Core practical 2 & 3 - Titrations and preparations of solution

Question 1

How do you prepare a solution with a known concentration ?

Answer 1

1. Measure out the known mass of a substance and dissolve it with distilled water in a beaker
2. Pour this solution into a volumetric flask (250cm^3)
3. Rinse the beaker by adding washings to collect any liquid or undissolved substance
4. Transfer the washings into the volumetric flask and fill up to the line
5. The bottom of the meniscus should be on the marked line
6. Shake the volumetric flask gently to allow for uniform concentration

Question 2

How to do titrations (steps)

Answer 2

• rinse equipment (burette with acid, pipette with alkali, conical flask with distilled water) •pipette 25 cm3 of alkali into a conical flask
• touch the surface of alkali with a pipette ( to ensure the correct amount is added) •adds acid solution from the burette
• make sure the jet space in the burette is filled with acid
• add a few drops of indicator and refer to a colour change at endpoint •phenolphthalein [pink (alkali) to colourless (acid): endpoint pink colour just disappears] [use if NaOH is used] •methyl orange [yellow (alkali) to red (acid): endpoint orange] [use if HCl is used] •use a white tile underneath the flask to help observe the colour change
• add acid to alkali whilst swirling the mixture and add acid drop-wise at endpoint •note burette reading before and after addition of acid
• repeats titration until at least 2 concordant results are obtained- two readings within 0.1 of each other

Question 3

Burette accuracies

Answer 3

• Rinse burette with the solution that will be placed in it
• Make sure the JET SPACE is filled with the solution
• Read from the bottom of the meniscus
• Near the end point add drop by drop while swirling

Question 4

Experimental notes : accuracy and etc

Answer 4

• Use a pipette for accuracy when measuring samples of acid