...Experiments And Processes Flashcards
Describe an experiment that shows how gases travel at different speeds..
1) on one end of a glass tube, insert cotton wool soaked in ammonia solution and in the other insert cotton wool soaked in hydrochloric acid
2) put stopper either end to trap the gases
3) a ring of ammonium chloride forms after a while, closer to the end with hydrochloric acid because ammonia particles are lighter so their velocity is relatively greater
This shows that light particles are faster than heavier ones.
Describe the potassium permanganate experiment to demonstrate diffusion..
1) fill 6 beakers with water
2) out some potassium permanganate in the 1st and mix
3) take 40 mL of the mixture out of the 1st mixture and put in the 2nd
4) repeat with all 6 beakers
With each stage, the amount of potassium permanganate decreases so the colour decreases.
With each dilution there are less potassium permanganate particles in the water.
This shows how a solid (ground potassium permanganate) ca become small enough to become part of a liquid.
Describe a crude demonstration of how diffusion in liquids can be very slow if they are still…
Fill a large beaker up with water and put a small cup in the bottom with some potassium manganate solution inside.
It can take days for the liquids to fully diffuse.
How would you remove ink from water using distillation?
Connect a distillation flask with a thermometer attached to a condenser leading to another flask. Around the condenser there should be a tube with cold water running through it to cool the collected gases down.
1) in the distillation flask, pour the ink / water mixture
2) heat the mixture up to he boiling point of water
3) the water evaporates up the tube and into the condenser
4 the cold water running around the condenser cools the gas which is turned back into water and trickles into the other flask
4) in the original flask you now have pure ink
Note: any liquid put through this process is called a distillate
How do you separate crude oil using fractional distillation?
When crude oils comes out of the ground, it is made up of many different lengths of hydrocarbon chains, and these need to be separated.
- crude oil is fed in at the bottom of a large tower and heated up to about 350 deg C
- any of the shorter chain molecules will boil at this point and turn into vapour, flowing up to the next compartment
- if the compartment is the right temperature it will liquefy, if not it goes up until it finds the right temperature for the relative chain molecules
Describe how you would carry out chromatography..
1) get a strip of chromatography paper
2) draw a line across the paper and on the line put a spot of the sample to analyse
3) put the paper in a solvent, keeping the spot ABOVE the solvent surface
4) as the solvent rises it carries the sample and separates the chemicals at different dissolving points
The solvent travels up the paper in tiny tubes through a process called CAPILLARY ACTION.
The point at which the solvent stops is the SOLVENT FONT.
What was the “gold foil” experiment?
In the gold foil experiment (AKA the Geiger-Marsden experiment) of 1909, Ernest Rutherford aimed alpha particles at gold foil.
Most particles passed through, but a few were deflected and some even bounced back.
Rutherford concluded that:
- most of the atom is empty space
- the atom must also have a dense, positively charged core (this explained why some alpha particles were being diverted)
Describe an experiment to measure oxygen in the air..
Oxygen in the air can be measured by passing a known volume of air over hot copper and measuring the decrease in volume as the oxygen reacts with it.
Copper + oxygen -> copper oxide
2Cu + O2 -> 2CuO
Gas syringes containing air are attached to a tube with some copper turnings, suspended above a lit Bunsen burner.
To make analysis easy, the starting volume of air is often 100 cm 3.
If this case the final calculations should be..
Volume at start: 100 cm 3
Volume at end: 79 cm 3
Volume of oxygen: 100-79 = 21 cm 3
% of oxygen in the air = 21 x 100 / 100 = 21%
NOTE:
There is some air in the tube with the copper turnings which will also react with the hot copper, causing a small error in the final volume recorded
You must let the apparatus cool down at the end of the experiment or the final reading will be too high
How would you create pure oxygen in a lab?
1) some manganese dioxide (MnO2) and water (H2O) are taken in a conical flask with a thistle funnel running into it, and a delivery tube running out of it
2) hydrogen peroxide (H2O2) is added drop by drop down the thistle funnel
3) the oxygen gas escapes via the delivery tube, which leads into a trough of water with a beehive shelf and gas jar attached to it
4) the oxygen gas is collected in the gas jar with the downward displacement of water
2H2O2 -> 2H2O + O2
Hydrogen peroxide -> water + oxygen
NOTE: the MnO2 is used as a catalyst as it speeds up the reaction without actually being used in the reaction
How would you produce carbon dioxide in a lab by use of calcium carbonate (CaCO3)?
CaCO3 + HCl -> CaCl2 + H2O +CO2
1) some pieces of calcium carbonate are out in a round bottom flask which is fixed to a clamp with a thistle funnel running into it and a delivery tube running out of it into a gas jar
2) hydrochloric acid is added to it until the carbon dioxide evolves
3) the CO2 travels up and along the delivery tube and is collected in the gas jar by the upward displacement of air
How would we produce carbon dioxide by use of copper II carbonate (or any metal carbonate)?
1) put some copper II carbonate in a round bottom flask with a delivery tube attached to it, leading to a gas jar
2) heat the flask up with a Bunsen burner
3) the CO2 travels up and along the delivery tube and is collected in the gas jar by the upward displacement of air
Describe the Haber Process..
- an industrial manufacturing process to produce ammonia
- the raw materials for this process are hydrogen and nitrogen
- hydrogen is obtained by reacting methane with steam, or by the cracking of oil
- nitrogen is obtained by burning hydrogen in air; air is 80% nitrogen so when hydrogen is burned in air the oxygen combines with the hydrogen, leaving the nitrogen behind
Nitrogen and hydrogen will react together under the following conditions:
- a high temperature (about 450 deg C)
- a high pressure (about 200 atmospheres; 200 x normal pressure)
- an iron catalyst is present
The reaction is reversible
Nitrogen + hydrogen (»<>«) 2NH3(g)
How do you test for hydrogen in a gas?
A lighted wooden splint goes pop if it is put into a test tube that contains hydrogen. This is because the flame ignites the hydrogen which burns explosively to make a loud sound.
The equilibrium between nitrogen dioxide and dinitrogen tetroxide
http://www.nuffieldfoundation.org/practical-chemistry/le-chatelier’s-principle-equilibrium-between-nitrogen-dioxide-and-dinitrogen-tet
Describe filtration..
Used to separate a powdered solid from a liquid.
This does not work if the solid is dissolved in the liquid.
The liquid (usually water) is passed through filter paper and the solid gathers on the paper.
A liquid passed through this process is called a filtrate.
