Unit 3 KA6 - chemical analysis

Question 1

what is titration used for?

Answer 1

to accurately determine the volumes of solution required to reach the endpoint of a chemical reaction

Question 2

what is an indicator used for?

Answer 2

to show when the endpoint is reached

Question 3

what is a standard solution?

Answer 3

a solution of an accurately known concentration

Question 4

why are rough titrations carried out?

Answer 4

until concordant results are achieved?

Question 5

what number range is considered to be concordant

Answer 5

0.2cm

Question 6

how can the concentration be calculated from a redox titration?

Answer 6

1 - write the ion-electron equation + combine to give the redox equation
write mole ratio
2 - calculate the number of moles of the known substance
write ‘real’ mole ratio
3 - calculate the concentration by c =moles/v

Question 7

what is chromatography?

Answer 7

a method of separating + analysing a mixture of soluble chemical substances

Question 8

what types of chromatography are there?

Answer 8

paper
thin layer
gas
gas liquid

Question 9

give the uses of chromatography??

Answer 9

to follow the course of a chemical reaction
to establish the products of a chemical reaction
identify additions in foods
analyse fibres found at a crime scene

Question 10

what is the main type of chromatography?

Answer 10

paper chromatography

Question 11

how is paper chromatography carried out?

Answer 11

small sample of mixture being tested is spotted onto the baseline on the filter paper
filter paper placed in solvent
by capillary action the solvent moves up paper; this is when different components of the mixture are separated

Question 12

what are the two stages in paper chromatography?

Answer 12

mobile phase; the solvent

stationary phase; wet paper

Question 13

why does separation in chromatography occur?

Answer 13

due to polarity + size of molecules within the mixture
polar molecules move much quicker up the filter paper due to being more attracted to the polar solvent of the mobile phase
smaller molecules move much quicker + further up the filter paper compared to larger molecules

Question 14

what are retention factor values used for?

Answer 14

to compare the different components in a sample
if 2 substances on chromatography paper have the same Rf value it is likely they are the same compound
if they don’t have the same Rf value they are different compounds

Question 15

give the Rf value equation

Answer 15

distance from the baseline to the spot/distance from the baseline to the solvent front

Question 16

how can the identity of a component be indicated?

Answer 16

by the distance it has traveled or the time it took to travel through the apparatus (retention time)

Question 17

what keywords should you use when analysing a chromatogram?

Answer 17

peaks, retention time, quantity, affinity, shortest/largest, least/most