Titrations

Question 1

Titration

1

Answer 1

laboratory technique used to determine [unknown solution] by reacting it with solution of known conc

Question 2

Volumetric analysis

1

Answer 2

chemical analysis involving calc of volumes

Question 3

Standardisation

1

Answer 3

volumetric analysis to determine the conc of a solution

Question 4

Equivalence point

1

Answer 4

point at which equal stoichiometric amounts of each solution have reacted

Question 5

End point

1

Answer 5

pH at which indicator changes colour

Question 6

Indicator def

1

Answer 6

an organic weak acid/base conjugate pair with distrinct colours that change colour based on surrounding pH

Question 7

Methyl orange

Answer 7

acidic range
(red in acidic - yellow in basic)

Question 8

Phenolphthanlein

Answer 8

basic range
(colourless in acidic - pink in basic)

Question 9

Methyl red

Answer 9

neutral range

Question 10

Random error

1

Answer 10

even chance of the result being higher or lower than the true value each time → inconsistent effect

Question 11

What might cause random errors in titrations

2

Answer 11

• taking a measurement
• incorrect judgement of colour change

Question 12

How to reduce random error

1

Answer 12

average trials

Question 14

Systematic error

1

Answer 14

consistently affect results so that they are always higher/lower than true value

Question 15

What might cause systematic error

2

Answer 15

• using incorrect indicator
• incorrect rinsing procedures

Question 16

E.g. add phenolphthalein to HCl + Na2CO3

2 - explanation

Answer 16

• average volume of HCl will be less than that required to reach equivalence point
• calculated [HCl] is greater than the actual value

Question 17

Analytical balance use

1

Answer 17

measures accurate masses of solids used to make up standard solution

Question 18

Pipette use

1

Answer 18

Accurately delivers specific measured volume (aliquot)

Question 19

Pipette rinsing procedure

1

Answer 19

Rinse with small amount of solution being delivered prior to use

Question 20

Burette use

1

Answer 20

Accurately delivers a variable volume (titre)

Question 21

Burette rinsing procedure

1

Answer 21

Rinse with small amount of solution being delivered prior to use
adding water will dilute it

Question 22

Volumetric flask use

1

Answer 22

Holds accurately known volume of solution used to make up standard solution

Question 23

Volumetric flask rinsing procedure

Answer 23

Rinse with distilled water prior to use

Question 24

Conical flask use

Answer 24

Used to hold reaction mixture during titration

Question 25

Conical flask rinsing procedure

Answer 25

Rinse with distilled water prior to use bc doesn’t effect moles of base/acid

Question 26

Standard solution | 1

Answer 26

has a known conc

Question 27

What are suitable primary standards | 2

Answer 27

- anhydrous Na2CO3 - oxalic acid

Question 28

Features of primary standard | 5

Answer 28

- known formula and can be obtained with a high degree of purity - don’t react with gases in atmosphere (CO2 & O2) - doesn’t absorb/release H2O to/from the atmosphere - high Molar Mass - minimise error - dissolve readily in water to form a stable solution

Question 29

Deliquescent

Answer 29

absorbs a lot of H2O (NaOH)

Question 30

Hydroscopic

Answer 30

absorbs H2O from atmosphere (HCl)

Question 31

Efflorescent

Answer 31

release H2O to atmosphere (Na2CO3.10H2O)

Question 32

Why can't HCl be used as a primary standard | 2

Answer 32

- it’s a gas → hard to measure - volatile (easily changes to gas)

Question 33

Secondary standard solution | 2

Answer 33

solution of known conc by titration with another standard solution e.g. HCl, NaOH