C5 Seperate chemistry 1

Question 1

How do you calculate concentration?

Answer 1

conc = moles dissolved/ vol of solution

mol
dm^3

Question 2

How do you convert g/dm^3 into mol/dm^3 ?

Answer 2

divide by relative formula mass

Question 3

How do you convert mol/dm^3 into g/dm^3 ?

Answer 3

multiply by relative formula mass

Question 4

How do you calculate percentage yield?

Answer 4

% yield = (actual yield/ theoretical yield) x100

Question 5

What is the actual yield in comparison to the theoretical yield?

Answer 5

less than

Question 6

What causes the actual yield to be less than the theoretical yield?

Answer 6

• incomplete reactions
• impure reactants
• practical losses during the experiment
• unwanted side reactions

Question 7

What is atom economy?

Answer 7

% of mass of reactants that ends up being the desired product

Question 8

How do you calculate atom economy?

Answer 8

(mr of desired products/ mr of all products) x100

Question 9

What factors affect the reaction pathway of a specific product and why?

Answer 9

atom economy
-want a reaction with least waste products

yield
-want to produce as much as possible

rate
-want to make the most at fastest speed

usefulness of by-products
-want to reduce waste

Question 10

What is the molar volume of any gas at room temperature + pressure?

Answer 10

volume occupied by one mole of molecule of any gas at room temperature+pressure

volume = molar vol x moles

Question 11

How do you calculate molar volume?

Answer 11

mol vol = gas vol/ no. moles

Question 12

How can we calculate gas vol from a balanced equation?

Answer 12

1
identify product and reactant in question

2
work out no. moles of reactant

3
use the balanced equation to work out the ratio of moles between the reactant and the product

4
use ratio to work out the no. moles of the product

5
use avogadros law to work out volume of product

avogadros law:
volume = mol vol (usually 24dm3) x number of moles

Question 13

How can we use the volume of one gas to find the volume of another?

Answer 13

1
ratio the coefficient of the rectant with known volume with the product in question

2
use volume to find the volume of the product

Question 14

What is the harber process?

Answer 14

• reversible reaction

- nitrogen + hydrogen <=> ammonia

Question 15

How is the rate of attainment of equilibrium affected by changes in temperature?

Answer 15

• if temperature is increased
• dynamic equilibrium opposes this change
• by decreasing the temperature
• favours endothermic reaction
• lower temperatures mean slower RoR
• takes longer to produce same % yield of product

Question 16

How is the rate of attainment of equilibrium affected by changes in pressure?

Answer 16

• if pressure is increased
• dynamic equilibrium opposes this change
• it will do this by decreasing the number of molecules in the reaction
• increasing pressure means stronger, more expensive equipment is needed
• increases cost

Question 17

How is the rate of attainment of equilibrium affected by changes in concentration?

Answer 17

• if more reactant is added
• dynamic equilibrium opposes this change
• by decreasing amount of reactant in reaction

Question 18

How is the rate of attainment of equilibrium affected by the use of a catalyst?

Answer 18

• increases RoR

- temperatures dont need to be high to maximise % yield

Question 19

What may fertilisers contain?

Answer 19

• nitrogen
• phosphorus
• potassium

Question 20

How are fertilisers formed from ammonia and why?

Answer 20

ammonia + nitric acid -> ammonium nitrate

ammonium nitrate
-NH4NO
–has a high proportion of nitrogen per unit mass
–nitrogen good for plant growth

Question 21

How is ammonium sulphate produced by laboratory production?

Answer 21

ammonia solution + dilute sulfuric acid

stage one
-pipette 25cm3 of ammonia solution in conical flask

stage two
-titration

stage three
-mix same volumes of ammonia and sulfuric acid determined in the titration with no indicator

stage four
-preparation of pure, dry crystals of ammonium sulfate

Question 22

How is ammonium sulphate produced by industrial production?

Answer 22

• lots of stages needed
• ammonia and sulfuric acid have to be made from raw material first
• use a large reaction chamber filled with ammonia gas
• sulfuric acid is sprayed into chamber where it reacts with the ammonia
• to produce ammonium sulphate

Question 23

Describe the titration of ammonia solution with dilute sulfuric acid (ammonia solution in conical flask)

Answer 23

• add a few drops of methyl orange to the ammonia solution
• fill a burette with sulfuric acid.
• read the level of the burette
• add acid from the burette swirling gently
• add drop-by-drop near the end-point until the indicator just changes colour
• read the level in the burette and record the volume of acid used
• repeat until results are concordant

Question 24

Describe the steps of preparing pure, dry crystals of ammonium sulphate ( solution already prepared)

Answer 24

• pour solution into an evaporating dish and heat to dryness
• until pure crystals form
• leave to cool
• filter off crystals
• wash with distilled water
• leave to dry

Question 25

Why isn’t laboratory production of ammonium sulfate suitable for industrial use?

Answer 25

• volumes required are too large to titrate
• volumes of solutions are too large to be heated for evaporation
• crystallisation process is too slow