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Aim
Aim
To determine Ka for a weak acid
To determine Ka for a weak acid
These videos & activities will support your laboratory work and help you with the analysis of your results
These videos & activities will support your laboratory work and help you with the analysis of your results
Equipment
Equipment
100 cm3 of 0.1 mol dm−3 ethanoic acid solution ● 100 cm3 of 0.1 mol dm−3 sodium hydroxide solution ● datalogger and pH probe or pH meter ● stand, clamp and boss for pH probe ● 50 cm3 burette ● burette stand ● 250 cm3 conical flask ● 25 cm3 pipette and filler ● phenolphthalein indicator
Procedure
Procedure
Set up the datalogger to read the pH, or calibrate the pH meter.
2. Pipette 25.0 cm3 of 0.1 mol dm−3 ethanoic acid solution into a 250 cm3 conical flask.
3. Fill a burette with sodium hydroxide solution.
4. Add two or three drops of phenolphthalein to the conical flask.
5. Titrate the ethanoic acid with sodium hydroxide solution until the mixture just turns pink.
6. Pipette a further 25.0 cm3 of 0.1 mol dm−3 ethanoic acid solution into the 250 cm3 conical flask.
7. Record the pH of this solution
Things to consider CPAC 2b
Things to consider CPAC 2b
CPAC 2b - Carries out techniques or procedures methodically, in sequence and in combination, identifying practical issues and making adjustments when necessary.
· Prepare apparatus for titration:
1. Wash out burette with alkali
2. Add alkali to burette using a funnel at eye level with glasses on
3. Remove air bubbles from tap
4. Record initial burette level
5. Pipet 25cm3 acid to a conical flask using a bulb pipette and safety filler
6. Use pH metre to accurately measure pH
7. Any practical issues are identified and adjustments made as necessary
· Carry out titrations:
1. Titrate swirling the flask and with good control over the tap
2. Achieve drop wise addition near the end point
3. Read titre to nearest 0.05cm3
· Accurate use of pipette to measure 25.0cm3 portions
Things to consider CPAC 4a
Things to consider CPAC 4a
CPAC 4a – Makes accurate observations relevant to the experimental or investigative procedure.
· Obtain 2-3 concordant results
· Read scales correctly on all pieces of apparatus (teacher to check one)
· Read from bottom of meniscus when using burette (teacher to check one)
· Use pipet so that bottom of meniscus is on line
Read the Hazcards COSHH information for the chemicals used in the practical so that you are aware of how to keep yourself and others safe 38A,91A, 32
Read the Hazcards COSHH information for the chemicals used in the practical so that you are aware of how to keep yourself and others safe 38A,91A, 32
Wear a lab coat and use eye protection.
Tie long hair back.
Sodium hydroxide solution is an irritant.
Required Resources
Required Resources
Core Practical 9 - Student sheet.docxConsult CLEAPSS Hazcards®38A,91A, 32. Perform a risk assessment using up-to-date information before this practical is carried out
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