Brainscape's Knowledge GenomeTM

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


See full index

AH chem > 4 Researching Chemistry > Flashcards

4 Researching Chemistry Flashcards

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

what are precise results?

A

if experiments can be repeated several times and their values are numerically similar

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

what are repetable results?

A

if the same experimenter obtains these numerically similar values

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

what are reproducible results?

A

if a number of different experimenters obtain these numerically similar values

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

what is a systematic error?

A

an error repeated in each measurement made by the experimenter

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

what is a random error?

A

they are made by the experimenter

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

how can you reduce random errors in experiments?

A

repeated measurements and averaging

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

what are uncertainties?

A

uncertainty of measurements results from the scale or digital reading not being an exact or precise measurement

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

what is the equation for percentage error?

A

uncertainty/actual measurement made X 100

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

what are types of spectral data which can be organised?

A

absorption spectroscopy
mass spectroscopy
IR spectroscopy
portion NMR spectroscopy

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

why is a control experiment carried out?

A

to validate a technique or procedure is accurate

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

what does parts per million refer to?

A

1 mg per kg
or
1 mg per L

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

how many mg are in a kg?

A

1,000,000 mg = 1 kg

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

what is percentage by mass?

A

the mass of solute made up to 100cm3 of solution

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

what is percentage by volume?

A

the number of cm3 of solute made up to 100cm3 of solution

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

how is percentage by yield reduced?

A

mass transfer or mechanical losses
purification of product
side reactions taking place
equilibrium position

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

what can gravimetric analysis determine?

A

the mass of an element or compound in a substance

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

what are weighing boats?

A

used to measure substance on a balance without contamination

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

what is the function ‘tare’ on a balance used for?

A

allows the balance to be set to zero when an object is on top of the balance pan

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

what is weighing by difference?

A

the mass of an empty weighing boat is measured and the chemical is added to the boat and reweighed. the difference is the mass of the substance in the bottle.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is weighing accurately approximately?

A

weigh within the region of the calculated mass, but record exactly what you used

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

heating to a constant mass steps

A

the substance is initially weighed and recorded
the substance is heated to remove moisture
the substance is allowed to cool in a desiccator
the substance has its mass measured on a balance

repeating the steps of weighing, heating, cooling and reweighing until constant mass is obtained

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

what is the purpose of a desiccator?

A

prevents reabsorption of water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what is a constant mass?

A

the mass is no longer changing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what are two types of gravimetric analysis?

A

precipitation
volatilisation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

what qualities must a product have in order for precipitation and filtration to occur?

A

a low solubility so that all the product is precipitated
a particle size large enough for filtration
be stable at temperatures of 100-105 so it can dry in oven

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

how is precipitation and filtration carried out?

A

two solutions added together which form a solid
the filtrate is tested to ensure reaction has completed
filter the solid by heating to a constant mass
cool in a desiccator and weigh

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

how do you test to make sure a precipitation reaction has gone to completion?

A

add excess of one solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

how can you ensure a precipitation and filtration reaction is completed to a high standard through human action?

A

carry out with extreme care to ensure all material is transferred and all apparatus dried and weighed with extreme care

(any excess mass will change the calculation results)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

what happens during a volatillisation reaction?

A

the substance is heated and any volatile products (often water) are evaporated causing a loss in weight.
the substance is heated to a constant mass and the final mass is recorded.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

what is a standard solution?

A

a solution of accurately known concentration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

how can standard solutions be made?

A

weighing a primary standard accurately
dissolving in a small volume of solvent (usually deionised water)
solution is transferred with rinsings to a volumetric flask
make up to the graduation mark with water, stopper and invert.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

what is an alternative way to make a standard solution?

A

by accurate dilution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

how is accurate dilution carried out

A

pipette an appropriate volume of a standard solution into a volumetric flask
make up to the graduation mark with solvent (deionised water), stopper and invert

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

primary standard properties

A

high state of purity
stable when solid and in solution
soluble
reasonably high GFM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

examples of primary standards

A

sodium carbonate
hydrated oxalic acid
potassium hydrogen phthalate
silver nitrate
potassium iodate
potassium dichromate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

why can sodium hydroxide not be used as a primary standard?

A

relatively low GFM
unstable when solid as it absorbs moisture
unstable as a solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

what must you do to sodium hydroxide before using it in volumetric analysis?

A

standardise it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

what does standardising a solution do?

A

determines the exact concentration (molarity) of a solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

types of titrations

A

acid-base
redox
complexometric

40
Q

redox titration

A

occurs between oxidising and reducing agents

41
Q

complexometric titrations

A

based on reactions using complexometric reagents like EDTA to form complexes with metal ions to determine the concentration of metal ions

42
Q

what are back titrations?

A

they are used to find the number of moles of a substance by reacting it with an excess volume of a reactant of known concentration.

43
Q

when are back titrations carried out?

A

substance is a solid
substance has low solubility

44
Q

dilution factor equations

A

DF = final volume / initial volume
final concentration = initial concentration / DF

45
Q

colorimetry relationship

A

colour intensity of a solution and the concentration of the coloured species present

46
Q

how do you know if a solution is coloured?

A

it absorbs some but not all parts of white light passing through it

47
Q

what happens to the parts of white light which isn’t absorbed in colourimetry?

A

they are transmitted through the solution and combine to give the colour we see

48
Q

how do you know what colour will be absorbed in colorimetry?

A

the complementary colour of the colour we can see

49
Q

what does the intensity of the colour in colorimetry depend on?

A

the concentration of the solution

the more concentrated - the darker the colour

50
Q

what is used to measure the absorbance of light of a series of standard solutions?

A

colorimeter
spectrophotometer

51
Q

describe a cuvette

A

it is where the coloured samples are placed in a colorimeter
one side is clear and faces the light source
other side is ribbed and is used to pick up/down

52
Q

what is the first step of analysing a compounds absorbance?

A

a reference or blank sample (normally distilled water) is analysed

53
Q

what value should a blank give in colorimetry?

A

0

54
Q

how do you decide the colour of the filter in colorimetry?

A

it should be complementary to the colour of the solution being analysed

55
Q

how do you find the value of the absorbance for a sample in colorimetry after the experiment has occurred?

A

the difference between the absorbance of the coloured solution and the blank

56
Q

what is needed in order to create a calibration graph?

A

a series of standard solutions prepared at different concentrations

measure their absorbance and plot it on the graph

57
Q

what is essential when carrying out a calibration graph?

A

the concentration of the coloured species being tested must lie within the straight line section

58
Q

what is distillation?

A

identifies and purifies organic compoundsh

59
Q

how does distillation identify the substance being tested?

A

it can determine its melting point

60
Q

how can distillation purify the substance being tested?

A

it can separate the substance form less volatile substances in the mixture

61
Q

what is reflux?

A

a technique used to apply heat energy to a chemical reaction mixture over an extended period of time without volatile substances escaping

62
Q

how is reflux set up?
draw diagram

A

liquid reaction mixture placed in a round bottom flask along with anti-bumping granules with a condenser at the top

check diagram

63
Q

how is distillation set up?
draw diagram

A

check diagram

64
Q

how does reflux work?

A

the flask is heated vigorously over the course of the reaction. any vapours which are given off are immediately returned to the reaction as liquids when they reach the condenser

65
Q

what type of flasks does vacuum filtration use?

A

buchner
hirsch
sintered glass funnel

66
Q

what does vacuum filtration do?

A

they are carried out under reduced pressure and provides a faster means of separating the precipitate from the filtrate

67
Q

how do you choose an appropriate filter medium for vacuum filtration?

A

depends on the quantity and nature of the precipitate

68
Q

what is recrystallisation?

A

used to purify solids

69
Q

recrystallisation steps

A

the impure compound is dissolved gently in the minimum volume of hot solvent
hot filtration occurs to remove any insoluble impurities
the filtrate is allowed to cool slowly to allow crystals of the pure compound to form, leaving soluble impurities dissolved in the solvent
the crystals are isolated by filtration, washing with cold water and drying the pure crystals

70
Q

conditions of the impure compound when choosing a solvent for recrystallisation

A

soluble at high temperatures
insoluble at lower temperatures

71
Q

solvent qualities when choosing a solvent for recrystallisation

A

immiscible with the liquid or solution (usually water)
one in which the solute is more soluble in than the liquid mixture or solution
volatile to allow the solute to be obtained by evaporation of the solvent
unreactive with the solute

72
Q

what does immiscible mean?

A

incapable of mixing

73
Q

when do you use solvent extraction?

A

if the desired product is present in an aqueous mixture (water is in the solvent)

74
Q

properties of the 2nd solvent in solvent extraction

A

must be immiscible with water (non-polar)
the solute is more soluble than water
volatile to allow the solute to be obtained by evaporation of the solvent
unreactive with the solvent

75
Q

how does solvent extraction work?

A

ageous mixture and non-polar solvent are all placed in the funnel and vigorously shaken for several minutes
the desired product moves to the non-polar solvent
it is then ‘ran off’ from the funnel and collected
solvent evaporated leaving a pure sample

76
Q

equipment used in solvent extraction

A

separating funnel

77
Q

why is solvent extraction repeated?

A

to maximise the quantity of solute extracted

78
Q

what is good practice in a solvent extraction?

A

using smaller volumes of the chosen solvent
if 50cm3 available - do two using 25cm3

79
Q

how does equilibrium work in solvent extraction?

A

the desired product distributes itself between two layers which sets up an equilibrium
the concentration of the solute can be determined in both layers and the equilibrium constant K calculated

80
Q

what is a the melting point of a substance?

A

the temperature range over which the solid first starts to melt, to when all of the solid has melted

81
Q

how do you know if your compound is pure when finding its melting point?

A

it can be confirmed by comparing the experimentally determined melting point with a literature or known mp value

82
Q

how does impurities effect a mp?

A

broades and lowers
caused by disruption in intermolecular bonding in the crystal lattice

83
Q

what does mixing a pure product and some of your own product together do in mp determination?

A

mp value and the range of the melting temperature can be used to determine if the product and pure compound are the same substance.

84
Q

what is chromatography and what does it use to do its purpose?

A

separates non-volatile components present within a mixture
it does this by using the differences in their polarity or molecular size

85
Q

how is TLC set up?

A

it is performed on a sheet of glass, plastic or aluminium foil which is coated in a thin layer of absorbent material usually silica gel or aluminium oxide

86
Q

stationary phase of TLC

A

the solid plate

87
Q

mobile phase TLC

A

liquid (solvent)

88
Q

how does the substance travel up the plate in TLC?

A

the more strongly a component of a mixture is absorbed onto the stationary phase, the less time it will spend in the mobile phase and the more slowly it will migrate up the plate

89
Q

what does the distance the compounds carry depend on in TLC?

A

how soluble the compounds are in the chosen solvent

how well they adhere to the plate

90
Q

what do you do if your spots don’t show up on your TLC plate?

A

a developing agent or ultraviolet light in required

91
Q

how to calculate Rf value?

A

distance travelled by the sample / distance travelled by the solvent

92
Q

will a compounds Rf value ever change?

A

not if the conditions are kept the same and within experimental error
(temp, solvent, saturation levels)

93
Q

how can you identify a compound using TLC?

A

compare the experimentally determined Rf value with literature values determined under the same conditions

make a direct comparison on a TLC plate between the compound being tested and the pure substance where a co-spot has been used

94
Q

how does TLC identify the purity a the substance?

A

a pure substance should appear as a single spot when developed

95
Q

what does the presence of multiple spots on a TLC plate show?

A

impurities are present

AH chem (4 decks)

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