Chemical Analysis

Question 1

Purity

Answer 1

contains only 1 element/compound

Question 2

How to identify a pure substance?

Answer 2

melting/boiling points - tehy have specific temperature

Question 3

Test for purity

Answer 3

Comparing boiling/melting point of sample and pure substance. The smaller difference in melting/boiling points, the purer the substance is.

Question 4

The more impurities…

Answer 4

Lower melting/higher boiling points + increased difference in melting/boiling points between pure substance and sample

Question 5

Formulation

Answer 5

Useful mixtures with precise purpose + made following a recipe where every component is a measured quantity and contributes for the properties to meet their require function

Question 6

What is formulation used for?

Answer 6

Used in medicine (Pharmacy) - ensure drugs are delivered to right part of body at right concentration + is consumable and has a long enough shelf life

Question 7

How to check ingredients in a package?

Answer 7

Ratio/percentage on packaging of product

Question 8

Paper Chromatography

Answer 8

method to separate substances in mixture + identify substances

Question 9

2 phases

Answer 9

Mobile phase - where molecules can move (solvent)

Stationary phase - where molecules can’t move (paper)

Question 10

How does solvent move?

Answer 10

Substances constantly move between stationary and mobile phase and anything dissolved in mobile phase moves with it. How quickly chemical moves depends on how its”distributed” between 2 phases + whether more time spent in mobile/stationary phase

Question 11

What determines how much solvent moves up?

Answer 11

Chemicals that spend more time in mobile phase than stationary will move further up the stationary phase.

Question 12

How is the chemicals separated?

Answer 12

Components in mixture usually separate in stationary phase, only if component spend various amounts in mobile phase. N.o of spots change in difference solvents as distribution of chemical will change depending on solvent.

Question 13

What result would a pure substance give in a parer chromatography?

Answer 13

1 spot i any solvent as 1 compound/element

Question 14

Tests for common gases?

Answer 14

Chlorine - bleach damp litmus paper + turns white
Oxygen - glowing splint inside the test tube +splint relights
hydrogen - lit splint at tend of t test tube and hear a “squeaky pop”
C02 - bubble CO2 through an aqueous solution of limewater + it turns cloudy

Question 15

Dilute acid detecting carbonate

Answer 15

Put mystery solution in test tube +use dropping pipette to add couple of drops of dilute acid. Connect to test tube of mystery solution to test tube of limewater + CO2 will be released, turning limewater cloudy, if carbonate ions are present. Na2CO3 + 2HCL - CO2 +2NaCl+H20

Question 16

HCL =barium chloride detecting sulphates

Answer 16

Use dropping pipette to add few drops of dilute HCL followed by few drops of barium chloride solution to test tube of mystery solution. If sulphate ions are present, white precipitate of barium chloride should be present. Ba2+ +S02-4 -BaSO4

Question 17

Nitric acid +silver nitrate detecting halides

Answer 17

Add few drops of dilute nitric acid and few drops of silver nitrate to mystery solution.
Chloride gives white precipitate of silver chloride (Ag+ + Cl- - AgCl)
Bromide gives a cream/silver precipitate of silver bromide (Ag+ + Br- - AgBr)
Iodine gives a yellow precipitate of silver iodine (Ag+ + -I - AgI)

Question 18

Flame test method

Answer 18

Clean platinum wire loop by dipping dilute HCL + holding in blue flame of Bunsen Burner until it burns without colour. Dip loop in sample and put in flame. Record colour of flame.

Question 19

Colours of the flame tests

Answer 19

Sodium - yellow flame
Lithium - Crimson flame
Potassium - Lilac flame
Calcium (Ca2+) - orange/ red flame
Copper (Cu2+) - green flame

Question 20

Why are flame tests not the best method?

Answer 20

Can only test for 1 metal ion as colour of certain ions may be hidden colour of others or overlap and can be hard to distinguish colours of flames (similar colours0

Question 21

Flame Emission Spectroscopy

Answer 21

A sample is placed in a flame and the ions heat up, their electrons become excited. After the electrons drops to original energy level, they transfer energy. the light passes through a spectroscope to produce a line spectrums from the wavelengths of light emitted.

Question 22

How is each line spectrum different to each ion?

Answer 22

Each ion produces a specific combination of wavelengths according the charge or electron arrangement.

Question 23

What does line spectrum show?

Answer 23

The ion and their concentration

Question 24

Instrumental analysis - what is it and its advantages

Answer 24

using machines + it is very sensitive (detect tiniest amount of a substance), very fast and very accurate

Question 25

Why is dilute nitric acid added before silver nitrate ?

Answer 25

To detect any carbonate ions as carbonate ions will react with silver nitrate to make silver carbonate, creating a different precipitate and changes results.

Question 26

Why should the base/solvent lien be drawn in pencil?

Answer 26

Dye can diffuse into solvent instead of paper and dyes mix together and cant't be separated or dye can leak into other sample

Question 27

Metal Hydroxide Results

Answer 27

``` Calcium(Ca2+) - white Copper (Cu2+) - Blue IronII (FE2+) - green Iron III(Fe3+) - Brown Aluminium (Al3+) - white first, dissolves in excess NaOH= colourless solution Magnesium (Mg2+) - White ```