Practicals paper 1/3 Flashcards
(25 cards)
Practical 1 (Paper 1+3)- Topic AoS
How to make up a standard (volumetric) solution ?
Stage 1: transfers known mass of solid
a) Weigh the sample bottle containing the solid on a (2 dp) balance
b) Transfer to beaker* and reweigh sample bottle
c) Record the difference in mass
Stage 2: Dissolves in water
a) Add distilled / deionised water
b) Stir (with a glass rod) or swirl
c) Until all solid has dissolved
Stage 3: Transfer, washing and agitation
a) Transfer to volumetric / graduated flask using a funnel
b) With washings
c) Make up to 250cm3 / mark with water
d) Shakes/inverts/mixes
Practical 1 (Paper 1+3)- Topic AoS
How to reduce percentage error ?
To reduce the Percentage Error(PE) in a titration you could use a larger titre volume.
Eg if the burette volume used was originally 25cm3 then suggest to use a larger volume(i.e. 45cm3)
Why is it important to remove any air bubbles from the burette tap?
The volume of the air bubble would be counted in the burette reading
If the bubble was not removed from the burette tap, how would this affect the titre?
Increase it
Why is it important to remove the funnel used to fill up the burette before starting a titration?
Solution drops could fall from the funnel into the burette and affect the burette reading
Why is it good practice to swirl the conical flask and rinse the walls of the conical flask with distilled water during a titration?
Ensures all reactants mix and no reagent is left unreacted on sides of flask
Why does adding water to the conical flask not affect the titre?
It doesn’t change the number of moles in the conical flask
Why is a conical flask is preferred to a beaker for a titration?
There is less chance of splashing liquid while swirling
What should the burette be washed with before a titration?
Whatever solution it is going to be filled with
Why is it bad practice to wash the burette with water before a titration?
Water would decrease the concentration of the solution in the burette, which would increase the titre
What should the pipette used to fill up the conical flask be washed with?
Whatever solution is going to be put in the conical flask
Why is it bad practice to wash the pipette with water before using it to fill up the conical flask?
Water would take up space in pipette and decrease the number of moles transferred to the conical flask, which would reduce the volume needed from the burette (titre) for complete reaction
Practical 2 (Paper 1, 2 + 3) Topic Energetics
Measurement of an Enthalpy Change
Describe how you would carry out an experiment to determine the enthalpy of solution of anhydrous magnesium chloride.
Stage 1 Method
(1a) Measures water with named appropriate apparatus
(1b) Suitable volume/mass / volume/mass in range 10 – 200 cm3/g
(1c) Into insulated container / polystyrene cup (NOT just ‘lid’)
(1d) Add known mass of MgCl2(s)
(1e) Use of ‘before and after’ weighing method. NOT ‘added with washings’
Stage 2 Measurements (could mark from diagram)
(2a) Record initial temperature (min 2 measurements)
(2b) Record T at regular timed intervals for 5+ mins / until trend seen
(2c) Plot T vs time
Stage 3 Use of Results (3a and 3b could come from diagram)
(3a) Extrapolate lines to when solid added (to find initial and final T)
(3b) Tfinal – Tinitial = ΔT / idea of finding ΔT from graph at point of addition
(3c) q = mcΔT
(3d) amount = mass/Mr (0.80/95.3 = 8.39 × 10−3 mol)
(3e) ΔHsoln = –q/8.39 × 10−3 or in words
what can you do to improve burning a fuel ?
Reduce the distance between the flame and the beaker
Put a sleeve around the flame to protect it from drafts.
what can you do to improve adding a solid to a solution or adding 2 solutions together to reduce heat loss ?
Add a lid/Insulate the beaker
Practical 4 (Paper 1 +3) Topic Group 2+7
Inorganic Test Tube reactions
what is the eqn for Ba2+ (aq) and SO42- (aq) ?
Ba2+(aq) + SO42−(aq) → BaSO4(s)
what is the eqn for Mg2+ (aq) and OH- (aq)
Mg2+(aq) + 2OH−(aq) → Mg(OH)2(s)
Write all the eqns for AgNO3 and all the halide ions
Ag+(aq) + Cl−(aq) → AgCl(s)
Ag+(aq) + Br−(aq) → AgBr(s)
Ag+(aq) + I−(aq) → AgI(s)
AgCl and dilute NH3 eqn
AgCl(s) + 2NH3(aq) → [Ag(NH3)2]+(aq) + Cl−(aq)
AgBr and Conc NH3 eqn
AgBr(s) + 2NH3(aq) → [Ag(NH3)2]+(aq) + Br−(aq)
ionic eqn between ammonium and NaOH
NH4+ + OH- → NH3 + H2O
ionic eqn between carbonate ions and acid
Acid + Carbonate Base → Salt + Water + CO2
2H+ + CO32- à CO2 + H2O
Practical 8 (Paper 1 +3) Measuring the EMF of an electrochemical cell
It is difficult to ensure consistency with the setup of a standard hydrogen electrode. A Cu2+(aq) / Cu(s) electrode (Eo = +0.34 V) can be used as a secondary standard.
A student does an experiment to measure the standard electrode potential for the TiO2+(aq) / Ti(s) electrode using the Cu2+(aq) / Cu(s) electrode as a secondary standard.
A suitable solution containing the acidified TiO2+(aq) ion is formed when titanium(IV) oxysulfate (TiOSO4) is dissolved in 0.50 mol dm−3 sulfuric acid to make 50 cm3 of solution.
(b) Describe an experiment the student does to show that the standard electrode potential for the TiO2+(aq) / Ti(s) electrode is −0.88 V
The student is provided with:
- the Cu2+(aq) / Cu(s) electrode set up ready to use
- solid titanium(IV) oxysulfate (Mr = 159.9)
- 0.50 mol dm−3 sulfuric acid
- a strip of titanium
- laboratory apparatus and chemicals.
Your answer should include details of:
- how to prepare the solution of acidified TiO2+(aq)
- how to connect the electrodes
- measurements taken
- how the measurements should be used to calculate the standard electrode potential for the TiO2+(aq) / Ti(s) electrode.
Stage 1: Preparing solution
(1a) Weigh 7.995 / 8.00 g TiOSO4
(1b) Dissolve in / add (allow react with) (0.50 mol dm-3) sulfuric acid
(1c) transfer to volumetric flask and make up to the mark
Stage 2: Set up cell
Content can be shown in a labelled diagram
(2a) piece of Ti immersed in (1 mol dm−3 acidified) TiO2+(aq) / the solution
(2b) (connect solutions with) salt bridge or description
(2c) (connect metals through high R) voltmeter
Stage 3: Measurements and calculation
(3a) record voltage/potential difference/emf of the cell
(3b) Ecell = ERHS – ELHS
Ecell = Ecopper – Etitanium
(3c) ELHS = ERHS – Ecell OR Ecell should be +1.22 V if Cu on RHS (or −1.22 if Cu electrode on LHS)
Practical 9 – (Paper 1 +3) Investigate how pH changes when a weak acid reacts with a strong base and when a strong acid reacts with a weak base
“A student has an unknown weak acid of unknown concentration and a
bottle of 0.5 mol dm-3 NaOH.
Explain, using brief practical details, how you would determine the Ka of the weak acid. [6]”
1a Measure 25 cm3 of acid into a beaker/conical flask using volumetric pipette.
1b Use a pH probe to measure the initial pH
1c Add 1cm3 of a 0.1 mol dm-3 NaOH from a burette swirl and record the pH
1d Repeat until the NaOH is in excess (around 40 cm3 added)
2a Plot a graph of pH against vol NaOH added in cm3
2b Use the vertical section to find the volume of NaOH needed for neutralisation
2c The half neutralisation point is half the volume of neutralisation.
3a Read off the pH at the half neutralisation point.
3b At half neutralisation ka = [H+]/pKa=pH
3c Ka = 10-pH
