T8 chemical analysis

Question 1

what is a pure substance

Answer 1

single element or compound, not mixed with any other substance

Question 2

what is a formulation and how is it made

give examples

Answer 2

• mixture of compounds in measured quantities that has been designed as a useful product
• formulations include fuels, cleaning agents, alloys, medicines, fertilisers
  e. g. alloys are mixtures of metals, harder than pure metals so have a particular purpose

Question 3

describe paper chromatography

Answer 3

1. start line is drawn near the bottom of the paper. Mixture is spotted on the line
2. beaker is filled with small amount of solvent
3. paper is hung on a rod and placed in a beaker
4. solvent travels up the paper, separating the components
5. before solvent level reaches the end, paper is taken out and the finish line is marked, paper is dried
6. procedure works when different compounds have different affinities for the solvent/paper. Stronger attraction for the paper - travels slowly with the solvent
7. paper is called the stationary phase - doesn’t move, solvent is the mobile phase

Question 4

how is Rf calculated

Answer 4

distance moved by the spot / distance moved by solvent

Question 5

describe the tests for hydrogen, oxygen, carbon dioxide and chlorine

Answer 5

H - pop with burning split over gas
O - glowing split relights
D - turns limewater (Ca(OH)2) milky
C - bleaches damp litmus paper and makes it white

Question 6

describe the flame test results

Answer 6

lithium compounds - crimson red flame
sodium compounds - yellow flame
potassium compounds - lilac flame
calcium compounds - orange red flame
copper compounds - green flame

Question 7

describe the test for carbonate anions

Answer 7

add dilute acid e.g. HCl

fizzing observed as CO2 released

Question 8

describe sulfate tests

Answer 8

add a solution containing Ba2+ cations

white precipitate pf BaSO4 forms

Question 9

describe silver nitrate tests

Answer 9

add a solution of AgNO3 (acidified with HNO3)
chlorines - white precipitate, silver chloride
bromides - cream precipitate, silver bromide
iodides - yellow precipitate, silver iodide

Question 10

what are instrumental methods

Answer 10

accurate, sensitive and rapid methods which are useful when the amount of sample is very small

Question 11

describe the flame emission spectroscopy

Answer 11

a) instrumental method used for identifying metal ions in solution or measuring their concentration
b) Spectroscope measures the exact wavelength of the light emitted by a metal ion

c) That allows for definite identification - sometimes colours are difficult to
distinguish.

d) Concentrations are found by measuring the intensity of light emitted. The more intense light, the greater the concentration of the metal ion in a solution.

e) From the intensity vs concentration graph, you can read off a relevant
concentration value at a given intensity.

Question 12

what are cations and anions

Answer 12

c - positive ions

a - negative ions

Question 13

describe the sodium hydroxide test results

Answer 13

copper (II) forms a blue precipitate

iron (II) forms a dirty green precipitate

iron (III) forms a brown precipitate

Al3+, Ca2+, Mg2+ forms white precipitate but only Al(OH)3 dissolves in excess NaOH to form a colourless solution

Question 14

in paper chromatography experiment, a compound A was found to have an Rf value of 0.85 - what does it tell you about the compound

Answer 14

has a higher affinity for the solvent than for the paper