Powerpoint to help with unit 22

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# Powerpoint to help with unit 22 - PowerPoint PPT Presentation

Powerpoint to help with unit 22. P1 P2 M1 M2. For P1 and P2. To carry out the following practicals (and calulations on assignment):. Don’t forget the following equations:. No of moles = __ Mass (g) _ Molar mass

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### Powerpoint to help with unit 22

P1 P2 M1 M2

For P1 and P2

To carry out the following practicals (and calulations on assignment):

Don’t forget the following equations:

No of moles = __Mass (g)_

Molar mass

Concentration (mol dm-3) = _No of moles_ X 1000

volume (cm3)

Yield
• Yield: The amount of useful product made compared to the actual amount of product that is possible to be made
• A high yield means: Lots of useful product has been made.
• Formula: % yield = Actual number of moles X 100

Expected number of moles

Atom economy
• Atom economy of a chemical reaction is the measure of how much starting materials (reactants) changes into the desirable/useful product.
• A high atom economy means that the chemical reaction is efficient

% atom economy = __ molar mass desirable product__ X 100

molar mass of reactants

Making copper (II) sulfate

CuO(s) + H2SO4 (aq) CuSO4 + H2O(l)

Theoretical mass of copper (II) sulfate-5-water that can be obtained from this reaction = 12.475g

To calculate the yield you will need to do:

__Mass of copper (II) sulfate -5-water made __ X 100

Theoretical mass of copper (II) sulfate-5-water

Making copper (II) sulfate

CuO(s) + H2SO4 (aq) CuSO4 + H2O(l)

To calculate the atom economy:

% atom economy = __ molar mass desirable product__ X 100

molar mass of reactants

Molar mass of ALL reactants (CuO and H2SO4) = 178

Molar mass of desirable product = (CuSO4) = 160

Making copper (II) sulfate

CuO(s) + H2SO4 (aq) CuSO4 + H2O(l)

Hence the atom economy of copper (II) sulfate from this chemical equation:

% atom economy = __ 160__ X 100 = 89.89%

178

Making aspirin

C6H4(OH)COOH + (CH3CO)2O  C6H4COOHOCOCH3+ CH3COOH

Aspirin

(desirable product)

Making aspirin
• To calculate the atom economy:

% atom economy = __ molar mass desirable product__ X 100

molar mass of reactants

Molar mass of ALL reactants (C7H6O3 + C4H6O3) = 240

Molar mass of desirable product (Aspirin- C9H8O4) = 180

% atom economy = __ 180__ X 100 = 75%

240

Making aspirin
• Theoretical mass of aspirin that could be obtained: 2.61g

To calculate the yield you will need to do:

__Mass of Aspirin made __ X 100

Theoretical mass Aspirin

For M1:
• You need to explain the methods used:
Type of reactions carried out
• Making copper (II) sulfate-5-water is a neutralisation reaction
• Making Aspirin is an Ethanoylation reaction
Making copper (II) sulfate
• Solutions are stirred to maximise dissolving of solid chemicals
• An Excess reactant is added to ensure that ALL of the other reactant fully reacts to ensure full chemical reaction takes place (will need to specify which reactants these are)
• The solutions are filtered to remove any unreacted solid reactants (e.g. unreacted black powdered copper oxide)
• Reactants are heated to maximise amount of reactants that can react
Making copper (II) sulfate
• Evaporation is used to remove undesirable chemicals (i.e. water) from the desirable product. It is usually partially evaporated with heat for health and safety reasons and then left overnight to dry so that ALL of the water can be removed without burning some of the desirable product and changing it into a different chemical (which would decrease yield). When ALL of the water has been evaporated then the final product has been obtained
Making Aspirin
• An excess of ethanoic anhydride is added so that all of the 2-hydroxybenzoic acid reacts
• Phosphoric acid is not an actual reactant but it is a catalyst for making aspirin. It reduces the activation energy of the chemical reaction. This acid must be handled in the fume cupboard because it is an irritant to the respiratory system and the fumes can be very irritating to the eyes
Making Aspirin
• Aspirin must be made using reflux conditions. This is because the reactants themselves are very unreactive so strong reaction conditions are needed to ensure a chemical reaction takes place. In the reflux condenser any gases that form will not escape- they cold water in the lining of the condenser will condense any gases formed back into a liquid so that it falls back down into the reaction vessel (pear shaped flask). This will reduce amount of reactant that escapes which will avoid a low yield
Making Aspirin
• Water is added down the reflux condenser so that any gases that have lined/coated the inside of the condenser are washed back down into the reaction flask so that all of the reactants can react- which avoids a low yield.
Making Aspirin
• A water bath is used to gently heat the chemicals- using a flame/bunsen burner is too harsh and will burn the chemical and change it into a different chemical (which will reduce the yield). The gentle heat will ensure that the reactants have enough energy to react- this ensures that a chemical reaction takes place
Making Aspirin
• The contents/chemicals in the flask should be swirled to ensure that the reaction mixture is at a constant temperature (too avoid some chemicals being too cold to react). The swirling also helps the chemicals to mix to maximise the amount of reactants that react.
Making Aspirin
• Aspirin is mixed in and dissolved in cold water which shows that aspirin in soluble in water. This mixture of aspiring and water is placed in an ice bath to decrease the temperature of the water, which reduces the amount of spaces between the water molecules that aspirin can occupy when aspirin dissolves in the water- this will mean that aspiring can’t dissolve properly in the water as there are not enough spaces between the water molecule for it to fill up so the aspirin crystallises on top of the water
Making Aspirin
• The solid aspirin that is with the cold water is filtrated using suction filtration. This involves using a vacuum pump to “suck” / remove the water from the aspirin. This separates the Aspirin from the cold water
• During the filtration process, the aspirin is also washed with some water to wash away and remove any purities from the aspirin so that they can be “sucked” / removed away using the vacuum pump.
For M2:
• You need to identify problems in the method and explain how they could decrease yield:

Where ever you can lose chemicals then you will have less available to make your final product

Problems with methods: what can decrease yield?
• Anything that involves transferring chemicals from one container to another- YOU WILL UNINTENTIONALLY LEAVE REACTANTS BEHIND
• Anything that involves adding a reactant chemical to a solution- YOU WILL UNINTENTIONALLY ADD CHEMICALS TOO QUICKLY WHICH MEANS NOT ALL OF THE REACTANTS WILL BE ABLE TO REACT
Problems with methods: what can decrease yield?
• Anything that involves heating/boiling chemicals in an open reaction vessel: YOU WILL UNINTENTIONALLY OVERHEAT THE CHEMICALS AND SOME OF THE REACTANT WILL ESCAPE AS A GAS
• Anything that involves evaporation- YOU WILL UNINTENTIONALLY OVERHEAT AND SOME OF THE CHEMICAL WILL “SPIT” OUT OF THE EVAPORATING BASIN