Topic 8 - Chemical Analysis

Question 1

How can you test the purity of a substance?

Answer 1

By measuring the melting point and comparing it to the specific value for that substance in a data book - the closer the value is the purer the substance

Question 2

What is a formulation?

Answer 2

Formulations are mixtures that have been designed as a useful product

Question 3

What is the mobile and stationary phase in paper chromatography?

Answer 3

The mobile phase is where molecules can move so it is the solvent, the stationary phase is where molecules can’t move so it is the paper

Question 4

What is the Rf value formula

Answer 4

Rf = distance travelled by substance ÷ distance travelled by solvent

Question 5

What is the test for carbon dioxide?

Answer 5

bubbling (or shaking) carbon dioxide through an aqeous solution of calcium hydroxide (limewater) causing the solution to turn cloudy if carbon dioxide is present

Question 6

What is the method for flame tests?

Answer 6

First put on lab coat and goggles. Then clean a nichrome wire by rubbing it with emery paper and then heating it in the blue flame. Once clean dip loop into sample and put it back into blue flame and record colour

Question 7

What is the flame test results for - lithium, sodium, potassium, calcium and copper

Answer 7

lithium - crimson, sodium - yellow, potassium - lilac, calcium - orange/red, copper - green

Question 8

What is a limitation to the flame test?

Answer 8

A sample containing a mixture may mean that a flame colour can be masked by another

Question 9

What is the method for metal hydroxide test?

Answer 9

add a few drops of sodium hydroxide solution and note the coloured precipitate

Question 10

What are the hydroxide test results for calcium, copper(II), iron(II), iron(III), aluminium, magnesium?

Answer 10

calcium - white precipitate, copper(II) - blue precipitate, iron(II) - green precipitate, iron(III) - brown precipitate, aluminium - white precipitate (dissolves with more solution), magnesium - white precipitate

Question 11

Describe the test and results for halides?

Answer 11

add a couple drops of dilute nitric acid followed by a couple drops of silver nitrate solution - chlorine is white precipitate, bromine is cream precipitate and iodine is yellow precipitate

Question 12

Describe test and results for carbonate test?

Answer 12

add few drops of dilute acid to form carbon dioxide and then do the limewater test so if it is present the limewater should turn cloudy

Question 13

Describe test and results for sulfate test?

Answer 13

add couple drops of dilute hydrochloric acid followed by a couple drops of barium chloride solution - if sulfate ion are present then a white precipitate will form

Question 14

Advantages and disadvantages of instrumental methods?

Answer 14

Advantages - accurate, sensitive, quick / Disadvantages - very expensive

Question 15

What is an instrumental method of analysing metal ions in solution

Answer 15

flame emission spectroscopy

Question 16

How does flame emission spectroscopy work?

Answer 16

as ions in the sample heat, up the electrons move to higher energy levels, when they return to original levels they release light energy, a spectroscope detects different wavelengths and produces a line spectrum