core practicals Flashcards
draw a diagram to show how the volume of gas can be measured
recall the method for measuring the volume of gas
- ensure acid is in excess so that calcium carbonate is the limiting reagent
- add known mass of CaCO3 to the acid
- measure the volume of CO2 released using measuring cylinder
- repeat + change mass of CaCO3 slightly
what errors could occur when measuring the volume of a gas using the inverted cylinder method
molar vol might be lower than expected- some CO2 may dissolve in the water
recall the method for preparing a standard solution
- weigh mass of solute required and transfer to beaker
- pour distilled water into breaker and ensure all of the solute has dissolved
- transfer solution into volumetric flask and ensure none of it spills
- rinse the beaker to ensure all of the solution is left behind
- fill the flask up to the line with distilled water until the bottom of the meniscus is touching the line, replace the stopper and shake the flask- make sure it doesnt over fill
what error could occur when preparing a standard solution
some solute may not have transferred from the weighing boat
how would you find the concentration of a solution of HCL experimentally
- unknown conc of substance (HCL) titrated against a known conc of a solution
method:
- pipette 25cm3 of HCL into a volumetric flask and make up the rest with distilled water
- pour 25cm3 sample of HCL solution into a conical flask and add a few drops of phenolphthalein
- pour NaOH into a burette and titrate the contents of the flask against NaOH
- record titre
- repeat until you have concordant values
what should you make sure to do when using a titration to find the conc. of HCL to get accurate results
- rinse pipette with HCL before measuring out sample
- calibrate pipette- make sure theres no air bubbles in the tip
- rinse burette with NaOH
recall the method to measure the rate of hydrolysis of haloalkanes
- place equal volumes of silver nitrate into 3 test tubes
- add equal volumes of ethanol into 3 different test tubes
- add 3 drops of haloalkane to their respective labelled test tubes
- add the silver nitrate to the test tubes containing haloalkanes at the same time and start the stop clock
- place the test tubes with haloalkane and silver nitrate into a hot water bath at the same time
- record the time taken for a precipitate to form in each of the test tubes
recall the process for the oxidation of ethanol/primary alcohol
- flask contains alcohol and dichromate
- heat flask with contents
- hold the bunsen burner to have more control over the heat so that the mixture doesnt bubble too much
- colour change from orange to green (alcohol oxidised to aldehyde)
- condenser in horizontal position so that aldehyde vapour can travel down the condenser and collect in the second flask -> distillation
- colour change from orange to green when ethanol oxidised to aldehyde because Cr ion reduced to Cr3+ which is green
why does refluxing of aldehydes occur in the vertical position
- vertical position so that aldehyde can condense and fall back into flask after evaporating so that the second oxidation can take place
- aldehyde to carboxylic acid
what is refluxing
- continuous evaporation and condensation without the loss of product
- exothermic
how would you oxidise secondary alcohols
only use reflux as only one oxidation takes place
what should you make sure to do when oxidisng alcohols
- dont seal apparatus- risk of pressure build up + explosion
- distillation- thermometer bulb is next to arm of condenser
- distillation- oxidised once, second flask should only contain aldehyde
recall the process of chlorination of 2-methylpropan-2-ol using conc. HCL
- measure out 2-methyl-propan-2-ol into a measuring cylinder and keep in warm water
- pour the alcohol into the separating funnel and replace the stopper
- measure out conc HCL into another measuring cylinder in a fume hood
- slowly pour the conc HCL into the separating funnel with the alcohol
- stopper the funnel and invert it gently for 20 mins
- set up distillation apparatus
- discard the aq (bottom) layer in the separating funnel to a beaker
- add sodium hydrogen carbonate solution to the funnel to neutralise excess acid, shake the funnel and run off the aq layer
- run the organic layer (which is left in the funnel) into a conical flask containing anhydrous sodium sulphate and swirl the flask
- pour the organic liquid into a pear shaped flask for distillation and add anti-bumping granules
- distill collect the liquid
how would you test the product of the chlorination of 2-methylpropan-2-ol using conc. hcl
- add ethanol to a test tube
- add a few drops of the product into that test tube containing ethanol and place in a 50 C water bath
- add silver nitrate to the test tube
- white precipitate should form
