Practical Skills Flashcards
(12 cards)
5 marks
Using a 2 d.p. balance, record the mass of an empty crucible.
› Add a small amount of hydrated magnesium sulfate to the crucible, re-weigh and record the mass.
• Gently heat the crucible for 2 minutes, allow to cool and re-weigh.
• Continue heating and re-weighing to constant mass to ensure that all water of crystallisation has been removed.
Use the mass of the crucible and hydrated salt and mass of the empty crucible to calculate the mass of the hydrated magnesium sulfate used in the experiment.
• Use the mass of the crucible and anhydrous salt and mass of the empty crucible to calculate the final mass of anhydrous magnesium sulfate.
• Calculate the mass of water removed by calculating the difference in mass between the mass of the hydrated and anhydrous salts
• Work of the moles of anhydrous salt by dividing the mass of anhydrous salt by the molar mass of MgSO4 (120.4)
• Work of the moles of water by dividing the mass of water removed by the molar mass of H2O (18)
• Calculate the mole ratio between anhydrous salt to water by dividing the moles of water by the moles of anhydrous salt.
Using a 2 d.p. balance, record the mass of a strip of magnesium ribbon.
• Place the magnesium ribbon in a conical flask.
• Using a measuring cylinder, measure out an excess amount of dilute hydrochloric acid.
, Carefully add the acid to the flask and quickly fit a bung connected to a gas syringe to record the mass of gas produced.
• When the syringe has stopped moving record the final volume of gas produced.
Plot graphs (on same axes) of volume of H2(g) against time.
• Calculate initial rate of reaction for each concentration of HClaq) by drawing tangents to curves at to.
• Compare the gradients of the 3 tangents.
• If reaction is first order with respect to HC|(aq) the results should show that when the concentration of the HClaq) is halved, the rate approximately halves.
Express the initial rate for each experiment using 1/time
• Plot a graph of initial rate (y-axis) against [l’(aq)] (x-axis)
• Straight line graph through the origin = first order with respect to [l’(aq)]
Add a small amount of dilute nitric acid to a test-tube containing a small quantity of each solution. The one which bubbles contains the carbonate ion and is therefore potassium carbonate.
• To a small amount of the four remaining solutions, add a small quantity of barium chloride solution. The two which give white precipitates contain the sulfate ion.
• To a small amount of the two solutions which gave the white precipitate with Ba (aq) add a small quantity of sodium hydroxide solution and warm gently. Test any gas produced with damp red litmus paper. The one which turns the damp litmus paper blue contains ammonium ions and is therefore ammonium sulfate. The one which does not is sodium sulfate.
• To small amounts of the two remaining solutions add a small quantity of silver nitrate solution.
The expected result would be a white precipitate and a cream precipitate. To these add a small quantity of dilute aqueous ammonia solution. The white precipitate should dissolve confirming the presence of chloride ions. This is therefore sodium chloride. The cream precipitate should not dissolve confining the presence of bromide ions. This is potassium bromide.
In what order should you carry out the carbonate, sulfate and halide ions test and why?
CaSH- carbonate-> sulfate ->halide
Neither sulfate or halide ions produce gas with dilute acid so the carbonate test is carried out first.
• Carbonate ions also react with barium ions to give a white precipitate (BaCO3 is insoluble) so the sulfate test is carried out after the carbonate has been identified and eliminated.
• Both carbonate ions and sulfate ions react with aqueous silver ions to give precipitates (Ag2SO4 is insoluble )so the halide test needs to be carried out once the carbonate ions and sulfate ions have been identified and eliminated.
REFLUX
Carefully add 10cm3 of cyclopentanol to a pear-shaped flask.
• Slowly add 4cm3 of concentrated phosphoric acid to the flask.
• Fit a Leibig condenser to the flask for reflux.
Connect the lower rubber tube to the cold water tap and turn on the water.
• Heat the mixture at around 90°C using a water-bath/ electric heating mantle for around 10 minutes
DISTILLATION
Set up the condenser for distillation.
• Heat the mixture using a water-bath/electric heating mantle at 50°C (boiling point of cyclopentene 44°C) until a small quantity of product has been collected.
PURIFICATION USING A SEPARATING FUNNEL
Pour the distillate into a separating funnel
• Add a small quantity of distilled water and allow layers to separate (cyclopentene will be in upper layer)
• Run out the aqueous layer and discard
• Collect the organic layer in a small conical flask
• Add a small quantity of anhydrous CaCl2 (drying agent) to the flask and swirl
• Filter the mixture into a small container
Draw a diagram to show the set up for purification using a separating funnel;
Mr aspirin = 180
• mol aspirin required = 8.4/180 = 0.0467
• mol 2-hydroxybenzoic acid required = (0.0467/85.5)x100
= 0.0546
• mass 2-hydroxybenzoic acid required = 0.0546x138 =
7.53g
