Elements of Life: Titrations

Question 1

Describe techniques and procedures used to prepare a standard solution of a specific concentration from a solid ( 6 marker ) ( 8 steps )

Answer 1

1. Weigh solute = mass of solute is the difference between the
   mass of the weighing bottle and solute and the
   weighing bottle once emptied
2. dissolve solute in distilled water in a beaker and stir the mixture with glass rod
3. use a filter funnel to transfer solution to a clean rinsed volumetric flask
4. Rinse the beaker and stirring rod well with
   distilled water, making sure that all the washings go into the volumetric flask.
5. Add distilled water to the solution in flask swirling at intervals to mix the contents
6. use a dropping pipette to further add distilled water until bottom of the meniscus is level with the mark on the neck of the flask
7. Insert the stopper in the flask and invert it several times to ensure complete mixing

Question 2

2 specific pieces of equipment used in a titration

Answer 2

Pipette ( 25cm^3 )

Burette ( tap= accuracy )

Question 3

Concordant results

Answer 3

Are within I’m 0.1 of each other

Question 4

Method of titration

Answer 4

1. Use pipette to transfer 25cm3 alkali to conical flask + add methyl orange indicator
   
   • b4 rinse with distilled water + alkali
   • draw up with pipette filler
2. Place acid in burette + fill to 0 line
   
   • make sure no air bubbles
   • b4 rinse with distilled water + acid
3. Carry out rough titration to get an idea of end point
   
   • take initial reading from burette ( to 0.05 )
   • add acid to alkali whilst swirling
   • stop when indicator show permanent colour change (yellow —> straw colour ( pink if over end point )
   • record final reading from burette
4. accurate titration
   
   • add acid within 2cm3 of endpoint
   • then add dropwise
   • until colour change (yellow —> straw (pink if over) )
5. Work out acid used to neutralise alkali
   
   • titre = final reading - initial reading
6. Repeat titration
   
   • until 2 concordant results ( within 0.1cm3)
   • take average of concordant results only

Question 5

What is the purpose of a trial titration

Answer 5

Allows you to find an approx value for the volume of acid needed to react with alkali / base

Question 6

Definition of tire

Answer 6

Difference between final burette reading and initial burette reading