C5 - Monitoring and Controlling Chemical Reactions

Question 1

What is concentration?

Answer 1

A measure of how much solute you dissolve in s given volume

Question 2

What units is concentration measured in?

Answer 2

1) g/dm³

2) mol/dm³

Question 3

State the formula used to find the concentration from the mass of solute.

Answer 3

mass of solute (g) = concentration (g/dm³) x volume of solution (dm³)

Question 4

How do you convert from g/dm3 to mol/dm3?

Answer 4

Divide the concentration in g/dm³ by the relative formula mass of the solute

Question 5

What is a standard solution?

Answer 5

Any solution that you know the concentration of

Question 6

Why are titrations used?

Answer 6

To find out exactly how much acid is needed to neutralise a given quantity of alkali

Question 7

How do you carry out a titration?

Answer 7

1) Using a pipette, measure out a set volume of the alkali into a flask. Add a few drops of an indicator - usually phenolphthalein or methyl orange
2) Fill a burette with a standard solution of acid
3) Use the burette to add the acid to the alkali a bit at a time. Swirl the flask regularly. Go slowly ( a drop at a time) when the alkali’s almost netralised
4) The indicator changes colour when all the alkali has been neutralised (this is called the end point)
5) Record the volume of acid used to neutralise the alkali (called the titre)
6) Repeat this process a few times, making sure you gt very similar results each time. You can then take the mean of your results

Question 8

What colour is phenolphthalein in alkakis and acids?

Answer 8

1) pink in alkalis

2) colourless in acids

Question 9

What colour is methyl orange in alkalis and acids?

Answer 9

1) yellow in alkalis

2) red in acids

Question 10

State the formula used to find concentration in mol/dm3.

Answer 10

number of moles (n) = concentration (mol/dm³) x volume of solution (dm³)

Question 11

What is molar volume?

Answer 11

The volume occupied by one mole of a gas

Question 12

What units is molar volume measured in?

Answer 12

dm³/mol

Question 13

State the formula used to calculate molar volume.

Answer 13

number of moles (n) = gas volume (dm³) / molar volume (dm³/mol)

Question 14

What volume does one mole of any as always occupy at room temperature and pressure (RTP)?

Answer 14

24dm³

Question 15

What is RTP?

Answer 15

1) 20°C

2) 1 atmosphere

Question 16

What is yield?

Answer 16

The amount of product you get from a reaction

Question 17

State the formula used to calculate percentage yield.

Answer 17

percentage yield = (actual yield/theoretical yield) x 100

Question 18

What is theoretical yield?

Answer 18

The mass of product you would make if all the reactants were converted to products

Question 19

Why is it important to use reactions with the highest yield possible?

Answer 19

1) to reduce waste

2) to keep costs as low as possible

Question 20

What is atom economy?

Answer 20

What percentage of the mass of the reactants has been converted into your desired product

Question 21

State the formula used to calculate atom economy.

Answer 21

atom economy = (total Mr of desired products/total Mr of desired products) x 100

Question 22

What factors need to be considered in industry?

Answer 22

1) the percentage yield of the reaction
2) the rate of reaction
3) whether the reaction is reversible

Question 23

What is the rat of a reaction?

Answer 23

How quickly a reaction happens

Question 24

State the formula used to calculate the rate of reaction.

Answer 24

rate of reaction = amount of reactant used or amount of product formed / time

Question 25

List some ways that the rate of a reaction can be measured?

Answer 25

1) precipitation
2) change in mass
3) the volume of gas given off

Question 26

How would you measure the rate of a reaction by recording precipitation?

Answer 26

1) mix the two reactant solutions and put the flask on a piece of paper that has a mark on it
3) observe the mark through the mixture and measure how long it takes for the mark to be obscured. The faster it disappears, the faster the reaction

Question 27

How would you measure the rate of a reaction by recording change in mass?

Answer 27

1) measure the rate of a reaction that produces a gas using a mass balance
2) the quicker the reading on the balance drops, the faster the reaction
3) you can use your results to plot a graph of change in mass against

Question 28

How would you measure the rate of a reaction by recording the volume of gas given off?

Answer 28

1) use a gas syringe to measure the volume of gas given off
2) the more gas given off during a set time interval, the faster the reaction
3) you can use your results to plot a graph of gas volume against time elapsed

Question 29

How does surface area affect reaction rate?

Answer 29

The greater the surface area of the solid reactants, the faster the reaction

Question 30

How does concentration affect reaction rate?

Answer 30

The higher the concentration, the faster the reaction