C12: Chemical Analysis

Question 1

what is a pure substance?

Answer 1

single element or compound, not mixed with any other substance

Question 2

how do you know its a pure substance?

Answer 2

melt/boil at specific temps
- mixtures have range of MPs and BPs

Question 3

what is a formulation?

Answer 3

mixture that has been desiged as a useful product
- made my mixing components in carefully measured quanities to ensure product has required properties

Question 4

examples of formulations ?

Answer 4

fuels, cleaning agents , paints amnd medecines

Question 5

process of chromotography?

Answer 5

• pencil line drawn on chromotography paper/ spots of sample placed on it
• paper lowered into solvent , making sure pencil line is above solvent
• different substance have differnt solubility so travel at different rates (high solubility-travel further)

Question 6

how can u identify if substance is pure or not from chomotography?

Answer 6

pure substance only has one spot on chromotogram
- mixtures have multiple

Question 7

how to calculate Rf value?

Answer 7

distance moved by substance/distance moved by solvent

Question 8

flame test for

Lithium?

Answer 8

crimson

Question 9

flame test for

sodium

Answer 9

yellow

Question 10

flame test for

potassium

Answer 10

lilac

Question 11

flame test for

calcium

Answer 11

orange-red

Question 12

flame test for

copper

Answer 12

green

Question 13

effect of adding metal NaOH to

aluminium. calcium, magnesium

Answer 13

white precipitate
(only aluminium’s precipitate dissolves when excess NaOh is added)

Question 14

effect of adding metal NaOH to

copper

Answer 14

blue precipitate

Question 15

effect of adding metal NaOH to

iron II/iron III

Answer 15

iron II - green precipitate
iron III - brown precipitate

Question 16

test for carbonates?

Answer 16

carbonates will react with dilute acids - create CO2
- gas can be bubbled through limewater to test for CO2

Question 17

test for halides and results?

cats with brains can ideally yodel

Answer 17

• add dilute nitric acid and silver nitrate solution
  CHLORIDE - white precipitate
  BROMIDE - Cream precipitate
  IODINE - yellow precipitate

Question 18

test for sulfates?

Answer 18

first add dilute Hcl , followed by barium chloride solution
- if sulfate ions are present, white pecipitate forms

Question 19

what do instrumental methods do and advantages?

Answer 19

detect/identify elements and compounds
- accurate
- sensitive/rapid

Question 20

what is flame emission spectroscopy?

Answer 20

instrumental method to analyse metal ions in solutions
- sample put into flame / light given out (due to electrons fallng back to energy levels) is passed through spectroscope
- results in line spectrum that can be analysed to identify metal ions/measure concentrations

Question 21

test for hydrogen, oxygen and chlorine?

Answer 21

HYDROGEN : burning splint held at open end of test tube of gas , pops
OXYGEN : glowing splint inserted into test tube of gas
- splint relights - O2

CHLORINE : damp litmus paper bleaches /turns white if present

Question 22

describe the the design and general properties of a formulation?

4mks

Answer 22

formulations are mixture designed to be useful products.
- measured quantities of components used
- each component has purpose
- giving mixture desired properties

Question 23

how does chromotography seperate dyes?

Answer 23

• solvent moves through paper
• different dyes have different solublities in solvent
• and different attrcations for the paper
• so carried different distances