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Flashcards in Methods Deck (29):

Calorimetry - 8

- 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


Calorimetry: order/rate of reaction

- 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


Carbonates reacting with HCl - 9

- 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


Recrystillisation - 10

- 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


Mass spec

- 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


Rates of iodine reaction: methods 3

- Concentration of iodine by titration with thiosulfate
- Colour / absorbance of iodine by colorimetry
- Acidity – concentration of H+ by pH meter


Potassium manganate titration - 10

- 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


TLC 11

- 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


Strength of haloalkane C-X bond - 12

- 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


Thermal stability of carbonates - 11

- 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


Enthalpy of solution - 3

- 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


Group 2 reaction with water - 7

- 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


Flame test - 2

- Nichrome wire dipped in sample and concentrated HCl
- Placed in blue/roaring Bunsen flame


Making a soluble salt with metal/insoluble base - 5

- 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


Rate of reaction: titration 3

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


Heating to constant mass - 2

- Heat, cool and weigh
- Repeat until mass constant


Difference between paper and thin layer chromatography

Stationary phase is: silica/alumina in TLC not paper


Diluting conc solution to form standard solution

- 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


Standard solution -11

- 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


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

- Try different filters with the solution
- Select filter showing maximum absorption


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

- 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


Filtration - 3

- 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


Compare smells of different esters - 8

- 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


Reflux - 4

- 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


Distillation - 7

- 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


How can Rf values be calculated for amino acids? 4

- 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


Acid base titration - 9

- 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


Making insoluble salts - 4

- Pick 2 solutions with ions needed and mix
- Salt precipitates out
- Filter from solution
- Wash and dry on filter paper


Making soluble salts with alkali - 6

- 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