Chemistry Required Practicals Flashcards
(18 cards)
Preparation of a pure dry salt
Heat acid, add copper oxide until no more reacts.
Filter to remove excess solid.
Evaporate gently, then leave to crystallise.
Dry crystals with filter paper.
Safety precautions for preparation of a pure dry salt
Wear safety goggles as sulphuric acid is corrosive.
Make sure hair is tied back.
When the Bunsen burner is not in use, turn it off or leave it on the orange safety flame.
Neutralisation/Titration
Use a pipette to add 25 cm³ sodium hydroxide to a conical flask.
Add phenolphthalein indicator (pink in alkali).
Fill a burette with sulfuric acid and record the initial reading.
Add acid slowly while swirling until the solution turns colourless.
Record final reading and calculate titre (acid volume used).
Repeat to get concordant results, then calculate mean titre.
Use balanced equation and C = mol / vol to find concentration.
Safety precautions of a titration
Wear safety goggles when working with acids.
Tie hair back.
Report any broken glassware immediately.
Electrolysis of copper chloride
Add 50 cm³ copper chloride to a beaker.
Insert electrodes into the lid (not touching).
Connect to DC power supply using crocodile leads.
Set to 4 V and switch on.
Use litmus paper near positive electrode (tests for chlorine).
After a few mins, switch off and observe electrodes.
Record observations (e.g. copper at cathode, bubbles at anode).
Safety precautions for electrolysis (copper chloride)
Safety goggles must be worn.
Room should be well ventilated because large quantities of chlorine gas is toxic.
Temperature changes
Add 25 cm³ HCl to a polystyrene cup in a beaker.
Measure and record the starting temperature.
Add 5 cm³ NaOH, stir with thermometer, and record maximum temp.
Repeat by adding more 5 cm³ portions (up to 40 cm³ total).
Repeat experiment and calculate mean max temps.
Safety precautions for temperature changes practical
Wear safety goggles.
Rate of reaction using volume of gas produced method
Add 50 cm³ HCl (1.0 M) to a conical flask.
Add 3 cm magnesium strip, quickly bung the flask and start timer.
Record volume of gas every 10 seconds until reaction stops.
Repeat with 1.5 M HCl.
Plot a graph: volume of gas vs time, one curve for each concentration.
Rate of reaction using colour change or turbidity method
Add 10 cm³ sodium thiosulfate + 40 cm³ water to flask (8 g/dm³).
Place flask on a black cross.
Add 10 cm³ HCl, swirl, and start timer.
Stop timer when cross disappears.
Repeat with different thiosulfate : water volumes to change concentration.
Repeat experiment and calculate mean times.
Safety precautions for measuring the rate of reaction
Wear safety glasses.
Take care when using glassware.
Chromatography
Draw a pencil line 1 cm from bottom of chromatography paper.
Add small spots of inks A–D + unknown (U) along the line.
Place paper in a beaker with solvent, keeping line above solvent.
Let solvent run up paper, then remove before it reaches the top.
Allow paper to dry, then measure spot + solvent distances.
Calculate Rf value for each spot:
Rf = distance moved by spot ÷ distance moved by solvent
Safety precautions for chromatography
Don’t put food colouring in eyes - may cause irritation
Flame test for metal ions
Pour 1 cm³ of each chloride solution into 5 test tubes.
Clean nichrome wire in dilute HCl.
Dip wire in solution, then hold in blue Bunsen flame.
Record flame colour.
Repeat for other solutions, clean wire after each test.
Add 1 cm³ unknown chloride to test tube.
Dip wire in solution, hold in flame.
Compare flame colour to known chloride results
Carbonate Ion (CO₃²⁻) Test
Place 2 cm³ limewater in a clean test tube.
Add dilute HCl to the unknown solution.
If bubbles form, use delivery tube to transfer gas to limewater.
Repeat for known sodium carbonate solutions to confirm carbonate ions.
Sulphate Ion (SO₄²⁻) Test
Add 10 drops of dilute HCl to unknown solution.
Add 2 cm³ barium chloride solution.
Pour 1 cm³ of known sodium solutions into separate test tubes.
Add 5 drops of dilute HCl, then 2 cm³ barium chloride.
Halide ion (Cl⁻, Br⁻, I⁻) test
Add 10 drops of dilute nitric acid to the unknown solution.
Add 1 cm³ silver nitrate solution.
Pour 1 cm³ of known sodium solutions into separate test tubes.
Repeat steps 1 and 2 for the known solutions.
Record colour of the precipitate in each test tube.
