C12 Chemical Analysis

Question 1

positive test for hydrogen

Answer 1

lighted splint into test tube ‘pops’

Question 2

positive test for oxygen

Answer 2

glowing splint relights

Question 3

positive test for carbon dioxide

Answer 3

turns limewater cloudy

Question 4

positive test for chlorine

Answer 4

turns damp blue litmus paper white

Question 5

positive test for water

Answer 5

cobalt chloride paper changes from blue to pink
or
white anhydrous copper sulfate changes from white to blue

Question 6

what are flame tests for?

Answer 6

to identify the metal ion (cation) by the colour of its flame.

Question 7

flame colour tests

Answer 7

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

Question 8

describe the steps of a flame test

Answer 8

• dip into hydrochloric acid and high temperature to clean the loop,
• dip loop into metal compound being tested,
• hold it in blue flames,
• use the colour the flames turn to to identify what is the metal compound

Question 8

describe the steps of a flame test

Answer 8

• dip into hydrochloric acid and high temperature to clean the loop,
• dip loop into metal compound being tested,
• hold it in blue flames,
• use the colour the flames turn to to identify what is the metal compound

Question 9

ions that form white precipitates with sodium hydroxide solution

Answer 9

calcium
and magnesium ions

Question 10

which metal ions form which-coloured precipitates in sodium hydroxide solution

Answer 10

copper II ions form blue precipitate
iron II ions form green precipitate
iron III ions form brown

Question 11

3 negative ions you can perform chemical tests for

Answer 11

sulfates
carbonates
halides (group 7)

Question 12

how to test for carbonates

Answer 12

add dilute acid: if it produces carbon dioxide effervescence (checked with limewater), it is a carbonate

Question 13

how to test for halides

Answer 13

1. add dilute nitric acid,
2. add silver nitrate solution,
3. if precipitate forms, halide ions are present and can be identified by the colour of the precipitate.

Question 14

precipitate colours for halide ions when added to dilute nitric acid and silver nitrate solution

Answer 14

iodide: yellow
bromide: cream
chloride: white

Question 15

how to test for sulfate ions

Answer 15

add dilute hydrochloric acid and barium chloride solution,
white precipitate means sulfate ions are present.

Question 16

what are the advantages and disadvantages of instrumental methods of chemical analysis?

Answer 16

advantages
- very accurate and sensitive,
- quicker,
- very small samples can be analysed,

disadvantages
- expensive,
- require special training,
- data can often only be interpreted in comparison to other data *complex and difficult to interpret)

Question 17

which ions does flame emission spectroscopy identify and how?

Answer 17

identifies metal ions
by heating a metal substance
and matching the wavelengths of light that it emits to the wavelengths of light emitted by specific metal ions.

Question 18

main advantage of flame emission spectroscopy

Answer 18

you can more easily identify multiple metal ions in one substance by matching up the emitted wavelengths to those of many metal ions,
unlike flame tests which - when mixed with many colours - rely on visual estimation