required practicals

• paper chromatography

  1. draw insoluble pencil line at bottom of filter paper sheet

  2. add spot of ink to line and place in solvent water

  3. solvent depends on mixture, some compounds dissolve well in water, others need ethanol

  4. make sure ink isn't touching solvent (so not dissolved)

  5. lid on container to stop solvent evaporating

  6. solvent seeps up paper, carrying ink

  7. each different dye moves at different rates so dyes separate. each dye forms a single spot

  8. any insoluble, in solvent, dyes stay at baseline

  9. when solvent has nearly topped out, take paper out beaker and dry
• filtration

  1.filter paper folded in cone in funnel, solid left in filter paper, liquid in beaker. use with insoluble solid to be separated from liquid reaction mixture
• evaporation

  separates soluble solids in solutions -

  1. pour solution into evaporating dish

  2. slowly heat solution, solvent evaporates and solution becomes more concentrated. crystals start to form

  3. keep heating evaporating dish until only dry crystals are left
• separating rock salt

  rock salt: mixture of salt and sand. both compounds, salt dissolves in water and sand doesn't, difference in physical properties allows separation -

  1. grind mixture to make small, dissolvable salt crystals

  2. stir mixture into water, only the salt dissolves

  3. filter mixture, grains of sand left in filter paper, too big, salt passes through in solution

  4. evaporate water from salt to form dry crystals
• simple distillation

  separates liquid from solution -

  1. heat solution . lowest boiling point evaporates first

  2. vapour cools and condenses and is collected

  3. rest of solution stays in flask

  4. separates pure water from seawater, water evaporates, condenses and is collected as salt is left in flask

  5. only separates substances with very different boiling points, temperature above highest point mixes solutions again - use fractional distillation
• temperature change

  effect of acid concentration on energy released in neutralisation of HCl and NaOH -

  1. 25cm^3 of 0.25mol/dm^3 of HCl and NaOH in separate beakers

  2. place beakers in water bath at 25C until both same temperature

  3. add HCl then NaOH to polystyrene cup with lid

  4. take temperature every 30 seconds and record highest

  5. repeat using 0.5 mol/dm^3 and 1 mol/dm^3 of HCl to see how concentration affects temperature change/energy transferred
• rate of reaction (colour change)

  1. record visual change in reaction if initial solution is transparent, product is precipitates which changes turbidity (cloudiness) of solution.

  2. observe mark through solution and measure how long to disappear.

  3. if reactants are coloured and products colourless, time how long for solution to lose/gain colour.

  4. results are subjective, different people might not agree over when mark disappears. you can't plot a graph of this.
• rate of reaction (change in mass)

  1. measure speed of gas producing reaction with a balance.

  2. as gas' released, disappearing mass is measured on balance.

  3. quicker reading drops, faster reaction.

  4. take measurements at regular intervals, plot rate of reaction graph, find rate more easily.

  5. most accurate method for RofR, mass balance is accurate. but gas is released straight into room.
• rate of reaction (volume of gas give off)

  1. use gas syringe to measure volume of gas

  2. more gas given off in time interval means faster reaction.

  3. gas syringes give volume to nearest cm^3, quite accurate. take measurements at regular intervals, plot Rofr graph, be careful of vigorous reaction as plunger end could fly off.
• concentration of acid with sodium thiosulfate

  1. both chemicals are clear solutions, form yellow sulfur precipitate.

  2. add set vol. of dilute sodium thiosulfate to conical flask.

  3. place flask on piece of paper with cross drawn on. add dilute HCl.

  4.watch black cross disappear through cloudy sulfur, time how long to go.

  5. repeat reaction with different concentration of one of either reactants at a time(not both), and keep vol of liquid the same each time..
• testing and distilling water

  1. test pH with meter, if too high/low, must be neutralised. use titration to neutralise but use pH meter not an indicator that would contaminate.

  2. test for presence of sodium chloride (sea salt), flame test sample for sodium ions (yellow). test for chloride with drops of silver nitrate (white precipitate).

  3. to distil, pour salty water into distillation apparatus, heat flask from below, water boils to steam and leaves dissolved salts in flask. steam condenses as liquid water collected from condenser.