Qualitative analysis- tests for ions

Question 1

What is an ion?

Answer 1

A charged atom, molecule or particle.

Question 2

Why must a test for a specific ion be unique?

Answer 2

Tests are used to identify ions and must
be unique so that the test gives an easily
observed result which is specific to the
ion that is present.

Question 3

Describe how you would carry out a flame test to test

for ions

Answer 3

• Clean a nichrome wire using hydrochloric acid.
• Turn the Bunsen burner onto the blue flame.
• Dip the wire in a solution of the substance being
  tested.
• Place the wire in the flame and record the
  colour

Question 4

What is the result of the flame test on lithium ions?

Answer 4

Crimson flame

Question 5

What is the result of the flame test on sodium ions?

Answer 5

Yellow flame

Question 6

What is the result of the flame test on potassium

ions?

Answer 6

Lilac flame

Question 7

What is the result of the flame test on calcium ions?

Answer 7

Orange flame

Question 8

What is the result of the flame test on copper ions?

Answer 8

Blue-green flame

Question 9

Why must the wire be cleaned before carrying out a

flame test?

Answer 9

To remove any unwanted ions that might

obscure the colour of the flame

Question 10

Why can a flame test not be used when a compound

contains a mixture of metal ions?

Answer 10

The flame colours of the ions will blend
together so the individual flame colours
won’t be seen meaning the ions can’t be
identified.

Question 11

What is a precipitate?

Answer 11

An insoluble solid suspended in a liquid.

Question 12

Without using the flame test, how can you test for

aqueous metal ions?

Answer 12

Add sodium hydroxide solution to the
metal ions. Observe the colour of the
precipitate.

Question 13

What colour precipitate forms when sodium

hydroxide reacts with calcium ions?

Answer 13

White

Question 14

What colour precipitate forms when sodium

hydroxide reacts with copper(II) ions?

Answer 14

Blue

Question 15

What colour precipitate forms when sodium

hydroxide reacts with iron(II) ions?

Answer 15

Green

Question 16

What colour precipitate forms when sodium

hydroxide reacts with iron(III) ions?

Answer 16

Brown

Question 17

What colour precipitate forms when sodium

hydroxide reacts with aluminium ions?

Answer 17

White (initially)

With excess NaOH, the precipitate
re-dissolves to form a colourless solution.

Question 18

What is observed when sodium hydroxide reacts

with ammonium ions?

Answer 18

A pungent smelling gas is produced
(NH3) which will turn damp red litmus
paper blue.

Question 19

How could you distinguish between two solutions

containing aluminium ions and calcium ions?

Answer 19

Add excess sodium hydroxide.

Both will form white precipitates initially. The
precipitate formed from aluminium ions will
re-dissolve to form a colourless solution.

Question 20

How can you test for carbonate ions?

Answer 20

• Add a few drops of HCl to the sample in a test tube.
• Connect this test tube to a test tube of limewater.
• If carbonate ions are present, they will react with the
  acid to produce carbon dioxide which will turn the
  limewater cloudy when it is bubbled through
  limewater.

Question 21

Write the chemical equation for the reaction between

HCl and Na2CO3

Answer 21

Na2CO3 + 2HCl → CO2 + 2NaCl + H2O (check google if unsure)

Question 22

How can you test for sulfate ions?

Answer 22

- Add HCl to remove any CO3 ^2-
ions as these will obscure the results.
- Add a couple of drops of barium chloride.
- If sulfate ions are present a white
precipitate of barium sulfate will form.

Question 23

Write the chemical equation for the reaction between
BaCl2
and MgSO4

Answer 23

BaCl2 + MgSO4 → BaSO4 + MgCl2

BaSO4 is a white precipitate

(check google if unsure)

Question 24

How do you carry out a test for halide ions?

Answer 24

• Add a few drops of nitric acid to react with
  any carbonate ions which might obscure
  the result.
• Add a couple of drops of silver nitrate.
• Observe the colour of the precipitate.

Question 25

What colour precipitate is formed when silver nitrate

is added to a chloride solution?

Answer 25

White precipitate of silver chloride

Question 26

What colour precipitate is formed when silver nitrate

is added to a bromide solution?

Answer 26

Cream precipitate of silver bromide

Question 27

What colour precipitate is formed when silver nitrate

is added to an iodide solution?

Answer 27

Yellow precipitate of silver iodide

Question 28

What is meant by the phrase instrumental methods
of analysis? Give an example of an instrumental
method used for the analysis of elements or
compounds

Answer 28

Methods of analysis that use machinery
such as mass spectrometry and gas
chromatography.

Question 29

What are the benefits of using instrumental methods

for analysis?

Answer 29

• Accurate
• Sensitive
• Quick to carry out

Question 30

What is a flame photometer?

Answer 30

A device used in inorganic analysis. It

can be used to identify or determine the concentration of metal ions.

Question 31

How can a flame photometry be used to identify metal ions?

Answer 31

An emission spectrum is produced by
the flame photometer. Each metal ion
produces a unique spectrum so
comparing the unknown spectrum to
reference spectra can identify the ion

Question 32

How can a flame photometry be used to determine

the concentration of metal ions?

Answer 32

Take readings using a flame photometer of the metal ions at different concentrations. Plot a calibration curve. Take a reading of the unknown sample and compare to the curve.

Question 33

What is the major advantage of flame photometry compared to simple flame testing?

Answer 33

Flame photometry can be used to analyse a mixture of ions whereas flame tests can only be used to identify one ion at a time.

Question 34

ROYGBIV =__________

Answer 34

LiCaNaCuK

R=Li
O=Ca
Y=Na
GB=Cu
IV=K