C4.2 Identifying the products of chemical reactions

Question 1

What are positive ions called?

Answer 1

Cations

Question 2

What are negative ions called?

Answer 2

anions

Question 3

What tests are used to identify positive ions ?

Answer 3

• The flame test
• Sodium hydroxide precipitate

Question 4

What tests are used to identify negative ions ?

Answer 4

• Testing for halide ions
• Testing for sulphate ions
• Testing for carbonate ions

Question 5

What is the method of the flame test?

Answer 5

• Dip a nichrome wire in hydrochloric acid to clean it
• Dip the clean wire into the sample
• Place the wire into the blue bunsen flame and note the colour

Question 6

Why is a nichrome wire used in the flame test?

Answer 6

A nichrome wire is used because its very unreactive and has a high melting point

Question 7

In the flame test, what colour flag appears when Lithium is present ?

Answer 7

Red

Question 8

In the flame test, what colour flag appears when Sodium is present ?

Answer 8

Yellow - Orange

Question 9

In the flame test, what colour flag appears when Potassium is present ?

Answer 9

Lilac

Question 10

In the flame test, what colour flag appears when Calcium is present ?

Answer 10

Red - orange

Question 11

In the flame test, what colour flag appears when Copper is present ?

Answer 11

Green - Blue

Question 12

What is the method of the Sodium Hydroxide precipitate test?

Answer 12

• Adding a few drops of sodium hydroxide so the solution we are testing
• Nothing the colour of any precipitate that forms
• Adding an excess of sodium hydroxide
• Noting whether the precipitate re-desolves

Question 13

What is the colour of the precipitate when calcium is present ?

Answer 13

White

Question 14

What is the colour of the precipitate when Zinc is present ?

Answer 14

White

Question 15

What is the colour of the precipitate when Iron ( Fe2+ ) is present ?

Answer 15

Green

Question 16

What is the colour of the precipitate when Iron ( Fe3+ ) is present ?

Answer 16

Brown

Question 17

What is the colour of the precipitate when Copper is present ?

Answer 17

Blue

Question 18

What’s a precipitate ?

Answer 18

An insoluble solid

Question 19

What are the reactions called from sodium hydroxide precipitate test?

Answer 19

Precipitation reactions

Question 20

How are we able to distinguish Zinc or Calcium in the sodium hydroxide precipitate test ?

Answer 20

Out of the two, Zinc is the only one that desolves with excess NaOH ( Sodium hydroxide )

Question 21

What metal ion desolves with excess NaOH ( Sodium hydroxide ) ?

Answer 21

Zinc

Question 22

What is the method for the test for Sulphate ions ?

Answer 22

• Add 2 drops HCl (aq) ( hydrochloric acid ) - it removes any carbonate ions which would also give a white precipitate
• Add 2 drops BaCl2 ( aq )

Question 23

What is the equation for testing for Sulphate ions?

Answer 23

Ba^2+ (aq) + SOv4^2- (aq) => BaSOv4 (s).

Question 24

What is the method for the test for Carbonate ions ?

Answer 24

• Add acid [ eg. HCl (aq ) ]
• Bubble any gas produced through lime water
• If lime water goes cloudy means carbonate ions are personal

Question 25

What is the equation for testing for Carbonate ions?

Answer 25

2H^+ (aq) + COv3^2- (aq) --> Hv2O (l) + COv2 (g)

Question 26

What are the results of testing for carbonate ?

Answer 26

Results : Observe fizzing because COv2 produced ( limewater turns cloudy )

Question 27

What is the method for the test for halide ions ?

Answer 27

- Add 2 drop of HNOv3 [ dilute nitric acid ] - removes any carbonate ions, which would also give a white precipitate - Add 2 drops AgNOv3 (aq) [ silver nitrate solution ]

Question 28

What colour precipitate comes out from silver nitrate + chlorine , bromine , iodine ion ?

Answer 28

chlorine --> forms white ppt Bromine --> forms cream ppt Iodine --> Forms yellow ppt

Question 29

What colour precipitate comes out from Barium chloride + sulphate ions ?

Answer 29

White precipitate

Question 30

How does instrumental analysis compare to other tests?

Answer 30

- Its more accurate - Its faster ( and run all the time ) - Its more sensitive ( can use very small samples )

Question 31

How does infrared spectroscopy work ?

Answer 31

Infrared radiation is passed through a sample. Different types of covalent bond absorb different frequencies of infrared, which images the bonds vibrate. The resultant spectrum shows "peaks" which so respond to different types of covalent bonds

Question 32

What does a mass spectrum show?

Answer 32

- The peak with the highest mass to charge ratio is called the molecular ion peak - The mass to change ratio ( m/z ) of this peak tells us the relative mass ( Mr ) or the molecule

Question 33

What is gas chromatography ?

Answer 33

An instrumental technique that separates mixtures in the gas state

Question 34

How does gas chromatography work?

Answer 34

- The mixture enters the column as a gas and is carried along the carrier gas - Components that don't bond to the silica powder have a short retention time and reach the end of the column quickly - Components that bond to the silica powder take a long time to come out ( have a long retention time ) - At the end of the column is a detector, that makes a graph called a gas chromatogram

Question 35

What is the mobile phase in gas chromatography ?

Answer 35

An unreactive carrier gas ( like nitrogen or helium )

Question 36

What is the stationary phase in gas chromatography ?

Answer 36

Silica ( or alumina ) powder packed in a metal column

Question 37

What does this gas chromatogram show ?

Answer 37

- 3 peaks = 3 substances in the mixture - the furthest peak to the right has the longest retention time - the second peak (B) is the tallest peak so there is more substance B

Question 38

How to test for Hydrogen ?

Answer 38

A lighted splint will produce a squeaky pop in precense of hydrogen

Question 39

How to test for Oxygen ?

Answer 39

A glowing splint reignites the precedes of oxygen

Question 40

How to test for CO2 ?