the following :
PV = nRT
P = Pressure
V = Volume
n = Moles
R = Gas constant - 8
...


WATER OF CRYSTALLISATION
Hydrated = Water molecules within the lattice
Anhydrous = No water within the lattice
Water of crystallisation = Number of water molecules

ASSUMPTIONS MADE
- All water has been lost : Sometimes water can be left inside crystals, Fixed by
heating to a constant mass
...

CaCl2
...
573g
3
...
24g
CaCl2

H2O

3
...
24g

111
...
03

0
...

= Mass of actual product
/
x 100
Mass of theoretical product
WHY?
- Transfer of materials from materials
- Reaction may be irreversible / incomplete
Excess = Bigger number
Limiting = Controls how much product is made

ATOM ECONOMY
% Atom economy = total Mr of desired product
/
total Mr of all reactants

STANDARD SOLUTION
Standard solution is the solution of a known concentration
...
Transfer between 4
...
4 g of potassium hydrogen phthalate into a weighing
bottle and weigh it to the nearest 0
...

2
...
Carefully transfer the bulk of
the potassium hydrogen phthalate from the weighing boat into the beaker
...
Reweigh the boat with any remaining potassium hydrogen phthalate to the
nearest 0
...

4
...

5
...
Rinse the
beaker well, making sure all liquid goes into the volumetric flask
...
Add distilled water until the level is within about 1 cm of the mark on the neck of
the flask
...

7
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Insert the stopper and shake thoroughly ten times to
ensure complete mixing
...

8
...
Leave a space for the
concentration to be filled in after you have calculated it
...


TITRATION
1
...
The other solution is placed in the burette
3
...
The tap on the burette is carefully opened and the solution added, portion by
portion, to the conical flask until the indicator just changes colour(this is the end
point)
5
...

In compounds the total of all oxidation numbers is zero
In polyatomic ions, the total of all the oxidation numbers is equal to the charge on
the ion
...

Fluorine always adopts the -1 oxidation state
Aluminium always adopts the +3 oxidation state
Hydrogen always adopts the +1 state in its compounds unless it is bonded to a
metal (then it’s -1)
Oxygen always adopts the -2 state in its compounds unless it is with fluorine
(then its positive) or it is with a peroxide
...
We can describe it in terms of electrons or in terms of
oxidation number
...

Reducing agent - one being oxidised : Donates electrons
Oxidising agent - one being reduced : Accepts electrons

GROUP 2 COMPOUNDS
Group 2 oxides react with water to form a solution of the metal hydroxide
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TRENDS
- Ionisation energy decreases down a group : There is more shielding with a
larger atomic radius as you decrease down the group so IE decreases down the
group
- The radius increases down the group : There are more shells as there is an
increased number of electrons and therefore the radius increases
...

All group 2 hydroxides are alkali as when they are dissolved in water, they release OHions
...

Calcium oxidised and hydroxide is used to neutralise acidic soil
...

Out of Cl2, Br2 and I2, Chlorine is the best (strongest) oxidising agent (it’s good at
accepting electrons
...

Uses of Chlorine
1
...
g
...

Problems - Chlorine is toxic, Suspected of reacting with organic compounds to
form halogenated organic molecules that can be carcinogenic
...
Making bleach
- Cl2 + 2NaOH -> NaCl + NaClO + H2O
Conditions :
- Cold
- Dilute (aq)
If these are changed you make sodium chlorate (V) not sodium chlorate (I)
- 3Cl2 + 6NaOH -> 5NaCl + NaClO3 + 3H2O

ENTHALPY CHANGES
Exothermic = Negative ΔH
Endothermic = Positive ΔH
Enthalpy level diagram
EXOTHERMIC

Heat energy goes to surroundings e
...
thermometer

ENDOTHERMIC

Bond enthalpies
BONDS BROKEN - BONDS MADE

Average bond enthalpy
= The energy required to break one mole of a specified type of bond in a gaseous
molecule
-

Bond breaking is ENDOTHERMIC as energy is required
Bond making is EXOTHERMIC as energy is released

LIMITATIONS
- All molecules need to be gaseous
- As you’re using average bond enthalpies, the actual energy would be slightly
different
...


REACTANTS -> COMBUSTION PRODUCTS = ROUTE A / DIRECT
REACTANTS -> PRODUCTS = ROUTE B / INDIRECT
REACTANTS -> PRODUCTS -> COMBUSTION PRODUCTS = ROUTE C / INDIRECT
A=B+C

EXPERIMENTAL ERROR
Difference in result / True value X 100
% Error =
Error of equipment / Measurement X 100
E
...
Balance -+ 0
...
01 x 2 / m of reactant
SOURCE
- Heat loss to surroundings from spirit burner - wick
- Evaporation of water
- Evaporation of alcohol

-

Incomplete combustion
Not standard conditions

Reducing heat loss
- Drought shield which keeps the heat in one direction



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Title: foundations in chemistry
Description: notes on a level chemistry, made by an A student

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