chem practical skills

• making a standard solution

  1. weigh out a precise amount of the solid
  2. add to a small volume of water and dissolve the solid
  3. transfer to a volumetric flask using a funnel
  4. rinse beaker with distilled water and add rinsings to flask
  5. make up to "250cm3" with more water, bung and invert to mix contents
• recrystallisation

  • add very hot solvent to the impure solid just until it dissolves - dont add too much as you want to form a saturated solution
  • filter hot solution through heated funnel to remove soluble impurities
  • leave soln to cool down slowly. crystals will form as product cools
  • remove liquid containing solid impurities from crystals by filtering the mixture using buchner funnel
  • was crystals with ice cold solvent to remove any soluble impurities. leave crystals to dry
• melting and boiling points to test for purity

  Melting point apparatus to determine melting point of organic solid

  • pack small sample of solid into glass capillary tube and place inside heating element
  • increase temp until sample turns from solid to liquid
  • measure a melting range - when it begins to when it stops melting
  • compare value to data book
  • impurities will lower melting point and broaden the range
• describe a method for determining the conc of an unknown solution of (hydrochloric acid), using a 0.1moldm-3 solution of (sodium hydroxide) by acid-base titration

  • rinse burette with base to remove contamination
  • use volumetric pipette to transfer 25cm3 hcl to conical flask
  • add 2 drops of suitable indicator
  • add base to acid and swirl
  • stop at first colour change and record volume of base added
  • repeat until concordant results and calculate mean titre
  • use n=cv to find moles of base added then find conc of acid
• describe how to measure the enthalpy change when (copper sulfate) dissolves in water.

  • measure 50cm3 using a burette/pipette and transfer to polystyrene cup
  • measure 4g of copper sulfate
  • use thermometer to take temp of water each min for 4 mins
  • add copper sulfate at min 5 (do not record temp)
  • reweigh weighing boat
  • replace lid and stir
  • record temp at min intervals for 15 mins
  • plot graph with temp against time
• describe a method to investigate the impact of temp on initial rate of reaction and explanation of how you would handle data recorded

  • use water baths to heat samples of (sodium thiosulfate) to 25, 35, 45 and 55
  • draw x on piece of paper
  • add first sample of (HCl) to first sample of sodium thiosulfate and start timer
  • record time taken for cross to disappear
  • repeat with other temps keeping volumes and concs the same
  • calculate 1/t and plot graph of t against 1/t
• distillation

  • add whatever to round bottom flask with side arm with antibumping granules
  • clamp round bottom flask over electric heater
  • add bung with integrated thermometer which sits at height with side arm. ensure bung is fully sealed
  • attach condenser to side
  • apply heat using electric heater
  • collect distillate when thermometer shows boiling point of whatever
• iodine clock reaction h2o2 + 2I- + 2H+ ---> 2h2o + I2

  • add small amount of (sodium thiosulfate) and starch to beaker
  • add iodine solution
  • record time for blue/black colour to appear
  • dilute the iodine solution so concentration is half the original
  • repeat experiment and record time taken
  • calculate 1/t
  • work out the orders
• continuous monitoring of rate of reactions- gas syringe

  • use burette to measure 50cm3 of (hydrogen peroxide) into conical flask
  • use balance to measure 1g of (manganese dioxide)
  • add catalyst to flask, add bung with delivery tube and start stopwatch
  • record volume of gas released every 10 seconds until syringe is full
  • calculate conc of sodium peroxide remaining for each time point
  • plot conc of h2o2 against time
• producing a calibration curve

  • pH probe may take inaccurate reading so take 3 buffer solutions of known pH and use probe to measure
  • rinse pH with distilled water and repeat with other buffer solns
  • plot a graph of pH probe reading against real pH value
  • draw line of best fit
  • for each reading in titration refer to line of best fit
• method for purifying aspirin (purification of organic solid compound)

  • (filter/decant to remove from reaction mixture)
  • dissolve the crude aspirin in a minimum volume of hot solvent
  • filter through fluted filter paper to remove traces of insoluble impurities
  • slowly cool until aspirin recrystalises (transfer vessel to ice bath)
  • filter using buchner funnel (filtration by reduced pressure)
  • wash with cold solvent
  • dry
• TLC

  • wear gloves to prevent contamination of plate
  • draw pencil line, use capillary tube to add small spot of amino acid mixture to line
  • allow plate to dry, add developing solvent to beaker and place tlc in
  • add lid to beaker to prevent evaporating
  • remove plate when solvent is 1cm from top and mark with pencil line
  • dry plate in fume cupboard
  • visualise plate under UV and mark spot
  • calculate rf value