Core practicals Flashcards
(13 cards)
how do you calculate percentage uncertainty
uncertainty / measure amount x 100
during a titration, why
core practical 1: describe how to measure the molar volume of a gas
when given ethanoic acid and calcium carbonate
-measure 30cm3 of ethanoic acid using a 50cm3 measuring cylinder and place into a boiling tube
-set up a delivery tube and bung onto the boiling tube. fill a trough with water and place a 100cm3 measuring cylinder filled with water upside down into the trough. make sure the delivery tube goes into the measuring cylinder
-measure 0.5g of calcium carbonate using a mass balance and place in the boiling tube
-quickly replace the bung with the delivery tube
-set a timer for 10 minutes
-measure the volume of gas produced in the measuring cylinder
core practical 2: describe how to conduct a titration to find the concentration of sodium hydroxide
when given solid sulfamic acid, sodium hydroxide and methyl orange
-make a standardised solution of aqueous sulfamic acid
-weigh an empty test tube. add 2g of sulfamic acid to the test tube. reweigh the test tube
-add distilled water and mix with a stirring rod
-pour into a 250cm3 volumetric flask along with the washings and fill the rest with water
-set up apparatus for titration. the burette contains the acid and the conical flask has the sodium hydroxide
-pour a 25cm3 aliquot of NaOH and a few drops of methyl blue to the conical flask
-conduct a rough titration, then conduct more titrations till you get concordant results
-the colour change is yellow to orange
core practical 3: describe how to conduct a titration to find the concentration of a solution of hydrochloric acid
when given HCl, NaOH, phenolphthalein
-make a standardised solution of HCl
-use a glass pipette to measure 25cm3 of HCl and transfer to a 250cm3 volumetric flask. fill the flask with distilled water
-set up the apparatus for a titration. HCl will be in the conical flask and NaOH in the burette
-pour a 25cm3 aliquot of HCl solution and a few drops of phenolphthalein into the conical flask
-conduct a rough titration. repeat the titration till you get concordant results
-the colour change will be from colourless to a pale pink
core practical 4: describe the method to investigate the rate of hydrolysis of chloro, bromo and iodo halogenoalkanes
when given ethanol, silver nitrate and the halogenoalkanes
-fill 3 test tubes with 5cm3 of ethanol and 5cm3 of silver nitrate
-place one in a water bath with boiling water for 5 minutes
-place 4 drops of 1-chlorobutane into the test tube, start a stop watch
-when a white precipitate forms stop the timer
-repeat for 1-bromobutane which has a cream precipitate and 1-iodobutane which has a yellow precipitate
core practical 4: describe the method to investigate the rate of hydrolysis of primary, secondary, tertiary halogenoalkanes
when given ethanol, silver nitrate and the halogenoalkanes
-fill 3 test tubes with 5cm3 of ethanol and 5cm3 of silver nitrate
-place one in a water bath with boiling water for 5 minutes
-place 4 drops of 1-bromobutane into the test tube, start a stop watch
-when a cream precipitate forms stop the timer
-repeat for 2-bromobutane and 2-methyl-2-bromobutane which has a yellow precipitate
core practical 5: describe how to conduct and oxidation of ethanol
when given ethanol, acidified potassium dichromate(vi),
-add 10cm3 of acidified potassium dichromate(vi) and anti-bumping granules to a pear shaped flask
-set up the apparatus for heating under reflux
-mix 2cm3 with 5cm3 of water
-place the pear shaped flask in a beaker of iced water and add the ethanol down the side of the condenser into the flask slowly
-attach the apparatus
-heat the flask so that the solution boils for 10 minutes
-set up the apparatus for distillation
-heat the flask but don’t let it boil
-distilled ethanol will come out of the condenser into a beaker
core practical 6:
when given 2-methylpropan-2-ol, sodium hydrogencarbonate solution, powdered anhydrous calcium chloride, anhydrous sodium sulfate, silver nitrate, sodium hydroxide and nitric acid
-pour 20cm3 of 2-methylpropan-2-ol and 70cm3 of HCl into a large conical flask, place a bung, swirl, remove the bung to release the gas, repeat for 20 minutes
-2 layers will form, the top is the crude product
-add 5g of powdered anhydrous calcium chloride to the flask and swirl till it has dissolved. this reacts with any unreacted alcohol to make sure it is in the lower aqueous layer
-transfer the mixture into a separating funnel, allow it to settle, run off and discard the lower layer
-add 20cm3 of sodium hydrogencarbonate solution to the separating funnel. add a bung, swirl, remove the bung to release the gas, repeat a few times. CO2 gas will be produced.
-run off and discard the lower aqueous layer
-repeat this washing with sodium hydrogencarbonate for 10 minutes
-run off the organic layer into a small conical flask. add a spatula of anhydrous sodium sulfate, place a bung and swirl. let it settle until it looks colourless, and swirl again a few times
-decant the organic liquid into a pear shaped flask
-set up the apparatus for distillation
-2-chloro-2-methylpropane has a boiling point between 50℃ - 52℃
core practical 6: why is powdered anhydrous calcium chloride added to the crude product
Anhydrous calcium chloride is added to the crude product because it is a drying agent, so it absorbs the water made during the reaction between 2-methylpropan-2-ol
It also causes the crude product to separate into 2 layers
core practical 6: why is aqueous sodium hydrogencarbonate added
to remove any unreacted hydrochloric acid
produces sodium chloride, water and carbon dioxide
the bung needs to be removed to release the carbon dioxide, and the lower layer needs to be discarded to remove the water
core practical 6: why is anhydrous sodium sulphate added to the organic layer
it is a drying agent
so it will remove any water left in the solution by forming sodium sulfate hydrate, which is a solid
so when the organic solution is decanted the solid sodium sulfate hydrate will be removed
when conducting a titration explain what actions may be carried out just before the end-point to ensure the volume of acid added at the end-point is accurate
-swirl the conical flask so that all acid and alkali has reacted and the indicator is homogenous in the solution
-add the acid drop by drop so you don’t overshoot the end-point
-compare the colour of the solution at the end-point to that of a previous titration to ensure consistency of end-point colour
-place the conical flask on a white tile to clearly see the colour change
