C5.1 Monitoring chemical reactions

Question 1

Concentration

Answer 1

a measure of the amount of dissolved solute present in a solution

Question 2

Concentration equation

Answer 2

concentration = mass of solute ÷ volume of solution

Question 3

1dm^3

Answer 3

1 litre

1000 cm^3

Question 4

Standard solution

Answer 4

any solution with a known concentration

Question 5

How to make a standard solution

Make 250cm^3 of a 314 g/dm^3 solution of sodium chloride

Answer 5

work out how many grams of solute you need
mass = concentration x vol
314g/dm^3 x 0.25dm^3 = 75.8g

now weigh out this mass in beaker
add deionsied water to the beaker and stir until solute has dissolved
pour solution into volumetric flask ensuring all the solution is in it
top the flask up to the correct volume (250cm^3) with more deionsied water

Question 6

Titrations

Answer 6

allow you to find out exactly how much acid is needed to neutralise a given quantity of alkali (or vice versa)

Question 7

Titration method (ASSESSED PRACTICAL)

Answer 7

1) using a pipette measure out a set volume of the alkali into a flask
add a few drops of indicator - phenolphthalein or methyl orange
2) fill a burette with a standard solution of acid
3) use the burette to add acid to the alkali a bit at a time
swirl flask regularly
go slow, a drop at a time when the alkalis almost neutralised
5) indicator changes colour when all the alkali has been neutralised (end point)
6) record the volume of acid used to neutralise the alkali (called the titre)
7) repeat this process a few times and calculate mean of results

Question 8

Phenolphthalein

Answer 8

pink in alkalis

colourless in acids

Question 9

Methyl orange

Answer 9

yellow in alkalis

red in acids

Question 10

Concentration equation for mol/dm^3

Answer 10

concentration = number of moles ÷ volume of solution

Question 11

Convert concentration in mol/dm^3 into g/dm^3

Answer 11

multiply the concentration in mol/dm^3 by the relative formula mass of the solute

Question 12

Molar volume

Answer 12

the volume occupied by one mole of a gas

dm/mol^3

Question 13

Molar volume equation

Answer 13

molar volume = gas volume ÷ number of moles

Question 14

One mole of any gas occupies 24 dm^3 ( =24 000 cm^3) at…

Answer 14

room temperature and pressure

RTP = 20 °C and 1 atmosphere

Question 15

Molar volume of gasses at RTP

Answer 15

24 dm^3/mol

Question 16

Molar volume equation for gasses at RTP

Answer 16

24 = gas volume ÷ number of moles

Question 17

Yield

Answer 17

amount of product you get from a chemical reaction

Question 18

Theoretical yield

Answer 18

maximum mass it is possible to make from a given mass of reactants

Question 19

Actual yield

Answer 19

mass of products you actually make in a chemical reaction

Question 20

Percentage yield equation

Answer 20

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

Question 21

Why may the percentage yield be less than 100%?

Answer 21

the reactants react in a different way than expected
reaction did not go to completion
lose products when separating it from the reaction mixture and purifying it

Question 22

Why do industries use reactions with highest possible yield?

Answer 22

reduce waste

keep costs as low as possible

Question 23

Atom economy

Answer 23

tells you what percentage of the mass of the reactants has been converted into your desired products when manufacturing a chemical

Question 24

Atom economy equation

Answer 24

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

Question 25

Why is low atom economy bad?

Answer 25

uses up resources very quickly unsustainable - make lots of waste material that needs to be disposed of not usually profitable - raw material are expensive to buy, waste products can be expensive to dispose

Question 26

Factors considered when choosing a reaction pathway (5)

Answer 26

``` yield of product atom economy of reaction usefulness of by-products rate of reaction equilibrium position - is it reversible? ```

Question 27

By-product

Answer 27

substance formed in a reaction in addition to the desired product