Analysis + gases in the atmosphere Flashcards
(58 cards)
1
Q
What are the three steps to identify positive ions in substances?
A
- flame test
- add sodium hydroxide
- to produce precipitate
- warm solution in hot water baths and test gas produced with damp litmus paper
2
Q
Describe how to carry out a flame test
A
- clean a platinum wire by dipping it into concentrated acid to remove any impurities thta may change colour of flame
- then dip wire into solid being tested and hold it above a blue Bunsen flame until a recognisable colour change is visible
3
Q
Why is platinum wire used?
A
- inert (unreactive) and so doesn’t colour the flame
- high melting point so can withstand heat from blue flame
4
Q
Lithium flame test
A
Red
5
Q
Sodium flame test
A
Yellow
6
Q
Postassium flame test
A
Lilac
7
Q
Calcium flame test
A
Orange-red
8
Q
Copper(II) flame test
A
Blue-green
9
Q
Name the four ways to collect gases
A
- gas syringe
- over water
- upward delivery
- downward delivery
10
Q
What can we use gas syringe method for?
A
- any gas
- most accurate measuring
11
Q
What can we use over water method for?
A
- only works for gasses that are not soluble in water as they’d bubble through it and collect at top
- works for gases in similar density to air
12
Q
What can we use the upward delivery method for?
A
- gases thta are less dense than air so they would rise over it can collect at top
- solubility in water is irrelevant
13
Q
What can we use downward delivery for?
A
- gasses that are more dense than air air as they would sink beneath it
- solubility is irrelevant
14
Q
Hydrogen density compared to air and solubility in water
A
- less dense than air
- insoluble in water
15
Q
Oxygen density compared to air and solubility in water
A
- equal density to air
- insoluble in water
16
Q
CO2 density compared to air and solubility in water
A
- more dense than air
- insoluble in water
17
Q
Chlorine density compared to air and solubility in water
A
- more dense than air
- soluble in water
18
Q
Ammonia density compared to air and solubility in water
A
- less dense than air
- soluble in water
19
Q
Test for chlorine gas
A
- damp red litmus paper
- positive result = litmus paper bleaches
20
Q
Test for ammonia
A
- damp red litmus paper
- positive result = red litmus paper tunes blue (gas was alkaline)
21
Q
Test for hydrogen
A
- lit splint in tube of hydrogen
- squeaky pop will be heard
22
Q
CO2 test
A
- bubble through limewater
- positive result = limewater turns cloudy
23
Q
Test for oxygen
A
- use a glowing splint into tube if oxygen
- positive result = splint will relight
24
Q
Test for presence of water
A
- anhydrous white copper(II) sulfate
- turns from white to blue
25
Test for purity of water
- heat water and measure boiling point
- positive result = pure water boils at 100 degrees C
26
Test for copper(II) ions
- add sodium hydroxide to copper(II) sulfate
- positive result = clear blue solution becomes a cloudy blue one ( blue precipitate forms)
27
test for iron(II)
- add sodium hydroxide to iron(II) sulfate
- positive result = colourless solution. becomes green due to formation of green precipitate
28
Test for Iron(III)
- add sodium hydroxide to iron (III) sulfate
- positive result. = yellow solution to red-brown precipitate forms
29
Test for ammonia
- add sodium hydroxide to ammonium chloride
- put test tube containing this into hot water bath
- positive result = gas evolved turned red damp litmus paper blue a
30
Why must litmus paper be damp when testing for ammonia?
acids and alkalis only react when dissolved in water
31
Test for sulfates using sodium sulfate
- add sodium sulfate to a test tube and then add some hydrochloric acid and barium chloride
- positive result = white precipitate forms
32
Why do we add acid to a sulfate solution?
To prevent the formation of other precipitates as the acid will react with any carbonates present
33
Test for sulfates using copper(II) sulfate
- take a test tube and add sopper(II) sulfate and add hydrochloric acid and barium chloride
- positive result = white precipitate forms
34
Test for carbonate ions using calcium carbonate
- add calcium carbonate to hydrochloric acid
- then collect gas using downward delivery
- bubble gas through limewater
- positive result = limewater turns cloudy
35
Test for carbonate ions using sodium carbonate
- add hydrochloric to sodium carbonate
- collect gas produced using downward delivery
- bubble gas produced through limewater
- positive result = gas produced turns limewater cloudy
36
Percentages of gasses in the air
- nitrogen = 78%
- oxygen = 21%
- carbon dioxide = 0.04%
- argon and other gasses = less than 1%
37
Why must the solution to test for halides be acidified?
prevent the formation of other precipitates
38
Test for chloride ions
- to a test tube containing 2cm cubed water, add some potassium chloride and nitric acid, then a few drops of silver nitrate to prevent formation of other precipitates
- positive result = white precipitate forms
39
Test for bromide ions
- to a test tube containing 2cm cubed water, add some potassium bromide and nitric acid, then a few drops of silver nitrate to prevent formation of other precipitates
- positive result = cream coloured precipitate forms
40
Test for iodide ions
- to a test tube containing 2cm cubed water, add some potassium iodide and nitric acid, then a few drops of silver nitrate to prevent formation of other precipitates
- positive result = yellow precipitate formed
41
name the four most abundant gases in dry, unpolluted air
- nitrogen = 78%
- oxygen = 21%
- argon = <1%
- CO2 = 0.04%
42
describe how to find the % of oxygen in the air - copper(II) oxide method
- fill the gas syringe with 100cm3 air, with copper in between the syringes
- heat the copper strongly using a roaring bunsen flame
- pass air over the copper
- eventually pink-brown copper will become black copper(II) oxide, and the volume of air in the syringe will decrease
- continue passing air over the copper(II) oxide until there is no longer a change in volume
43
describe how to calculate the % of oxygen in the air using the results of the copper(II) oxide experiment
- change in volume = initial (100cm3) - final(79cm3) = 21cm3
- percentage change = % O2 in air = 21/100 x 100 = 21%
44
symbol equation of reaction of copper with oxygen
2Cu (s) + O2 (g) => 2CuO (s)
45
describe how to find the % of oxygen in the air - rusting of iron method
- push a piece of iron wool through the bottom of the burette so approx 3 cm is inside
- fill a plastic trough with a few centimeters of water
- add water to the burette, then invert it into the trough to prevent water from escaping - exact volume doesn’t matter as long as the initial reading can be recorded
- note the initial volume of water inside the burette
- leave the apparatus undisturbed in the lab for at least a week to allow rusting to occur
- after a week, record the final volume of water in the burette
46
describe how to calculate the % of oxygen in the air using the results of the iron rusting experiment
% of O2 in air = change in height of water in burette / initial volume of air in burette
47
describe how to find the % of oxygen in the air - phosphorus method
- phosphorus is placed in an evaporating basin in a water trough covered by a sealed bell jar
- phosphorus is ignited by a hot metal rod
- white phosphorous oxide gas is produced as the phosphorus burns and uses up the oxygen in the air
- water level rises to replace oxygen in the air
- white smoke dissolves into water
- when water level stops rising it is marked
48
describe how to calculate the % of oxygen in the air using the results of the phosphorus experiment
% of O2 in air = water level of bell jar = approx 20%
49
describe the combustion of magnesium in oxygen
- burns with a bright white flame
- silver magnesium becomes white magnesium oxide powder
- 2Mg (s) + O2 => 2MgO (s)
50
describe the combustion of sulfur in oxygen
- burns with a blue flame
- poisonous, colourless sulfur dioxide gas is produced
- S (s) + O2 (g) => SO2 (g)
51
describe the combustion of hydrogen in oxygen
- burns with a pale blue flame
- produces water
- a squeaky pop is heard
- 2H2 (g) + O2 (g) => 2H2O (l)
52
define thermal decomposition
a reaction where heat causes a compound to break down into its simpler components
53
what do metal carbonates thermally decompose into?
metal oxide and carbon dioxide
54
describe the thermal decomposition of copper(II) carbonate
- green copper(II) carbonate powder becomes a black powder of copper(II) oxide
- carbon dioxide gas is given off
- CuCO3 (s) => CuO (s) + CO2 (g)
55
what gas is produced in the thermal decomposition of metal carbonates and how can we test it?
- carbon dioxide gas is produced in the thermal decomposition of metal carbonates
- the gas can be tested by bubbling it through limewater to see if it turns cloudy
56
what type of gas is carbon dioxide?
greenhouse gas
57
what is a greenhouse gas?
a gas in the earth's atmosphere that traps heat, contributing to the greenhouse effect and global warming
58
Word and symbol equation for formation of rust
- symbol = 4Fe (s) + 3O2 (g) -> 2Fe2O3 (s)
- word = iron + oxygen -(in presence of water)—> hydrated iron(III) oxide
