Chemical Analysis (8)

Question 1

What is a pure substance?

Answer 1

A pure substance is a single element or compound, not mixed with any other
substance

Question 2

What is a formulation and how is it made?

Answer 2

A formulation is a mixture of compounds in measured quantities that has been
designed as a useful product.

Question 3

What is an example of formulations

Answer 3

Formulations include fuels, cleaning agents, paints, medicines, alloys,
fertilisers and foods.

E.g. alloys are mixtures of metals; they are harder than pure metals, so have
a particular purpose.

Question 4

Describe paper chromatography in steps
(1)

Answer 4

A start line is drawn near the bottom of the paper. The mixture is spotted on the line.

Question 5

Describe paper chromatography in steps
(2)

Answer 5

A beaker is filled with small amount of solvent (it cannot touch or go above the start line
when paper is placed in a beaker)

Question 6

Describe paper chromatography in steps
(3)

Answer 6

Paper is hung on a rod and placed in a beaker.

Question 7

Describe paper chromatography in steps
(4)

Answer 7

Solvent travels up the paper, thus separating the components.

Question 8

Describe paper chromatography in steps
(4)

Answer 8

Before solvent level reaches the end, the paper is taken out and the finish line is
marked. The paper is dried.

Question 9

Describe paper chromatography in steps
(5)

Answer 9

The procedure works when different compounds have different affinities for the
solvent/paper. Stronger attraction for the paper - travels slowly with the solvent etc.

Question 10

Describe paper chromatography in steps
(6)

Answer 10

Paper is called the stationary phase - it doesn’t move. Solvent is the mobile phase.

Question 11

How is R(small f)calculated?

Answer 11

Distance moved by the spot / distance moved by solvent

Question 12

In a 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 12

It has a higher affinity for the solvent than for the paper.

Question 13

Describe the tests for hydrogen

Answer 13

Hydrogen – pop with burning splint over gas

Question 14

Describe the tests for oxygen

Answer 14

Oxygen – glowing splint relights

Question 15

Describe the tests for carbon dioxide

Answer 15

Carbon dioxide – turns limewater (Ca(OH)2) milky

Question 16

Describe the tests for chlorine

Answer 16

Chlorine – bleaches damp litmus paper and makes it white

Question 17

Describe the flame test results

Answer 17

Lithium compounds– crimson red flame

Question 18

Describe the flame test results

Answer 18

Sodium compounds - yellow flame

Question 19

Describe the flame test results

Answer 19

Potassium compounds - lilac flame

Question 20

Describe the flame test results

Answer 20

Calcium compounds – orange red flame

Question 21

Describe the flame test results

Answer 21

Copper compounds -green flame.

Question 22

Describe the sodium hydroxide test results and write the equations

Answer 22

Question 23

Describe the test for carbonate anions

Answer 23

Question 24

Describe the test for sulfate anions

Answer 24

Question 25

Describe the test for halide anions

Answer 25

Question 26

What are instrumental methods?

Answer 26

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

Question 27

Describe the flame emission spectroscopy Step 1

Answer 27

instrumental method used for identifying metal ions in solution or measuring their concentration

Question 28

Describe the flame emission spectroscopy (Step 2)

Answer 28

Spectroscope measures the exact wavelength of the light emitted by a metal ion

Question 29

Describe the flame emission spectroscopy (Step 3)

Answer 29

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

Question 30

Describe the flame emission spectroscopy (Step4)

Answer 30

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.

Question 31

Describe the flame emission spectroscopy (Step 5)

Answer 31

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

Question 32

What are cations and anions?

Answer 32

Cations are the positive ions; anions are the negative ions.