PAPER 1 req practicals

Question 1

Prepare 250cm3 standard solution containing accurately weighed mass

Answer 1

Accurately weigh out dry sample of acid using 2dp balance
Transfer to beaker and reweigh weighing boat to determine mass transferred
Diissolve acid in small volume of distilled water
Stir with glass rod
Transfer to volumetric flask and rinse equipment
Add washings
Make up to 250cm3
Shake and invert

Question 2

Determine the conc of unknown solution of HCl using 0.1moldm3 solution of NaOH

Answer 2

Rinse burette with NaOH to remove contamination
Use a volumetric pipette to transfer 25cm of HCl to conical flask
Add 2 drops of phenolphthalein
Slowly add NaOH and continuously swirl
Rinse burette and sides of conical flask
Stop at first permanent colour change and record volume of NaOH added
Repeat until concordant data achieved
Use concordant data to calculate mean titre
n = cxv = moles NaOH
[NaOH] an [HCl]1:1 ratio
[HCl] = n/0.025

Question 3

Measure enthalpy change when copper sulfate dissolves in water and how to calculate deltaH

Answer 3

Measure 50cm3 of water using burette
Transfer to polystyrene cup with lid
Measure 4g of CuSO4 using accurate 2dp balance
Use thermometer to take temp of water for 4 mins to establish inital temp
Pour copper sulfate into water at min 5
Reweigh weighing boat to estalish mass transferred
Replace lid and stir
Continue recording temp and minute intervals up to 15 minutes
Plot temp against time
Extrapolate back to point of addition and determine deltaT
q=mcat
deltaH = q/n
mol = mass/mr

Question 4

How to use pH probe to produce a calibration curve

Answer 4

pH probe may give inaccurate readings
Take 3 buffer solution with known accurate pHs
Use pH probe to measure pH of first solution and record
Rinse pH probe with distilled water
Repeat for other 2 buffer solutions
Plot a graph of pH probe readings against pH value
Draw line of best fit
For each reading in titration refer to line of best fit and adjust reading accordingly