Chemistry (Solutions and Gases) Flashcards
(46 cards)
Precipitation Reaction
(Definition)
When two solutions of soluble substances are mixed together and react to form an INSOLUBLE substance which will not dissolve and so a PRECIPITATE forms
Precipitate
(Definition)
An insoluble solid that forms when two solutions are mixed and a chemical reaction occurs, resulting in a compound that is not soluble in the solvent
Solubility Rules for Salts
Soluble in Water:
All potassium, sodium, ammonium salts.
All nitrates.
All common halides (e.g. chlorides) except silver halides and lead halides.
All common sulphates except lead (II) and calcium sulphate, barium sulphate.
Insoluble in Water:
All common carbonates EXCEPT sodium, potassium and ammonium carbonates.
All common hydroxides EXCEPT sodium, potassium and ammonium carbonates
What happens when an ionic compound dissolves in water?
The ions separate and become spread out among the water molecules. The ions no longer have anything to do with each other.
What happens when some salts are insoluble in water?
If solutions containing those ions are mixed, the insoluble salt forms as a solid as the solutions are mixed. This solid is known as a precipitate and the reaction as precipitation.
What happens when salts are soluble in water?
Often when solutions of two salts are mixed, no such precipitation reaction will take place and the ions will remain dissolved in water.
How to make an insoluble salt
1) Mix together solutions of two soluble salts that provide the ions you need
for +ve ions, use a nitrate salt solution (as all nitrates are soluble)
for -ve ions, use a sodium/potassium solution (as all sodium/potassium salts are
soluble)
2) Filter off the precipitate, wash and dry
The History of the Atmosphere
1) Volcanoes - released water vapour (H2O), carbon dioxide (CO2), nitrogen (N2), methane (CH4), ammonium (NH3), etc. which formed the atmosphere
2) Earth’s temperature falls to 100°C. Water vapour condenses. The first rain falls and oceans form. [Mainly CO2 and N2 at this point]
3) The first plants evolve - photosynthesis introduces O2, a new element and removes a lot of CO2, killing some bacteria and making some evolve to become ALGAE.
4) The first animals evolve - e.g. the comb jellyfish. Fish = O2<CO2
5) Animals die and get sunk to the bottom of the sea and get covered in sediment.
6) Fossil Fuels formed as plants and animals die. If dead organic matter gets buried quickly and is heated with lots of pressure and after time passes, fossil fuels will form.
7) About 400 million years ago, the atmosphere is very much like todays - E.g. Nitrogen = 78% Oxygen = 21%
8) Present day - Carbon Dioxide level now at 0.04%
How are Sedimentary Carbonate Rocks formed?
Carbon dioxide in atmosphere => plants during photosynthesis => animal tissues when plants = eaten => dead bodies in oceans => sedimentary carbonate rocks formed
How are Calcium Carbonate Rocks formed?
Carbon dioxide in atmosphere => dissolved in oceans => reacted to form insoluble carbonate compounds => fell into sea bed => calcium carbonate rocks formed
What happened to the Atmosphere?
CO2 is taken up by plants and turned into new plant material called carbon sinks/stores/locks during photosynthesis. Then animals eat the plant and the C is transferred to the animal tissues, including bones, teeth and cells. Over millions of years ago, the dead bodies of huge numbers of these living organisms accumulated at the bottom of vast oceans where they formed calcium carbonate rocks like limestone. Some were crushed by movements of the Earth and heated within the crust and formed fossil fuels. in this way much of the CO2 from the ancient atmosphere became locked up within the Earth’s crust.
CO2 also dissolved in the oceans, forming insoluble carbonate compounds which fell to the bottom and helped form carbonate rocks.
At the same time, small amount of NH3 and CH4 remaining in the atmosphere reacted with the oxygen formed by the plants. The O2 removed these toxic gases and the levels of N2 and CO2 increased.
The Atmosphere today.
N2 = Nitrogen = 78%
O2 = Oxygen = 21%
Ar = Argon = <1%
CO2 = Carbon Dioxide = 0.04%
Explain why the volume of air decreases during the reaction between oxygen and heated copper.
The Oxygen reacts with the copper, therefore removing it from the air.
How to find the % of O2 in the air
React the oxygen with heated copper.
Air is going to be passed over some copper turning that are being heated strongly in this experiment. As air passes over the copper, the oxygen in the air will react with the copper. By seeing what volume of air remains after the reaction, we can work to the % of oxygen in the air. The air will be passed over the hot copper several times to give all the oxygen chance to react.
% O2 in Air Experiment
Equipment
- 100cm3 gas syringe x2
- Copper turnings
- Bunsen Burner
Catalytic Decomposition
(Definition)
A chemical reaction where a single compound breaks down into two or more simpler compounds or elements in the presence of a catalyst. The catalyst speeds up the decomposition process without being consumed or changed itself.
Hydrogen Peroxide (+manganese oxide) => oxygen + water
H20(aq) (+MnO2) => O2(g) + 2H2O(l)
Hydrogen Peroxide (+manganese oxide) => oxygen + water Experiment
Equipment
- Conical Flask
- Bung
- Thistle Funnel
- Delivery Tube
- Boiling Tube
- Ice Cream Tub
- Water
Name the following properties of Oxygen:
1) Colour
2) Odour
3) Density (compared to air)
4) Solubility in water
5) Effect of glowing splint
6) Effect of Universal Indicator
1) Colourless
2) Odourless
3) Very similar to air - as air is full of oxygen
4) Soluble in water - for example fish need to breathe in water
5) Relights splint
6) Stays green: neutral: 7-ish pH
The Chemical Test for Oxygen (O2)
Relights a glowing splint
What are Hydrocarbons?
Most fuels used today are hydrocarbons - compounds that contain hydrogen and carbon only. When a hydrogen is burned in a plentiful supply of oxygen, it produces two main products - water and carbon dioxide.
The 2 tests for Water
1) Anhydrous copper sulphate, which turns white powder to blue when in contact with water
2) Cobalt chloride (paper), which starts as a baby blue, then turns pink
The 1 test for Carbon Dioxide
Limewater turning milky/cloudy from clear
The 1 test for Hydrogen
When a lit splint is introduced into a test tube containing hydrogen, the hydrogen rapidly burns, creating a characteristic squeaky or popping sound as it reacts with oxygen in the air
