topic 5 - quantitative analysis

Question 1

titration

Answer 1

method of analysing the concentrations

allows you to find exactly how much acid is required to neutralise a given quantity of alkali or vice versa

Question 2

pipette

Answer 2

measures one volume of solution

fill to above the line and then carefully drop the level down

Question 3

burette

Answer 3

measures different volumes of solution
add solution drop to drop
scale down side of burette shows volume used

Question 4

how to carry out a titration (8)

Answer 4

1) use pipette to measure out a set volume of alkali into flask
2) add a few drops of indicator (not universal, should be specific)
3) fill burette with standard solution of acid
4) use burette to add acid to alkali little by little at a time, swirling the flask regularly (when close to neutralisation, only add one drop at a time)
5) indicator changes colour once alkali is neutralised
6) record volume of acid used to neutralise - known as the titre
7) repeat process making sure to get similar results every time
8) calculate the mean

Question 5

standard solution

Answer 5

solution of known concentration

Question 6

molar concentration

Answer 6

concentration = number of moles/volume of solution

Question 7

units concentration and conversion to mass concentration

Answer 7

mol/dm^-3

mol/dm^-3 to g/dm^-3 : multiply concentration by the RFM

Question 8

how to calculate the concentration of another substance

Answer 8

work out moles of known substance using moles = concentration x volume
use balance equation to work out moles of other substance you should hve
work out concentration using concentration = moles / volume

Question 9

molar volume

Answer 9

the volume occupied by one mole of gas

Question 10

molar volume units and formula

Answer 10

dm^3mol^-1

molar volume = gas volume / number of moles

Question 11

avogadro’s law

Answer 11

under the same conditions, the same number of moles of different gases all occupy the same volume

one mole of any gas always occupies 24dm^3 at room temperature and pressure (20°C and 1atm)

Question 12

atom economy definition

Answer 12

the percentage of reactants changed to useful products

Question 13

atom economy formula

Answer 13

(total Mr of desired products / total Mr of all products) x 100

Question 14

100% atom economy meaning

Answer 14

all atoms in the reactants have been turned into useful products

Question 15

reactions with low atom economies

Answer 15

they use up resources very quickly
make lots of waste products that need to be disposed of, tending to make reactions unsustainable
usually aren’t profitable as raw materials are expensive and disposing of waste materials is also expensive if done properly

Question 16

way of dealing with the problem of waste products

Answer 16

use the waste products

choose a reaction that makes the desired product and also useful byproducts

Question 17

percentage yield

Answer 17

the amount of product made compared to what should have been made

if there is a low percentage yield, lots of reactants will be wasted

Question 18

percentage yield formula

Answer 18

(actual yield/ theoretical yield) x 100

Question 19

hypothetical yield

Answer 19

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

Question 20

what 3 factors can affect yield

Answer 20

incomplete reactions
practical losses
unwanted reactions

Question 21

explain incomplete reactions as a factor that can affect yield

Answer 21

if not all of the reactants are converted to product, the reaction is incomplete and yield will be less than expected

Question 22

explain practical losses as a factor than can affect yield

Answer 22

you lose a little bit when transferring chemicals between containers

Question 23

explain unwanted reactions as a factor than can affect yield

Answer 23

if unwanted side reactions happen, yield decreases

unwanted reactions can be cause by impurities in reactants or changes to reaction conditions

Question 24

4 factors to consider in industry

Answer 24

• atom economy
• percentage yield
• rate of reaction (must be fast enough to produce the amount needed in a sensible amount of time)
• if the reaction is reversible ( to keep yield high, you may need to alter the equilibrium position by changing conditions)