U4AOS1: analysis techniques II (chromatography & volumetric analysis)

Question 1

define volumetric analysis

Answer 1

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

Question 2

define gravimetric analysis

Answer 2

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

Question 3

define spectroscopy

Answer 3

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

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

Question 4

define chromatography

Answer 4

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

Question 5

define wavelength

Answer 5

the distance between the same point on two successive waves

Question 6

define wavenumber

Answer 6

the number of waves present in a given distance

Question 7

define frequency

Answer 7

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

Question 8

what is a primary standard

Answer 8

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

Question 9

what are the characteristics of a primary standard

Answer 9

-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

Question 10

what is the dilution factor

Answer 10

final volume/initial volume

Question 11

substance in conical flask?

Answer 11

analyte
volume measured out by the pipette is called an aliquot

Question 12

substance in burette?

Answer 12

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

Question 13

equivalence point

Answer 13

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

Question 14

end point

Answer 14

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

Question 15

what should the burette and pipette be rinsed with?

Answer 15

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

Question 16

what should the volumetric and conical flask be rinsed with?

Answer 16

only with deionised water

Question 17

what is a systematic error

Answer 17

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

Question 18

what is a random error

Answer 18

they follow no regular pattern - unpredictable variations

Question 19

equivalence point in ____ acid vs ____ base pH curves

Answer 19

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

Question 20

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

Answer 20

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

Question 21

what doe all methods of chromatography have?

Answer 21

mobile phase
stationary phase

Question 22

what is adsorption?

Answer 22

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

Question 23

what is desorption?

Answer 23

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

Question 24

key words for chromatography?

Answer 24

Adsorb = stAtionary phase
desOrb = mObile phase

Question 25

how does HPLC work?

Answer 25

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

Question 26

what does HPLC graphs show and measure?

Answer 26

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

Question 27

define retention time

Answer 27

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

Question 28

factors influencing retention times

Answer 28

-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)

Question 29

what must you be careful of calibration curves?

Answer 29

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

Question 30

what is the process of forming standard solutions?

Answer 30

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

Question 31

what range must concordant titres be in?

Answer 31

within 0.1 ml of each other

Question 32

what errors contribute to inaccuracies in titrations?

Answer 32

-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

Question 33

uses of chromatography:

Answer 33

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

Question 34

why does separation occur in chromatography?

Answer 34

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

Question 35

how to make HPLC more effective?

Answer 35

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

Question 36

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

Answer 36

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

Question 37

why do primary standards have high molar mass?

Answer 37

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

Question 38

colour changes on oxidation of dichromate and permanganate

Answer 38

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

Question 39

table for effect on concetration

Answer 39

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

Question 40

how to calculate dilution factor?

Answer 40

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

Question 41

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

Answer 41

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

Question 42

density=

Answer 42

mass/volume

Question 43

state of carboxylic acids

Answer 43

aq

Question 44

how to careful with Rf valuses?

Answer 44

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

Question 45

how to work out dilution factor in chromatography?

Answer 45

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

Question 46

how to work out dilution factor in chromatography?

Answer 46

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

Question 47

what is key in chromotography?

Answer 47

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

Question 48

how to measure retention time from HPLC chromatogram?

Answer 48

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

Question 49

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

Answer 49

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

Question 50

describe with principles of chromatography why...

Answer 50

-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

Question 51

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

Answer 51

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

Question 52

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

Answer 52

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

Question 53

density=

Answer 53

mass/volume