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CHEMISTRY PRACTICALS > Methods > Flashcards

Methods Flashcards

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1
Q

Calorimetry - 8

A
  • Make up standard solutions of different known concentrations
  • Choose a suitable filter with the complimentary colour
  • Zero colorimeter with water
  • Measure absorbance of standard solutions
  • Plot calibration graph of absorbance vs concentration
  • Measure unknown
  • Read off concentration from calibration curve
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2
Q

Calorimetry: order/rate of reaction

A
  • Use a suitable filter with the complementary colour
  • Zero with water
  • Put a sample of the reaction mixture into the colorimeter
  • Take absorbance readings at set time intervals
  • Convert absorbance readings to concentrations using the calibration curve
  • Plot graph of concentration v time
  • Find half-lives from graph
  • Constant half-life = first order
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3
Q

Carbonates reacting with HCl - 9

A
  • The mass of a weighing bottle containing the carbonate is measured
  • Transfer 50 cm3 of 2 mol HCl [an excess] from a measuring cylinder to a conical flask
  • Add Na2CO3 to acid in flask to saturate acid with CO2
  • So no gas given off when carbonate reacts with acid dissolves in acid
  • Cotton wool plug placed in neck of flask and flask and acid weighed
  • Weighed carbonate is added to acid in flask and cotton wool plug quickly replaced in neck of flask to prevent loss of acid spray
  • Mass of empty weighing bottle is measured
  • Reaction in flask stopped, flask left for 10 minutes to allow CO2 to diffuse from flask
  • Mass of flask and contents after reaction are measured
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4
Q

Recrystillisation - 10

A
  • Heat the impure sample with hot solvent
  • With a minimum amount until solid just dissolves
  • Filter – vaccum filtration used so solution remains hot
  • Leave solution to cool
  • Crystals formed when solution cools
  • Vacuum filter off crystals
  • Wash with cold solvent - minimises further loss of product but ensures any soluble impurities left washed through
  • Air dry/oven in temperature lower than solid melting point
  • First filtration of hot solution removes insoluble impurities
  • After crystallisation soluble impurities stay in solution
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5
Q

Mass spec

A
  • Sample vapourised and ionised
  • Ions are accelerated
  • To the same kinetic energy
  • Move into drift region
  • Heavier ions move across to detector more slowly
  • Different masses take different times to reach detector
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6
Q

Rates of iodine reaction: methods 3

A
  • Concentration of iodine by titration with thiosulfate
  • Colour / absorbance of iodine by colorimetry
  • Acidity – concentration of H+ by pH meter
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7
Q

Potassium manganate titration - 10

A
  • Fill burette with KMnO4 / MnO4– solution
  • Use graduated pipette for sodium ethanedioate
  • Place known amount of solution in flask
  • Add excess sulfuric acid
  • Warm
  • Titrate until pink colour persists
  • Add manganate dropwise near end
  • Repeat for concordance
  • No need for indicator as MnO4 2- is only coloured reagent
  • Colour change takes place during reaction from colourless to pale pink
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8
Q

TLC 11

A
  • Draw pencil-line near bottom of plate
  • Place drops of mixture on the line
  • Place plate in solvent, line above solvent level and add lid
  • Allow solvent to rise through spots
  • When solvent nears top of plate, remove plate
  • Dry plate
  • Transfer to fume cupboard to evaporate solvent
  • Locate spots by adding fluorescent dye then viewing under UV light/iodine gas
  • Circle spots
  • Compare heights/position of spots from mixture with the 3 standard compounds OR calculate Rf values of spots and compare with those of the standards
  • Repeat process after further recrystallisation
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9
Q

Strength of haloalkane C-X bond - 12

A
  • Dissolve haloalkane in ethanol in test tubes
  • Stand in beaker of hot water
  • Add solution of silver nitrate
  • Start timing
  • Ethanol solvent as haloalkanes don’t dissolve in water
  • Hot water needed reaction too slow in cold
  • Equal amounts/volumes of reactant for ‘fair test’
  • precipitate forms/tubes go cloudy
  • Note time on first appearance
  • Precipitates caused by halide ions reacting with silver ions
  • Shorter time means faster rate
  • Rate of hydrolysis in order iodo(fastest), bromo and chloro
  • Bond strengths increase in above order
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10
Q

Thermal stability of carbonates - 11

A
  • Crush lumps of calcium carbonate to a powder using a pestle and mortar
  • Add calcium hydroxide to distilled water and filter
  • Glass test tube/boiling tube to contain the solid fitted with a bung carrying a delivery tube which dips into a solution of calcium hydroxide in a test tube/boiling tube.
  • Tube is heated and is approximately horizontal
  • Gas is passed through limewater
  • Measure time for cloudiness to first appear
  • Measure time taken to obscure a cross on paper
  • Longer time has greater thermal stability
  • Takes longer to go cloudy down the group
  • Equal mass of MgCO3 and CaCO3 and same volume of limewater
  • Same volume and concentration of calcium hydroxide solution
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11
Q

Enthalpy of solution - 3

A
  • Place known volume/mass of water in a polystyrene beaker
  • Weigh out a known mass of the salt and add to water with stirring
  • Measure temperature of water before and after
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12
Q

Group 2 reaction with water - 7

A
  • Measuring vol of hydrogen per unit time
  • Fair testing, same no of moles of metal, same surface area, same temperature
  • Gas bubbles produced
  • Metal decreases in size/disappears
  • Faster rate of reaction for Ba
  • Ca cloudier than Ba
  • Both metals react to produce hydroxides and hydrogen gas
  • Hydroxides more soluble down the group
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13
Q

Flame test - 2

A
  • Nichrome wire dipped in sample and concentrated HCl

- Placed in blue/roaring Bunsen flame

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14
Q

Making a soluble salt with metal/insoluble base - 5

A
  • Add together acid for anion and metal/base for cation until fizzing stops/reaction complete
  • Filter
  • Partially evaporate
  • Fully evaporate to produce crystals
  • Filter and dry
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15
Q

Rate of reaction: titration 3

A
  • Withdraw sample using pipette at given times
  • Run into conical flask
  • Titrate quickly with known concentration of NaOH in burette
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16
Q

Heating to constant mass - 2

A
  • Heat, cool and weigh

- Repeat until mass constant

17
Q

Difference between paper and thin layer chromatography

A

Stationary phase is: silica/alumina in TLC not paper

18
Q

Diluting conc solution to form standard solution

A
  • Vol to use: final conc/initial conc x volume required
  • Transfer vol to use to volumetric flask
  • Use a dropping pipette to fill solution to required volume with distilled water in volumetric flask
19
Q

Standard solution -11

A
  • Calculate mass of solute needed
  • Weigh mass of solute into weighing bottle [zero bottle first]
  • Transfer into beaker, carefully washing out weighing bottle with jet of distilled water and allowing washing to drop into beaker
  • Add a small amount of distilled water and stir with glass stirring rod until all solute has dissolved
  • Transfer solution into 1dm3 volumetric flask containing 500cm3 of distilled water using glass funnel
  • Use distilled water to rinse inside of beaker and glass stirring rod at least twice and pour washings into volumetric flask
  • Shake flask gently
  • Fill up with distilled water until close to actual mark
  • Add more distilled water using a pipette drop by drop after removing funnel and rinsing it properly
  • Until lowest level of meniscus is on mark when at eye level
  • Stopper flask and invert several times
20
Q

How can filters be tested to see which is the appropriate complementary colour? 2

A
  • Try different filters with the solution

- Select filter showing maximum absorption

21
Q

Seperation of substances insoluble in water with impurities that dissolve in water

A
  • Pour mixture into separating funnel
  • Add water
  • Shake funnel
  • Run off bottom aqueous less dense layer
  • Swirl top layer with anhydrous sodium sulfate for 20 mins
  • Filter
22
Q

Filtration - 3

A
  • Pour mixture into Buchner funnel with filter paper at bottom
  • Below funnel have sealed side arm flask attached to a vaccum line
  • Reduced pressure in flask will force liquid through funnel
23
Q

Compare smells of different esters - 8

A
  • Add 1 drop of conc sulfuric acid to each test tube
  • Add 10 drops of RCOOH to sulfuric acid in one test tube
  • Add 10 drops of alcohol to mixture
  • Carefully lower tube into beaker of hot water
  • After 1 minute remove tube
  • When cool, pour mixture into boiling tube half full of sodium carbonate solution
  • Smell product by wafting odour towards nose with hand
  • Repeat with different combinations of COOH and alcohol
24
Q

Reflux - 4

A
  • Boil a liquid in a flask attached to a vertical / upright condenser for a prolonged time
  • Mixture evaporates into vapour
  • Vapour then condensed and returned to mixture as liquid drops back into the flask
  • Allows any substance initially evaporating to be fully oxidised
25
Q

Distillation - 7

A
  • Heat in flask
  • With a still head containing thermometer
  • If it evaporates at room temp then have a cooled collecting vessel
  • The condenser is horizontal and attached at the side
  • Keep condenser cool with running water in a tube at either side to minimise loss of substance through evaporation
  • Mixture are evaporated and condensed and collected in vessel at boiling point
  • Mixture is separated
26
Q

How can Rf values be calculated for amino acids? 4

A
  • Spray ninhydrin solution [developing agent] onto paper to turn spots purple
  • Circle spots with a pencil
  • Measure distance travelled by solvent from baseline to solvent front
  • Measure distance travelled by amino acid by measuring from baseline to spots
  • Calculate Rf: distance travelled by spot/distance travelled by solvent
27
Q

Acid base titration - 9

A
  • Use a graduated pipette to add 25 cm3 of alkali to a clean conical flask
  • Add a few drops of indicator
  • Put the conical flask on a white tile to see colour change more easily
  • Fill the burette with acid and note the starting volume.
  • Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix
  • Stop adding the acid when the end-point is reached
  • Note the final volume reading: this is the rough titre
  • Now do accurate titration: run acid into within 2cm3 of end point, then add the acid dropwise
  • Repeat for 3 concordant titres
28
Q

Making insoluble salts - 4

A
  • Pick 2 solutions with ions needed and mix
  • Salt precipitates out
  • Filter from solution
  • Wash and dry on filter paper
29
Q

Making soluble salts with alkali - 6

A
  • Titrate acid using indicator with alkali [soluble bases] to know amount of alkali needed to neutralise acid
  • Repeat titration to combine these volumes without indicator
  • Filter
  • Partially evaporate
  • Fully evaporate to produce crystals
  • Filter and dry

CHEMISTRY PRACTICALS (2 decks)

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