SC14,SC15 & SC16

Question 1

How do you calculate the theoretical yield?

Answer 1

RAM x balancing number

Question 2

What is percentage yield?

Answer 2

Compares the actual yield and the theoretical yield

Percentage yield= actual yield/theoretical yield x 100

Question 3

Name 1 reason why the yield is less than expected?

Answer 3

The reaction may be incomplete so not all reactants are used up

Possibly because reaction has been left for too long or reaction reached equilibrium

Question 4

Name the second reason why the yield is sometimes less than expected?

Answer 4

Some of the product is loss

Question 5

Name a third reason why the yield is less than expected?

Answer 5

May be unwanted side reactions taking place

E.g. some reactants may react to make a different product so compete with the main reaction

Question 6

What does a high percentage yield mean?

Answer 6

Higher percentage yield=more useful the reaction

Fewer raw materials are used to make the small amount of product

Question 7

What is atom economy?

Answer 7

A method of showing how efficiently a particular reaction makes use of the atoms in the reactants

Question 8

What is the formula to work out atom economy?

Answer 8

RAM of useful product/sum of RAM of all reactants x 100

Question 9

Can reactions have a high percentage yield but a low atom economy?

How can you improve atom economy if so?

Answer 9

Yes they can and it means that waste by products are formed

Atom economy can be improved by finding uses for the by products of the reaction

Question 10

What are some of the other factors when scientists must consider when deciding a reaction pathway?

Answer 10

Raw materials, temperature, pressure, catalyst, rate of reaction, purity

Question 11

What is the concentration of a solution?

Answer 11

It is the amount of solute dissolved in a stated volume of solution

Question 12

How do you calculate concentration in g dm-3

Answer 12

Mass of solute in g/volume of solution in dm3

Question 13

What do you do if the volume of the solution is given in cm3?

Answer 13

Divide by 1000

Question 14

What is the equation triangle for working out concentration?

Answer 14

Mass (g)

Concentration (g dm-3) x volume (dm3)

Question 15

How do you calculate concentration in mol dm-3?

Answer 15

Number of moles on solute/ volume of solution in dm3

Question 16

What equation relates both types of concentrations?

Answer 16

Concentration in g dm-3/ RAM of solute

Question 17

What is the equation triangle for converting concentration?

Answer 17

Concentration (g dm-3)

Concentration (mol dm-3) x RAM

Question 18

What does Avogadro’s law state?

Answer 18

If the temperature and pressure are the same, equal volumes of different gases contain an equal number of molecules

Question 19

What is the molar gas volume?

Answer 19

It is the volume occupied by one mole of molecules of any gas

It is 24dm3 or 24000cm3 at room temperature and pressure

Question 20

What is the equation for the volume of gas?

Answer 20

Amount of gas (mol) x molar volume

Question 21

How do you calculate the amount of gas if you know the volume?

Answer 21

Volume of gas/molar volume

Question 22

What do fertilisers do?

Answer 22

They replace the mineral ions needed by plants and so promote plant growth

Question 23

What are some of the important elements used in fertilisers?

Answer 23

Nitrogen, phosphorus and potassium

Fertiles must provide them as soluble compounds so the root hair cells only absorb mineral ions dissolved in water

Question 24

How is ammonium nitrate produced?

Answer 24

Salt manufactured by reacting ammonia solution with dilute nitric acid

Question 25

How is nitric acid manufactured?

Answer 25

Ammonia + oxygen -> nitric acid + water

Question 26

How is ammonium sulfate produced?

Answer 26

Made in the laboratory by reacting ammonia sulfate with dilute sulfuric acid

Question 27

How does the production of ammonium sulfate differ in a laboratory to it being produced on an industrial scale?

Answer 27

Laboratory - small scale
Start with ammonia sulfate and dilute sulfuric acid
Made through titration, then crystallisation in a batch process

Industrial- large scale
Raw materials for making ammonia and sulfuric acid
Made in several stages in a continuous process

Question 28

How does the preparation differ in each process?

Answer 28

Laboratory
Ammonia solution and dilute sulfuric acid bought from chemical manufacturers

Industrial
Substances made on site from raw materials

Question 29

What is the difference between a batch process and a continuous process?

Answer 29

Batch (difficult to automate)
Small amount made, apparatus cleaned, then repeated

Continuous (automated)
Reactants are constantly fed into reactors and products removed
Need fewer people to make a given amount of product

Question 30

What happens in dynamic equilibrium?

Answer 30

The forward and backward reactions still happen, at the same rate
The concentrations of all reacting substances don’t change

Question 31

What happens if the temperature is increased?

Answer 31

Moves in the direction of the endothermic reaction

Time taken it reach equilibrium decreases

Question 32

What happens if the pressure is increased (in a reaction involving gas)?

Answer 32

Moves towards the side of the balanced equation with the fewer molecules of reacting gas
Time take to reach equilibrium decreases

Question 33

What happens if the concentration of a reacting substance increases?

Answer 33

It moves away from the reacting substance in the balanced equation
Time taken to reach equilibrium decrease

Question 34

What happens if a catalyst is added?

Answer 34

There in no change in the position if equilibrium

Time taken to reach equilibrium decreases

Question 35

What happens if the pressure is increased in the barber process?

Answer 35

The position of equilibrium moves to the right as there are fewer molecules on this side

Question 36

How do high pressures effect the equilibrium yield?

Answer 36

It increase the equilibrium yield of ammonia and increase the rate of reaction

However, very high pressures are too expensive to maintain

Question 37

If the temperature increases in the harder process, does the equilibrium move towards the left or right?

Answer 37

It moves to the left in the direction of the endothermic reaction

Question 38

What is the temperature used in the Harber process?

Answer 38

450 C

Low temperature increase equilibrium yield of ammonia but reduce rate of reaction

Question 39

Why is an iron catalyst used in the Harber process?

Answer 39

It doesn’t change the position of equilibrium but increases the rate of reaction

Question 40

What are factors taken into account when choosing reaction pathways?

Answer 40

Availability and cost of raw materials and energy supplies
Rate of reaction and the equilibrium position
Atom economy, yield and usefulness of by products

Question 41

What does a simple chemical cell have?

Answer 41

2 different metals, each dipped into a solution of one of their salts
A ‘salt bridge’ to allow dissolved ions to pass from 1 solution to the other

Question 42

When is the voltage greater?

Answer 42

The voltage is greater when the further apart in the reactivity series the 2 metals are