4.2 acid-base titrations

Question 1

what is a standard solution

Answer 1

is a solution of known concentration

Question 2

what do we use to make a standard solution accurately

Answer 2

a volumetric flask (either 250cm3 or 100cm3)

Question 3

how do you prepare a standard solution

Answer 3

1.the solid is weighed accurately
2.the solid is dissolved in a a beaker with less dissolved water than necessary to fill the volumetric flask
3.the solution is transfered to the flask and the last traces from a glass rod and beaker are rinsed with dissolved water
4.then the flask is filled drop at a time of distilled water until the bottom of the meniscus is exactly on the line
5.the volumetric flask is inverted to ensure the solution thoroughly mixed

Question 4

why do you invert the volumetric flask?

Answer 4

the mixing would be uneven. Inverting alows uniform mixing and an equal concentration throughout the solution

Question 5

whats the tolerance of the volumetric flask

Answer 5

100cm3 +- 0.2
250cm3 +- 0.3

Question 6

how to carry out a titration

Answer 6

1. fill a burette with acid of a known concentration
2. record the volume of acid in a burette
3. measure a known volume of alkali into a conical flask
   4.add a suitable indicator
   5.add acid from the burette to the conical flask slowly
   6.stop adding acid when the end point is reached
   7.record the volume of acid used
   8.repeat until you get concordant results within 0.1cm3
4. calculate the conc of alkali

Question 7

what are the three indicators

Answer 7

methyl orange: red in acid yellow in alkali
phenalthaline: colourless in acid pink in alkali
litmus: red acid blue in alkali

Question 8

mean titre is

Answer 8

within 0.1 ‘concordant’

if this is not taken into acount you loose accuracy of the titration

Question 9

what is the uncertainty of pipette of 20cm3 25cm3 and a burette of 50cm3?

Answer 9

pipette 10- +_ 0.04
pipette 25 +_ 0.06
burette +_ 0.1

Question 10

read from the ….. of the meniscus

Answer 10

bottom

Question 11

to make biurette readings more accurate

Answer 11

read to 0.05 not 0.1

Question 12

percentage uncertainty

Answer 12

100 x absolute uncertainty/calculated value