Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

3/4 CHEMISTRY > U4AOS1: analysis techniques II (chromatography & volumetric analysis) > Flashcards

U4AOS1: analysis techniques II (chromatography & volumetric analysis) Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

define volumetric analysis

A

an analytical technique where the principal measurement is volume - used to analyse solutions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

define gravimetric analysis

A

an analytical technique where the principal measurement is mass - use to analyse either solutions or solids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

define spectroscopy

A

an analytical technique where the principal measurement is light (electromagnetic radiation) intensity.

involves spectra/absorbance or transmission of specific wavelengths - analyse solutions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

define chromatography

A

an analytical technique that is used to separate substances present in a mixture - can detect the presence of a particular substance + sometimes conc of substance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

define wavelength

A

the distance between the same point on two successive waves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

define wavenumber

A

the number of waves present in a given distance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

define frequency

A

the number of waves that pass a given point in one second - HZ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is a primary standard

A

a substance whose amount in moles can be calculated accurately from their mass is called a primary standard

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what are the characteristics of a primary standard

A

-be readily obtainable in a pure form
-have a known chemical formula
-be easy to store (as solid or solution) without deteriorating or reacting with air
-have a high molar mass to minimise the effect of errors in weighing
-preferable be highly soluble and inexpensive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is the dilution factor

A

final volume/initial volume

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

substance in conical flask?

A

analyte
volume measured out by the pipette is called an aliquot

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

substance in burette?

A

other substance which is dispensed slowly into conical flask = titrant, and volume of solution delivered is the titre

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

equivalence point

A

the point during the titration when the solutions have reacted in exact mole ratios shown by the reaction equation // and when neither reactant is in excess

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

end point

A

observable point where indicator used in reaction changes colour so signal to stop titration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what should the burette and pipette be rinsed with?

A

with the acid or base being put into the equipment for titration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what should the volumetric and conical flask be rinsed with?

A

only with deionised water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what is a systematic error

A

it produces a constant bias in a measurement that cannot be eliminated by repeating the measurement eg. uncalibrated pipette

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what is a random error

A

they follow no regular pattern - unpredictable variations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

equivalence point in ____ acid vs ____ base pH curves

A
  1. strong acid vs strong base = usually 7
  2. strong acid vs weak base = less than 7 (closer to acid)
  3. weak acid vs strong base = greater than 7 (closer to base)
  4. weak acid vs weak base = X sudden change of pH, cannot determine proper equiv point
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what can rinsing the pipette or burette with deionised water result in?

A

dilution of the solutions, so may require less or more of the titre to neutralise the aliquot. concentration - changes accordingly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what doe all methods of chromatography have?

A

mobile phase
stationary phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what is adsorption?

A

refers to force of attraction where sample adheres to stationery voice.
stronger adsorption (eg. from polar sample attracted to polar stat phase) results in longer retention time

23
Q

what is desorption?

A

when a component is released from stationary phase and dissolves into the mobile phase = desorbing into mobile phase.
higher solubility in mobile phase = shorter retention time

24
Q

key words for chromatography?

A

Adsorb = stAtionary phase
desOrb = mObile phase

25
Q

how does HPLC work?

A

-HPLC - high performance liquid chromatography
-column = contains fine particle waxy solids, and high pressure required to help move substance through densely packed column.

26
Q

what does HPLC graphs show and measure?

A

-retention times can be used to compare w pure substances, so can identify compounds UNDER IDENTICAL CONDITIONS
-can measure peak area = determine concentration

27
Q

define retention time

A

the amount of time that a sample stays in the column.
samples have longer Rt is adsorb more strongly to stationary phase + bigger, so carried more slowly by mobile phase

28
Q

factors influencing retention times

A

-identity + composition of stationery phase
-identity + composition of mobile phase
-length of the column
-temperature of the column
-mobile phase flow rate
-surface area of the stationary phase (beads)

29
Q

what must you be careful of calibration curves?

A

-curve is only reliable for values that exist within range of values used = INTERPOLATION
-curve is unreliable to predict values outside range = EXTRAPOLATION

30
Q

what is the process of forming standard solutions?

A
  1. weigh the pure solid on an electronic balance
  2. transfer all to volum. flask using clean funnel
  3. rinse any remaining solid particles into the flask w/ deionised water
  4. half-fill the flask + stopper it, swirl to ensure solid particles dissolve
  5. add deionised water up to calibration line
  6. add stopper and shake to ensure even conc
31
Q

what range must concordant titres be in?

A

within 0.1 ml of each other

32
Q

what errors contribute to inaccuracies in titrations?

A

-using an unsuitable indicator
-contamination of sample
-not using concordant titres
-difficulty judging permanent change of colour (end point)
-changes in volume of sample
-difficulty in identifying reading on scale of burette

33
Q

uses of chromatography:

A
  1. separate compounds in mixture
  2. identify what compounds are present
    ALL UNDER IDENTICAL CONDITIONS
34
Q

why does separation occur in chromatography?

A

-different molecules have different speeds
-have different relative attractions to mobile and stationary phase
-so adsorb/desorb at different rates

35
Q

how to make HPLC more effective?

A

need to increase retention time bc achieve better separation and greater differences between peaks
-increase surface area
-increase length of column
-slower flow rate which is pumped through

measures absorbance of component and Rt

36
Q

why can you not conclude if the sample is present in the mixture from HPLC?

A

-different compounds may have the same retention time, so contribute to same peak
-not identical conditions used

37
Q

why do primary standards have high molar mass?

A

to allow for discrepancies in calculations, because mistakes relating to a bigger molar mass will have less of an impact.

38
Q

colour changes on oxidation of dichromate and permanganate

A

Cr2O7 2- = orange to green
MnO4- = purple to colourless

39
Q

table for effect on concetration

A

-alphabetical order
-arrows for Burette = point inwards
-arrows for Conical flask = point outwards

40
Q

how to calculate dilution factor?

A

bigger volume/smaller volume

eg. 10 mL diluted to 250 mL in volumetric flask, so dilution factor of 25

41
Q

does a weak monoprotic acid require less volume of a base than a strong monoprotic acid when both same concentration?

A

no. it requires the same amount of moles because they react in a 1:1 ratio

42
Q

density=

A

mass/volume

43
Q

state of carboxylic acids

A

aq

44
Q

how to careful with Rf valuses?

A

see if origin is at another number mark eg. starts at 2cm instead of actual 0

45
Q

how to work out dilution factor in chromatography?

A

area of largest peak (what they give you eg. espressor’s largest peak is 211 000 area) divided by actual largest peak in data (eg. caffeine’s largest peak was 19 000)

so, 211/19 = 11.10 -> need to round up so need to dilute by a minimum factor of 12

46
Q

how to work out dilution factor in chromatography?

A

area of largest peak (what they give you eg. espressor’s largest peak is 211 000 area) divided by actual largest peak in data (eg. caffeine’s largest peak was 19 000)

so, 211/19 = 11.10 -> need to round up so need to dilute by a minimum factor of 12

47
Q

what is key in chromotography?

A

all reactions, to be able to be compared, must be conducted UNDER IDENTICAL CONDITIONS

48
Q

how to measure retention time from HPLC chromatogram?

A

measure a line down from tip of peak to horizontal axis. eg. might be leaning a bit to the left, so leak tip is relevant

49
Q

what type of peak shape is O-H alcohol vs acid?

A

alcohol = rounded + deeper
acid = jagged points + weaker
N-H bonds usually have twin/vampire peaks

50
Q

describe with principles of chromatography why…

A

-differently sized molecules, polarities so different rates of movement
-different strengths of attraction of adsorbing to stationary phase and desorbing into mobile phase
-strongest adsorbance = travels least distance, and most soluble = greatest distance

51
Q

using calibration curves to determine concentration, is data accurately valid?

A

yes - conditions used in HPLC is consistent across all standards
yes - we could interpolate data as consistent for standard solutions of different concentrations
no - method is invalid bc not enough points were established from 0 to end point

52
Q

what could impact the accuracy of the results in titration reaction with MnO4-?

A

-error standardising solutions eg. KMnO4 sol
-there was another reductant other than the acid that was reacting with the substance

53
Q

density=

A

mass/volume

3/4 CHEMISTRY (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions