8-Chemical Analysis

Question 1

What is purity defined as in chemistry

Answer 1

A pure substance only contains one compound or element and is not mixed with anything else

Question 2

How can u test the purity of a substance

Answer 2

Measure its melting or boiling point and compare it the melting or boiling point of the pure substance.
The closer it is to the actual m.p or b.p the pure pure it is

Question 3

What will impurities do to the melting point of the substance

Answer 3

It will lower the melting point and increase the melting range of the substance

Question 4

What will impurities do to the boiling point of a substance

Answer 4

They will increase the boiling point and it may result in the substance boiling at a range of temperatures

Question 5

What is a formulation

Answer 5

Useful mixtures with a precise purpose that are made by following a formula

Question 6

What are examples of formulations

Answer 6

Found in:
Cleaning products 
Fuels
Cosmetics
Fertilisers
Metal alloys
Food and drink

Question 7

What is the mobile phase

Answer 7

Where the molecules can move. This is always a liquid or a gas

Question 8

What is the stationary phase

Answer 8

Where the molecules can’t move.

This can be a solid or a really thick liquid

Question 9

What is the stationary phase in paper chromatography

Answer 9

The filter paper

Question 10

What is the mobile phase in paper chromatography

Answer 10

The solvent - water or ethanol

Question 11

What does the amount of time spent in each phase depend on

Answer 11

How soluble they are in the solvent,

How attracted they are to the paper

Question 12

What happens to molecules that have a higher solubility

Answer 12

They spend more time in the mobile phase and are carried further up the paper

Question 13

What is a chromatogram

Answer 13

The result of the chromatography analysis on the paper

Question 14

How do u calculate Rf value

Answer 14

Rf = distance travelled by substance(B) / distance travelled by solvent(A)

Question 15

How many spots will be on the chromatogram if the substance is pure

Answer 15

1

Question 16

What is the test for chlorine

Answer 16

It bleaches damp litmus paper white

Question 17

What is the test for oxygen

Answer 17

It will relight a glowing splint

Question 18

What is the test for carbon dioxide

Answer 18

Bubbling CO2 through an aqueous solution of calcium hydroxide (lime water) will turn it cloudy

Question 19

What is the test for hydrogen

Answer 19

If u hold a lit splint at the open end of a test tube containing hydrogen, you’ll get a squeaky pop

Question 20

How do u test for carbonates

Answer 20

Add dilute acid to the sample,
Connect test tube to some lime water,
If lime water goes cloudy then carbonate is present

Question 21

How do you test for sultates

Answer 21

Add a couple drops of dilute hydrochloric acid and a couple of drops of barium chloride solution to the sample.
If sulfate ions are present, a white precipitate is formed

Question 22

How do u test for Halides

Answer 22

Add a couple drops of dilute nitric acid and a couple drops of silver nitrate solution to the sample

Question 23

What do chloride, bromide and iodide produce in the halide test

Answer 23

Chloride- white precipitate of silver bromide
Bromide- cream precipitate of silver bromide
Iodide- yellow precipitate of silver iodide

Question 24

What colour flame do lithium ions produce

Answer 24

Crimson

Question 25

What colour flame do sodium ions produce

Answer 25

Yellow

Question 26

What colour flame do potassium ions produce

Answer 26

Lilac

Question 27

What colour flame do calcium ions produce

Answer 27

Orange-red

Question 28

What colour flame do copper ions produce

Answer 28

Green

Question 29

How do prepare for a flame test

Answer 29

Clean a platinum wire loop by dipping it some dilute HCL and then hold in blue flame until it burns without any colour

Question 30

How do u carry out a flame test

Answer 30

Dip titanium loop into sample and put it in the flame. | Record the colour of the flame

Question 31

How do u test for metals

Answer 31

Add a few drops of sodium hydroxide solution to the sample. | If metal present, it forms an insoluble hydroxide

Question 32

What colour precipitate does calcium produce when sodium hydroxide is added

Answer 32

White

Question 33

What colour precipitate does copper(II) produce when sodium hydroxide is added

Answer 33

Blue

Question 34

What colour precipitate does iron (II) produce when sodium hydroxide is added

Answer 34

Green

Question 35

What colour precipitate does iron(III) produce when sodium hydroxide is added

Answer 35

Brown

Question 36

What colour precipitate does aluminium produce when sodium hydroxide is added

Answer 36

White at first but then redissolves in excess NaOH to form a colourless solution

Question 37

What colour precipitate does magnesium produce when sodium hydroxide is added

Answer 37

White

Question 38

Explain how a coloured flame is produced

Answer 38

As the ions heat up, their electrons become excited. When the electrons drop back to their original energy levels, they transfer energy as light

Question 39

What is a spectroscope

Answer 39

As light passes through it, it can detect different wavelengths of light to produce a line spectrum

Question 40

What does the intensity of the spectrum show

Answer 40

Shows the concentration of that ion in the solution

Question 41

What are the advantages of instrumental analysis (tests that use machines)

Answer 41

Very sensitive Very fast Very accurate