chapter 14 - volumetric analysis

Question 1

primary standard

Answer 1

• solid at room temp
• pure
• known formula
• store without deterioration
• high molar mass
• does not react with atmosphere

Question 2

preparing primary standard

Answer 2

1. weigh required mass
2. transfer to volumetric flask
3. half fill, swirl to dissolve
4. fill up to calibration line
5. invert to ensure even concentration

Question 3

volumetric pipette

Answer 3

• dispense known volume (aliquot)
• of standard solution
• rinse with water first
• then standard solution
• use pipette filler
• fill to calibration line

Question 4

burette

Answer 4

• dispense volume (titre) of unknown solution into aliquot
• graduated (initial - final)
• rinse process

Question 5

titration

Answer 5

• process to determine concentration of a reactant when the unknown solution is added from the burette to the known solution in the aliquot

Question 6

equivalence point

Answer 6

point at which the exact stoichiometric amount of acid/ base has been added to react with the acid/ base
(aim to stop here)

Question 7

endpoint

Answer 7

when the acid-base indicator changes colour
(indicator chosen so endpoint occurs right after equivalence point)

Question 8

indicators

Answer 8

• usually weak acid
• change colour when it changes from acid for to base form
• change colour at endpoint because base has reacted with all the acid in conical flask, so then the weak acid can react with the base.

Question 9

titration curves

Answer 9

shows:
- change in pH
- if aliquot was weak or strong acid/ base
- volume of titre
- pH at equivalence point
z shape

Question 10

choice of indicator

Answer 10

• each indicator has pH range which it will change colour
• must chose indicator that has a pH range within the straight section of titration graph

Question 11

acids and bases

Answer 11

strong acid + weak base
= equivalence point < 7
strong base + weak acid
= equivalence point >7

Question 12

random errors

Answer 12

attributed to the uncertainty in the equipment
- minimised by trials/ concordant titres
precision

Question 13

systematic errors

Answer 13

constantly gives reading/ effects results, same amount over/ under, constantly in one direction
result of method flaw, badly calibrated equipment, unexpected purity

Question 14

precision

Answer 14

very close to one another
effected by random errors

Question 15

accuracy

Answer 15

near the correct value
effected by systematic errors

Question 16

organic acids

Answer 16

• carboxylic acids are weak acids
• monoprotic (donate one H+)
• oxalic acid is diprotic

Question 17

organic bases

Answer 17

• amines are weak bases

Question 18

titration calculations

Answer 18

1. write balanced equation
2. determine volume of average titre
3. calculate mol of known using n=cv
4. use stoichiometry to calculate amount in mol of unknown substance
5. determine concentration of unknown using c= n/v