Analysis + gases in the atmosphere Flashcards
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 diffing it into concentrated acid to remove any impurities thta may change colour of flame
- then dip wire into solid being testes and hold it above à 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 air as
- 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 air as
- 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
- positive result = turned red damp litmus paper blue
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 cabr8nate to hydrochloric acid
- then collect gas using downward delivery
- bubble gas through limewater
35
Test for carbonate ions using sodium carbonate
- add hydrochloric to sodium carbonate
- collect gas produced using downward delivery
- bubble gas produced through limewater
36
Percentages of gasses in the air
- nitrogen = 78%
- oxygen = 21%
- carbon dioxide = 0.04%
- argon and other gasses = less than 1%
37
Describe using phosphorus to calculate percentage of oxygen in the air
- phosphorus on evaporating basin on water in bell jar and use hot glass rod to heat it
38
Why must the solution to test for halides be acidified?
prevent the formation of other precipitates
39
Test for chloride ions
- add potassium chloride to a test tube with water and then add a few drops of silver nitrate
- positive result = whiter precipitate forms
40
Test for bromide ions
- to a test tube containing water add potassium bromide and then silver nitrate contact prevent
- positive result = cream coloured precipitate forms
41
Test for iodide ions
- to a test tube containing water add potassium iodide and then add silver nitrate
- positive result = yellow precipitate formed
42
name the four most abundant gases in dry, unpolluted air
- nitrogen = 78%
- oxygen = 21%
- argon = <1%
- CO2 = 0.04%
43
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
44
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%
45
symbol equation of reaction of copper with oxygen
2Cu (s) + O2 (g) => 2CuO (s)
46
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
47
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
48
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
49
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%
50
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)
51
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)
52
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)
53
define thermal decomposition
a reaction where heat causes a compound to break down into its simpler components
54
what do metal carbonates thermally decompose into?
metal oxide and carbon dioxide
55
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)
56
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
57
what type of gas is carbon dioxide?
greenhouse gas
58
what is a greenhouse gas?
a gas in the earth's atmosphere that traps heat, contributing to the greenhouse effect and global warming
59
name one human source of carbon dioxide emissions
thermal decomposition of calcium carbonate in the production of cement produces large volumes of CO2 and contributes to global warming
60
explain the greenhouse effect
- the earth is warmed by light waves from the sun
- the earth produces infrared waves
- some infrared waves escape into outer space
- greenhouse gases in the atmosphere increase
- more radiation is trapped and the temperature rises
- the earth maintains a temperature suited to life
