Unit 3 - Lesson 12: Tests for Water and Gas Flashcards
(51 cards)
What do humans need to survive?
H2O (water), O2 (oxygen), CO2 (carbon dioxide), and N (nitrogen)
What do plants produce for us?
O2 (oxygen)
How can we test a sample of ice to see if it has water?
Add anhydrous copper (II) sulfate to a sample of the ice. If it has water, it will turn blue. If it stays white, it doesn’t have water.
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What is an endothermic reaction?
An endothermic reaction is one which takes in energy from the surroundings, usually in the form of heat and usually shown by a fall in temperature of the surroundings.
What is an exothermic reaction?
An exothermic reaction is one which gives out energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature of the surroundings.
What is the meaning of anhydrous?
A substance is anhydrous if it contains no water.
What kind of reaction is adding water?
An exothermic reaction. It releases heat energy.
What kind of reaction is removing water?
An endothermic reaction because to take away the water, you need to heat it.
What substance can we use to test an atmosphere for CO2?
Limewater. If it turns cloudy, CO2 is present.
How can we test for oxygen?
How can we test for hydrogen?
Oxygen, in a test tube, will relight a glowing splint.
Hydrogen, in a test tube, will make a lit splint go pop!
State the names and proportions of gases we’d need on Mars to be just like Earth.
Nitrogen - 78%
Oxygen - 21%
Argon - 0.9%
Carbon Dioxide - 0.04%
Describe 2 practicals that could be used to investigate the proportion of oxygen in the atmosphere.
Practical 1 → Finding the proportion of oxygen in an air sample using the metal ‘Iron’ (Fe).
Firstly, soak iron wool in acetic acid.
Secondly, push the wool into a measuring cylinder.
Thirdly, invert this into a beaker of water.
Fourthly, record the starting position of the water.
Fifthly, the water in the measuring cylinder will rise as oxygen enters to react with the Fe (iron).
Sixthly, leave for one week or until it stops rising; this is the final volume of air.
Practical 2 → Finding the proportion of oxygen in an air sample using the non-metal ‘Phosphorus’ (P).
Firstly, place phosphorus in a tube and attach a glass syringe at either end.
Secondly, make sure one of the syringes is filled with air and the other empty.
Thirdly, heat the phosphorus and use the syringes to pass air over it.
Fourthly, the air will decrease as oxygen is used up. Measure starting and final volumes using the scales on the syringes.
State the formula used to calculate the percentage of oxygen in a sample.
Percentage of oxygen = Start volume - Final volume/Start volume x 100
(% of Oxygen = Start volume (subtract) Final volume (divided by) Start volume (multiplied by) 100)
Mars already has an atmosphere rich in CO2. State an experiment you could do to make CO2 in a planet with no CO2.
- What apparatus is needed?
- What is the chemical equation?
- What is the method?
You could use thermal decomposition to make CO2. For example:
Copper (II) carbonate →(heat) metal oxide + carbon dioxide
The apparatus needed: clamp stand, delivery tube, clamp, test tubes, metal carbonate, Bunsen burner, and limewater.
Firstly, heat copper (II) carbonate. It’s a green powder.
Secondly, copper (II) oxide will be made, which is black.
Thirdly, the CO2 will turn the limewater cloudy.
What could happen to the temperature of Mars if there was too much CO2?
The temperature would increase.
A scientist finds water trapped in a large salt plains on a new planet. State the name of a salt with water molecules incorporated into its lattice. Choose one option from a - d.
a) Anhydrous
b) Hydrated
c) Crucible
d) Oxidised
b) Hydrated
(Relating to Q16) State the name of the water trapped in the salt. Choose one option from a - d.
a) Water of crystallisation
b) Anhydrous water
c) Water vapour
d) Evaporated residue
a) Water of crystallisation
How many moles of water are there in these salts?
a) CuSO4.4H2O
b) MgSO4.5H2O
a) 4
b) 5
Find the X in BaCl2.XH2O using the results table below.
Mass of crucible | 30g
Mass of crucible + BaCl2.XH2O | 32.44g
Mass of crucible + BaCl2 | 32.08g
BaCl2.2H2O.
Explanation:
Step 1: Mass of hydrated salt + anhydrous salt
32.44 - 30 = 2.44
32.08 - 30 = 2.08
2.44 + 2.08 = 4.52
Step 2: Number of moles of water lost = mass / Mr
32.44 - 32.08 / (1x2) + 16
= 0.36 / 18
= 0.02 mol
Step 3: Number of moles of anhydrous salt made = mass / Mr
32.08 - 30 / 137 + (35.5 x 2)
= 2.08 / 208
= 0.01 mol
Step 4: Work out the ratio of moles of anhydrous salt to moles of water
Anhydrous salt : water
0.01 : 0.02
1 : 2
Therefore, BaCl2.2H2O
You take a sample of air after 30 years terraforming on Mars. You take it back to your on-site lab for testing.
a) Describe a test for CO2.
b) Describe a test for ammonia.
c) Describe a test for hydrogen gas.
a) Pass a sample of air through limewater. If it turns cloudy, CO2 is present.
b) The simplest test is the presence of a bad smell. However, because ammonia is a danger to your eyes, nose, throat & respiratory system, it’s safer to check for the gas with damp red litmus paper. If it turns blue, ammonium (NH^4+) is present.
c) Place a burning splint near the gas and it’ll make a pop sound.
You want to test the ice caps of Mars for water. Describe the test to use.
Add anhydrous copper (II) sulfate (CuSO4) to a sample of the melted ice. If the CuSO4 turns blue, water is present.
State the boiling point of pure water.
100 degrees Celsius
State the freezing point of pure water.
0 degrees Celsius
What change of state is occurring at the boiling point of pure water?
Liquid to gas
