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CHEM 211 > Preliminary EX and Titration theory > Flashcards

Preliminary EX and Titration theory Flashcards

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1
Q

what are the 3 types of balances

A

Mettler, Denver and top loading

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2
Q

which balance is for approximate weighings

A

top loading

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3
Q

the sensitivity of a Mettler balance is

a) 10 mg
b) 0.1 mg
c) 0.01 mg

A

b

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4
Q

the sensitivity of a Denver balance is

a) 10 mg
b) 0.01 mg
c) 1 mg

A

c

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5
Q

the _____ has a max of 300g

A

Denver

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6
Q

the _____ has a max of 200g

A

Mettler

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7
Q

which of the balances has has the largest maximum

A

top loading with a 500-600 g max

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8
Q

true or false - the denver balance is used for small amounts

A

false - it is used for large amounts of liquids and corrosive substances

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9
Q

why does the beaker and sample have tp be dry before weighing on a analytical balance

A

because of evaporation that can cause a downwards drift or hygroscopic samples can absorb water and cause a upwards shift

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10
Q

what does a static charge to do a reading

A

it causes it to be erratic

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11
Q

true or false - the electronic balance compensates for the buoyancy effect

A

false - none of them do

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12
Q

true or false - denser materials are properly weighed but liquids will not be

A

true - liquids will be under weighed

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13
Q

what are the two forces that an object experiences in a fluid

A

gravimetric and buoyancy

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14
Q

we need to correct for buoyancy when weighing ___

A

liquids

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15
Q

how do we correct for buoyancy

A

m true - m obs x 1.0011

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16
Q

what are the steps for weighing on an analytical balance

A
  1. put on finger cots
  2. weigh container on analytical
  3. place on top loading and tare
  4. take off and add reagent
  5. put it back on top loading to weigh approx
  6. take to analytical to weight to 0.1 mg
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17
Q

list the 6 errors in weighing

A

open doors, hot beaker, wet beaker, static, fingerprints dirty balance and hygroscopic compounds

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18
Q

when do we use weighing by difference

A

for hygroscopic compounds and multiple weighings

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19
Q

what is the general procedure of weighing by difference for hygropscopic compounds

A
  1. zero analytical
  2. weigh reagent in bottle
  3. transfer reagent from bottle to beaker
  4. re weigh the reagent bottle
  5. W dispensed = W original reagent in bottle - W reagent left in bottle
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20
Q

weighing by ____ gives us n+1 weighings for n samples

A

difference

21
Q

is a Mohr pipet for high precision or not

A

it is less precise

22
Q

what is the formula for the volume delivered in a buret

A

pi x r^2 x L

23
Q

what temperature is calibrations for

A

20 degrees C

24
Q

random, non reproducible errors are called

A

indeterminate errors

25
Q

systematic, reproducible errors are called

A

determinate errors

26
Q

what kind of error comes from poor technique, no calibration, no correcting and poor design

A

determinate

27
Q

where are the errors distributed in indeterminate errors

A

around the mean value

28
Q

true or false - the determinate errors control the accuracy

A

true

29
Q

which error can be treated with statistical methods

A

indeterminate errors

30
Q

mean/median is less affected by outliers

A

median

31
Q

what is the precision of titrations

A

1 part per thousand

32
Q

true or false - titrations are based on stoichiometric reactions

A

true

33
Q

what is the equivalence point

A

mole of titrant = mol of analyte

34
Q

list the requirements for a titration reaction

A
  1. must be quantitatively complete
  2. must be fast
  3. stoichiometry must be known
  4. need to be able to determine equivalence point
35
Q

define a primary standard

A

it is used as a titrant or to standardize titrants ; its requirements are
1. high purity
2. low hygroscopicity
3. high solubility
4. high formula weight
5. atomospheric stability

36
Q

what is an example of a primary standard used as a titrant

A

AgNO3

37
Q

what is a secondary standard solution

A

it is a solution that is standardized against a primary standard

38
Q

what is an example of a secondary standard

A

EDTA or NaOH

39
Q

true or false - equivalence point will always represent the endpoint

A

false - not always

40
Q

_____ is the sudden change in physical property when analyte is fully consumed

A

endpoint

41
Q

what kind of an error is a titration error

A

systematic error

42
Q

how do you find the titration error

A

error = vol at endpoint - vol at equivalence point

43
Q

choose the correct titration

analyte and titrant react and we observe the endpoint volume

a) back titration
b) direct titration
c) blank titration

A

a

44
Q

describe the blank titration

A

same as direct, but a blank titration is also used (the blank includes everything used in the sample, except the sample itself)
- used to correct for indication error and impurities in buffer and reagents

45
Q

_____ is a titration of excess reagent

A

back titration

46
Q

in a back titration how do we know the moles of the reactant A

A

mol A = Total R added - mol product

47
Q

why would we do a back titration (4 reasons)

A
  1. rxn too slow
  2. side reactions
  3. not favourable equilibrium constant
  4. not able to get endpoint
48
Q

how do we find the endpoint in precipitation reactions

A
  1. fajans method
    - uses florescein as indicator
    - absorption when the charge of particles changes at equivalence point
    - uses direct titration
  2. Volhard method
    - back titration
    - ferric ion indicator
    - add excess silver, determine the excess content through a titration with SCN
49
Q

what is the primary standard used often to standardize NaOH or KOH

A

KHP (potassium hydrogen pthalate)

CHEM 211 (3 decks)

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