Chemistry Experiments Flashcards
Investigate how to determine the formula of a metal oxide by combustion
1) weigh a crucible with a lid
2) Place a piece of magnesium ribbon about 10cm long in the crucible and weigh the crucible and contents
3) Set up the apparatus : Crucible containing magnesium ribbon with lid on top, on a tripod with pipe clay triangle, on a Bunsen burner
4) Heat the crucible strongly (a roaring flame)
5) lift the lid every few seconds
6) when the reaction is finished, allow the crucible and contents to cool
7) weight crucible and contents
8) when magnesium burns it does so with a bright white flame. Magnesium oxide, a white powder, is produced in the reaction
9) a lid is on the crucible to prevent white powder escaping but the list must be lifted every few seconds to allow oxygen into crucible to react with magnesium
10) we can work out magnesium mass by subtracting mass of crucible from mass of crucible + magnesium.
Investigate how to find the value of “x” in a hydrated salt formula (water of crystallisation)
1) usually when you heat a salt that contains water of crystallisation, water is driven off, leaving the anhydrous salt behind.
2) hydrated barium chloride is a commonly used example because the barium chloride itself doesn’t decompose even on quite strong heating.
3) To find x, you need to find the ratio of the number of moles of Barium Chloride to the number of moles of water.
Describe test for hydrogen gas
A lit splint is held to the mouth of the tube.
The hydrogen explodes with a squeaky pop.
The hydrogen combines explosively with oxygen in the air to make water.
Test for oxygen gas
A glowing splint is put into the tube containing the gas. Oxygen relights a glowing splint.
Test for carbon dioxide gas
The CO2 is bubbled through limewater. CO2 turns limewater milky/chalky/cloudy white
Limewater is calcium hydroxide solution. CO2 reacts with it to form a white precipitate of calcium carbonate.
Test for chlorine gas
A piece of damp litmus paper is put into the test tube or held over its mouth.
Chlorine is a green gas that bleaches the damp litmus paper
If blue litmus paper is used for this test, it will go red first (chlorine dissolved in water to form an acidic solution) and then white.
Test for ammonia gas
Hold a piece of damp red litmus paper at the mouth of the test tube.
Ammonia turns the litmus paper blue.
Investigate the electrolysis of molten lead (II) bromide
1) add lead (II) bromide into a crucible and heat so it will turn molten, allowing ions to be free to move and conduct an electric charge.
2) Add two graphite rods as the electrodes.
3) Negative bromide ions move to the anode and lose two electrons to form bromine molecules.
4) there is bubbling at the anode as brown bromine gas is given off.
5) Positive lead ions move to the cathode and gain electrons to form grey lead metal which deposits on the bottom of the electrode.
Describe how to carry out an acid-alkali titration
Describe a chemical test for water
- Add anhydrous, white copper sulfate
- Which turns from white to blue
Describe a physical test for water
- Boil the liquid
- Measure the boiling point which should be 100 degrees celcius
Détermine the percentage of oxygen in air
- measure the volume between the final mark on the scale and the tap (stopcock)
- Fill the burette with water up to lowest mark, 50.0 mL, and then let it drain into a small measuring cylinder
- Measure the volume of water
- Add a little water to moisten the inside of the burette
- Make sure the tap is closed and sprinkle some iron filings or push a piece of iron wool into the bottom of the burette
- Invert the burette into a trough of water and clamp the burette Vertically
- Note and record the position of the water level
- After 3-4 days note the new position of the water level
Investigate metals reacting with acids
- Wear some safety glasses before handling Acids
- Using a small measuring cylinder, add 5 cm3 of dilute hydrochloric acid to each of three test tubes
- Add about 1 cm length of magnesium ribbon to the first tube, observe and note down what you see
- Use a lighted splint to test for any gases given off
- To the second test tube add a few pieces of iron filings and to the third some zinc turnings
- Observe what happens, test for any gases and note down your observations
- Repeat the experiment with dilute sulfuric acid
A polystyrene cup can act as a calorimeter to find enthalpy changes in a chemical reaction
- A fixed volume of one reagent is added to the calorimeter and the initial temperature taken with a thermometer
- An excess amount of the second reagent is added and the solution is stirred continuously
- The maximum temperature is recorded and the temperature rise calculated
Enthalpy of combustion experiments
- A fixed volume of water is measured and transferred to the copper can
- The spirit burner containing, for example, an alcohol, is weighed on a 2 d.p. balance
- The initial temperature of the water is measured and recorded
- The alcohol is ignited and the water is stirred continuously
- When the temperature has risen by about 20 degrees the flame is extinguished and the spirit burner is re-weighed
- The final temperature of the water is recorded
