topic 8 - chemical analysis

Question 1

whats a pure substance

Answer 1

only contains one compound or element (not mixed with anything else)

Question 2

how do you test for a pure substance with melting and boiling points

Answer 2

test its melting and boiling point and because pure substances have specific melting and boiling points, the closer it is to these, the more pure it is

Question 3

what are formulations

Answer 3

useful mixtures with a precise purpose made following a formula (recipe/method)

Question 4

examples of formulations

Answer 4

• paints
• medicines
• cleaning poruducts
• fertilisers

Question 5

mobile and stationary phase - chromatography

Answer 5

mobile - where molecules can move -> liquid/gas
stationary - molecules cant move -> solid/thick liquid

Question 6

what does a pure substance look like in chromotography

Answer 6

just one dot anywhere on the paper

Question 7

what are the phases in PAPER chromatography

Answer 7

• stationary - chromatography paper/filter paper
• mobile - solvent eg water/ethonol

Question 8

what spends more time in the mobile phase

Answer 8

molecules with a higher solubility which are less attracted to the paper

Question 9

formula for the Rf value

Answer 9

distance travelled by substance / distance travelled by solvent

Question 10

test for 4 common gasses: CHLORINE, OXYGEN, CO2, HYROGEN

Answer 10

1. chlorine - bleaches damp litmus paper white
2. oxygen - relight a glowing splint in a test tube
3. CO2 - bubbling it through limewater - goes cloudy
4. hydrogen - lit splint in test tube - squeaky pop

Question 11

name the 3 tests for ANIONS

Answer 11

• carbonates
• sulfates
• halides

Question 12

what is the test for carbonates (ANIONS 1)

Answer 12

add DILUTE ACID to test tube and connect to test tube of LIMEWATER - if positive - CO2 released making limewater cloudy

Question 13

what is the test for sulfates (ANIONS 2)

Answer 13

add drops of DILUTE HCL to sample with BARIUM CHLORIDE solution - if posiitve - white [precipitate forms

Question 14

what is the test for halides (ANIONS 3) and anogram

Answer 14

add drops of dilute nitric acid and silver nitrate:
- chloride - WHITE - silver chloride
- bromide - CREAM - silver bromide
- iodide - YELLOW - silver iodide

Question 15

whats the test for CATIONS 1

Answer 15

the flame test

Question 16

results of the flame test for CATIONS identifying metal ions

Answer 16

lithium - red
sodium - yellow
potassium - lilac
calcium - orange
copper - green

Lola
Rides
Stalions
Yawning
Penelope
Licks
Corolines
Ovaries
Copper
Green

Question 17

how do you carry out the test for CATIONS that gives you a precipitate (other than the flame test)

Answer 17

add few drops of SODIUM HYDROXIDE to mystery solution

Question 18

results of sodium hydroxide test with metal ions for CATIONS

Answer 18

calcium - white
copper (II) - blue
iron (II) - green
iron (III) - brown
aluminium - white then colourless
magnesium - white

Coroline
Wets
Charlies
Bread
In
Greece
Inigo
Buts
Away
Wailing
‘My
Wife’

Question 19

why is flame spectroscopy better than the flame test

Answer 19

• very sensitive - detects tiny amounts of light
• very fast - tests are automated
• very accurate

Question 20

explain flame emission spectroscopy

Answer 20

• a sample is placed in flame and as it heats the electrons become excited and transfer energy as light
• this light passes through a spectroscope which detects different wavelengths which produce a line spectrum
• this creates different patterns so we can identify what ions are in the solution
• and the intensity of the line can tell us the concentration of that ion in the solutions

Question 21

when would you need to use flame emission spectroscopy

Answer 21

• if 2 metals have similar colours
• sample may contain multiple metals so colours could get mixed up

Question 22

what does it mean in chormatography if your dot has reached the furthest

Answer 22

its the most soluable