Practicals Flashcards
How do you set up an electrolysis cell?
1) You need a container for the solution (the electrolyte), and two electrodes connected to a battery or power pack.
2) You can hook a graphite electrode to the end of the beaker.
3) The electrode connected to the negative terminal of the battery becomes the cathode, and the electrode connected to the positive terminal becomes the anode.
4) You can collect products in the gas state in small test tubes so that you can identify them later.
5) Remember that electrolytes and their products may be harmful, so wears eye protection.
Common mistakes that lead to inefficient electrolysis cells and how to improve.
- make sure that the end of each electrode is under the surface of the electrolyte
- make sure that the electrical connections are made securely; try cleaning the crocodile clips, for example
How to produce hydrated copper(II) sulfate crystals.
- Half fill the 250cm3 beaker with boiling water from a kettle.
- Add 15 cm3 of sulfuric acid to a boiling tube and place in the beaker of hot water.
- Weigh out 2.00 g of copper(II) oxide onto a weighing boat.
- Add a quarter of the copper oxide to the boiling tube with sulfuric acid. Lift the tube and
agitate the mixture before returning it to the water. - Add the remaining copper(II) oxide to the boiling tube in three equal amounts, agitating the
mixture between each addition. - Leave the boiling tube for 5 minutes, agitating the mixture every minute.
Purification of copper(II) Sulfate solution
- Place the filter paper in the funnel and place the funnel over the conical flask.
- Pour the mixture from the boiling tube through the funnel, into the conical flask.
Production of hydrated copper(II) sulfate crystals
- Record the mass of the crystallising dish.
- Boil the solution in the conical flask for 3 minutes using the bunsen burner and tripod. 11. Using tongs pour the solution from the conical flask into the crystallising dish.
- Allow the solution to cool for 5 minutes
Possible errors when crystallising
- The solution may not have been fully transferred to the crystallising dish so some copper sulfate may be lost. To improve this, deionised water should be used to rinse the conical flask. Add washings to the solution in the crystallising dish.
- Some anhydrous copper sulfate may be produced during evaporation of the solvent, this can be improved by reducing the time that the bunsen burner heats the solution for.
Safety precautions when crystallising
● Sulfuric acid is an irritant so wear safety glasses and wash your hands after using it.
● Copper(II) oxide is harmful if ingested so wash hands after use and use in a well ventilated
lab.
● Copper(II) sulfate crystals cause skin and eye irritation. Avoid touching and wash hands
immediately if there is any contact with skin.
● Clear up any chemical spillages or broken glassware immediately.
● Take care when using the Bunsen burner. Tie hair back. Leave on the orange safety flame
or turn gas off when not in use.
● The conical flask will be hot after heating so only touch it with the tongs. If the flask is
touched, hold the burn under cold running water for up to 10 minutes, depending on the severity.
How do you carry out evaporation?
Place the solution in an evaporating basin. Gently heat the solution with a Bunsen Burner.
How do you separate an insoluble solid from a liquid?
Filtration- Place the filter paper into a funnel. Place the funnel in a beaker. Pour the solution into a funnel. Solid remains in the filter paper.
How would you separate coloured soluble substances?
Paper chromatography: Place a spot of the sample on a pencil line which is 2cm from the bottom of a piece of chromatography paper. Place paper in a beaker of solvent (solvent level must be below pencil line).
Why are ink spots placed above the level of the solvent in the beaker?
The ink would dissolve in the solvent rather than moving up the chromatography paper.
What affects the Rf value?
The solvent and the stationary phase
Purpose of simple and fractional distillation
Simple- separate one liquid from a solution
Fractional- separates several different liquids
