required practicals

• Practical - Separation: Paper Chromatography

  separates substances in a mixture, dyes in ink -

  
  

  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

  10. end result is pattern of spots - chromatogram
• Practical - Separation: Filtration

  separates insoluble solids from liquids -

  
  

  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

  2. can be used in purification as well, solid impurities in reaction mixture can be separated using filtration
• Practical - Separation: 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

  
  

  quick, but only use if soluble salt doesn't decompose when heated
• Practical - Separation: Crystallisation


  separates soluble solids in solutions, even if solid decomposes when heated -

  
  

  1. pour solution into evaporating dish, gently heat. some solvent evaporates and solution gets concentrated

  2. once some solvent evaporates or when crystals start forming (point of crystallisation), remove dish from heat and allow to cool

  3. salt forms crystals as it's insoluble in cold, highly concentrated solution

  4. filter crystals from solution, leave in warm place to pat dry. or use drying oven/desiccator
• Practical - Separation: 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
• Practical - Separation: 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

  
• Practical - Titration


  found out quantity of acid/alkali needed to neutralise exactly. can work out concentration of acid/alkali -

  
  

  1. for alkali, use pipette + filler to add set volume of alkali to conical flask, two or three drops of phenolphthalein (colourless in acid, pink alkali)

  2. use funnel to fill burette with acid of known concentration at eye level (safety goggles), record initial volume of acid in burette

  3. use burette tap dripping open and swirl to distribute alkali, slow near end-point

  4. indicator changes colour (colourless in acid), white tile shows clear change, when neutralised

  5. record final volume of acid in burette, take difference from initial reading and use to calculate vol. of acid to neutralise alkali

  
  

  increase accuracy by taking rough first go for approximate end-point and repeat until concurrent

  (3 within 0.10cm3), calculate mean and ignore anomalies
• Practical - Energy Transferred in Reaction

  1. measuring energy released by chemical reaction in solution by taking reagent temp. mix in polystyrene cup and measure temperature at end 2. energy is lost to surroundings, affecting readings so reduce with polystyrene cup in beaker of cotton wool for more insulation, lid for less evaporation energy loss

  3. works for neutralisation, or reactions between metals and acids/carbonates

  4. can investigate different variables on energy transferred like mass and concentration of reactants used
• Practical - Temperature Change Factors

  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
• Practical - Chromatogram


  result of chromatography analysis -

  Rf value is ratio between distance travelled by dissolved substance and distance travelled by solvent.

  Rf = distance travelled by substance / distance travelled by solvent.

  Rf is on scale of 0 - 1.0.

  run pure sample and mixture in chromatography and check Rf value of a spot to see if they match up and check pure substance is in the mixture.

  Rf value depends on solvent, test mixture against reference Rf of pure substance and if a spot matches all solvent Rf's then it's in the mixture, if not, it's not in the mixture.
• Practical - calculating rate of reaction


  rate of reaction = amount of reactant used or product formed / time e.g. in g/s.

  how quickly reactants are used up, or products are formed, over time.
• Practical - RofR precipitation and 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.
• Practical - RofR Change in Mass (gas given off)

  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.
• Practical - RofR volume of gas given 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.
• Practical - Concentration of acid with magnesium

  1. add set vol. of dilute HCl to conical flask, carefully place on mass balance.

  2. add magnesium ribbon to acid, quickly plug flask with cotton wool.

  3. start stopwatch, record mass on balance at regular time intervals.

  4. plot results in table and work out mass lost for each reading, plot graph of time(x) and mass lost(y).

  5. repeat with more concentrated acid solutions. same amount of magnesium and same vol. of acid to make fair test (only conc. changes)

  6. three graphs show higher concentration increases RofR
• Practical - 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.

  6. results show effect of increasing HCl concentration on RofR added to sodium thiosulfate excess.

  7. higher conc. means quicker RofR, less time for cross to disappear.

  8. this doesn't produce graphs, just readings.
• Practical - 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.

  4. retest distilled solution for sodium chloride to check it's all gone. retest pH to make sure it's neutral.
• Anion tests


  Dilute acids and limewater for carbonates, let carbonates and dilute acids react and connect through an air tube to limewater. Carbonate will form CO2 and make limewater cloudy. Sulfates with Barium chloride and HCl, add couple of drops of dilute HCl and dilute Barium Chloride to sulfate and there will be white precipitate. Nitric acid and silver nitrate for halides, add drops of dilute nitric acid and silver nitrate solution and iodide gives yellow precipitate, bromide cream and chloride white
• Metal flame tests


  Lithium-crimson

  Sodium-yellow

  Potassium-lilac

  Calcium-orange/red

  Copper-green
• Metal NaOH precipitate


  Calcium-white

  Copper-blue

  Iron 2+-green

  Iron 3+-brown

  Aluminium-white at first then colourless in excess NaOH

  Magnesium-white