C7 revision

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C7 revision
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Alkanes

• Alkanes are hydrocarbons.
• A hydrocarbon is made up ONLY
• of CARBON and HYDROGEN

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Structure and formula

• Alcohols are a group of organic compounds which
  have an OH group at the end of a carbon chain.

Methanol Ethanol
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Uses

• Methanol
• Used as a chemical feedstock to make other
  chemicals
• (turned into adhesives, foams, solvents,
  windscreen washer fluid)
• Ethanol
• Used a solvent in cosmetics (it evaporates
  easily) and perfumes.
• Used as a fuel as it burns well
• Used in beverages its what makes drinks
  alcoholic.

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Properties of the OH group

• The OH group gives alcohols some properties.
• e.g. methanol and ethanol are liquids at room
  temperature
• Methanol and ethanol will mix with water
• (alcohols with large carbon chains wont as the
  hydrocarbon part dominates)

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Reaction of sodium and alcohol
2
-
2
2Na
Na
H2
Sodium ethoxide
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Carboxylic acids

• Carboxylic acids are organic acids.
• They contain the elements COOH arranged as below

Their names end in oic acid
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Making Vinegar

• Vinegar is ethanoic acid. It is made by allowing
  ethanol to oxidise.
• ethanol ? ethanoic acid
• This turns beer into malt vinegar, and wine to
  wine vinegar.

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Acidity

• Carboxylic acids are weak acids.
• They are only partially ionised

H
O

-
-C
C
H
H
O
-H
H
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Reactions

• Carboxylic acids react as all acids do.
• Acid metal ? salt hydrogen
• Acid soluble hydroxide ? salt water
• Acid metal carbonate ? salt water
• 
  carbon dioxide

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Esters

• Esters are used as flavours and scents in foods
  and perfumes. They are also used as solvents and
  plasticisers.

O
C
CH3
CH3
CH2
O
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Esters are made when an alcohol reacts with a
carboxylic acid. A small amount of concentrated
sulphuric acid is used as a catalyst. They are
heated together under reflux.
O

H2O
C2H5-OH
C-CH3
O

C-CH3
C2H5 -O
H-O
Alcohol Carboxylic acid
Ester water
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Most oils and fats are esters of glycerol and
carboxylic acids with long chains. (also known as
fatty acids).
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This is a short hand way of writing the
structures. It is easier to draw for larger
molecules.
The ones with double bonds are unsaturated fats,
the ones with no CC are saturated fats.
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Exothermic and Endothermic Reactions

• In an exothermic reaction energy is released from
  the reaction to the surroundings. i.e. the
  products are at lower energy than the reactants.
  It can be shown in a graph called an energy level
  diagram. The reverse is true for endothermic
  reactions.

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• Hydrogen burns in air to form steam
• 2H2 O2 ? 2H2O
• Work out the energy change for the reaction, then
  draw an energy level diagram to show if it is
  exothermic or endothermic.

H2 contains a H-H bond, O2 has a double bond
OO H2O has 2 O-H bonds
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• 2H2 O2 ? 2H2O

H-H
H-O-H
OO
H-O-H
H-H
2 x 436
498

4 x 464


1370
1856
Releases Energy
Uses Energy
EXOTHERMIC
1370 1856 -486

kJ/mol
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Measurement Uncertainty

• Results are usually given within a range.
• E.g. purity of a drug is given as 99.10.2
• What is the lowest and highest purity it could
  be?
• The actual value will lie between these values.

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Types of error

• Sometimes an error will be because of the
  equipment. E.g. a pipette will measure
  25cm30.06cm3. Every time the pipette is used
  this will be the same error.
• This is known as a systematic error.
• If you take the reading incorrectly, this could
  happen differently every time, this is called a
  random error.

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Titration Procedure

• Acid is placed in a burette
• A pipette is used to place 25cm3 of alkali into a
  conical flask
• One or two drops of indicator are added to the
  alkali
• Acid is run into the flask until the indicator
  changes colour. This is a rough value
• The titration is done again, but adding the acid
  dropwise at the end point.
• The accurate titration is repeated

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• Calculate the concentration of sodium carbonate
  in the following
• a) 100g in 1dm3
• b) 10g in 100cm3
• c) 250g in 2dm3
• d) 50g in 250cm3
• e) 17.4g in 197cm3

100g/dm3
100g/dm3
1dm3 1000cm3
125g/dm3
200g/dm3
88.3g/dm3
Concentration mass (g)
volume (dm3)
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• HCl NaOH ? NaCl H2O
• What concentration is the NaOH, if 25cm3 of it
  requires 12.5cm3 of 36.5g/dm3 HCl to neutralise
  it.

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• HCl NaOH ? NaCl H2O

40g
36.5g
Write down the formula mass in g.
Work out the amount in grams of the
acid. (12.5cm3 of 36.5g/dm3)
If 36.5g of HCl reacts with 40g of NaOH then
0.456g reacts with
36.5 x 12.5 1000
0.456
This is the amount in 25cm3 or 0.025dm3 so the
concentration is -
0.456 x 40 36.5
0.50g NaOH
0.5 0.025
20cm3
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Calculations
10cm3 of sodium hydroxide (NaOH) was neutralised
by 15cm3 of nitric acid (HNO3) of concentration
6.3g/dm3. What concentration was the NaOH?
HNO3 NaOH ? NaNO3 H2O
Step 1 Write the formula masses underneath in
grams.
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10cm3 of sodium hydroxide (NaOH) was neutralised
by 15cm3 of nitric acid (HNO3) of concentration
6.3g/dm3. What concentration was the NaOH?
HNO3 NaOH ? NaNO3 H2O
63g
40g
18g
85g
Step 2 15cm3 of nitric acid of concentration
6.3g/dm3 contains how many g of acid?
6.3g/dm3 has how many g in 1cm3?
6.3/1000
So in 15cm3?
6.3 x 15/1000
0.0945g
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10cm3 of sodium hydroxide (NaOH) was neutralised
by 15cm3 of nitric acid (HNO3) of concentration
6.3g/dm3. What concentration was the NaOH?
HNO3 NaOH ? NaNO3 H2O
63g
40g
0.0945g of acid
From the equation 63g of acid reacts with 40g of
alkali so..
0.0945x40 63
0.06g of alkali in 10cm3
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10cm3 of sodium hydroxide (NaOH) was neutralised
by 15cm3 of nitric acid (HNO3) of concentration
6.3g/dm3. What concentration was the NaOH?
HNO3 NaOH ? NaNO3 H2O
63g
40g
0.06g of alkali in 10cm3
0.06x1000 10
So in 1dm3
6.0g/dm3
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Chromatography

• There are 3 main types of chromatography paper,
  thin layer and gas.
• They all work on the same principle.
• It is used to
• Separate and identify chemicals in a mixture
• Check the purity of a chemical
• Purify small samples of a chemical

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Thin Layer Chromatography
Lid used to stop solvent from evaporating
A solvent (substance which will dissolve some
solids) acts as the mobile phase and moves up the
plate.
Used to analyse dyes in food products and
clothing fibres. Used to test for controlled
drugs especially cannabis.
A thin layer of a solid is coated onto a glass or
plastic sheet. This solid acts as the stationary
phase.
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Solvent front
Reference samples Spots 1-5
When the solvent gets near to the top of the
plate, it is removed from the tank and left to
dry. The position of the solvent front is marked
(where the solvent got up to). Sometimes spots
might be invisible and need to be developed by
spraying it with a chemical. Reference spots are
used to compare the unknown sample.
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Identifying chemicals (H)
Solvent front

• Some chromatograms are simply compared to
  reference samples.
• It is more accurate to identify a chemical by its
  retardation factor (Rf).
• Rf distance moved by chemical (Y)
• distance moved by solvent (X)

X
Y
If Y 5 and X 10
Rf 0.5
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Atom Economy

• The term atom economy relates to how efficient a
  reaction is. (the greater the atom economy the
  less wastage and therefore the greener the
  reaction.
• Atom economy mass of atoms in product x100
• mass of atoms in
  reactants

Note Only the useful product used for calculation
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The chemical industry

• Bulk chemicals made on a large scale
• (ammonium sulphuric acid, sodium hydroxide,
  phosphoric acid)
• Fine chemicals made on a small scale.
• (drugs, food additives, fragrances)

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Green chemistry

• Sustainability depends upon
• Renewable feedstock
• Atom economy
• By-products and waste materials
• Energy inputs or outputs
• Environmental impact
• Health and safety
• Social and economic benefits

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Three methods for making ethanol

• Made on industrial scale as a fuel, solvent and
  feedstock
• Made by fermentation (limit on concentration of
  the ethanol) can be concentrated by
  distillation
• (Fermentation requires optimum temperature and
  pH)
• Made by modified E-coli bacteria. Bacteria
  convert waste biomass into ethanol.