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Analytical chemistry Flashcards

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1
Q

m/z=91?

A

X c6h5ch2

Correct: C6H5CH2+

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2
Q

volumetric analysis condition

A
  1. significant change can easily be detected with the complete consumption of the reagent in the conical flask eg indicator
  2. reaction must be significantly complete (not eqm
  3. rate of reaction must be fast enough
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3
Q

why I2 need to be freshly produced

A

I2 is volatile

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4
Q

why heat is used in a reaction

A

to ensure the reaction go to completion

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5
Q

determine octane in petrol

A

gas chromatography-mass spectrometry

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6
Q

why blue filter s used in colorimetry for Cr2O7

A

Orange Cr2O72- solution absorb blue light to a large extent

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7
Q

MnO4- + Fe2+ to Mn2+ + Fe3+ endpt color change?

A

pale yellow to pale pink

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8
Q

how to purify substance after distillation

A

column chromatography

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9
Q

how to make up to 250cm3 solution

A

poor to 250cm3 volumetric flask

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10
Q

condition of liquid-liquid extraction

A

the organic solvent should be immiscible with water and with lower boiling point

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11
Q

how to separate NH4Cl

A

sublimes when heated with inverted funnel

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12
Q

why NaOH cant be prepared by dissolving

A

absorb water

reacts with CO2 at atmosphere

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13
Q

how to distinguish MgSO4 and MgSO4.7H2O

A

heat in a test tube
place a dry CoCl2 paper on the tube
turn paper from blue to pink

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14
Q

process of crystallistion

A

dissolve sample in water
filter off any impurities
heat the filtrate until it becomes saturated
allow solution cool down to crystalline
filter off the crystals
rince the crystals with cold distilled water
dry crystal by filter paper

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15
Q

what is the most suitable drying agent for NH3

A

anhydrous calcium oxide (no chemical reaction)

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16
Q

How to obtain pure Zinc in (Zn(NH3)4)2+

A

Acidify the solution with acid
Add excess Na2CO3
Heat ZnCO3 strongly with C

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17
Q

precaution when using tollens’ reagent

A

wear hand gloves as Ag+ is toxic and turns our skin brown.

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18
Q

observation of the measurement of the m.p. of a inpure substance

A

the samples melts gradually over a wide temperature range

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19
Q

observation of the analysis of an inpure substance by thin layer chromatography

A

more than one spot will be observed in the chromatographic plate obtained.

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20
Q

how to remove NH4Cl from a mixture of NH4Cl and NaCl

A

Heating the sample

Nh4Cl sublimes to NH3 and HCl on heating

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21
Q

how to improve the efficiency of separation in fractional distillation

A

use a longer fractionating column

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22
Q

why AgNO3 is not suitable for primary standard

A

It is light-sensitive

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23
Q

why starch indicator is only added near the end point

A

I2 forms a stable complex with starch

Early addition of starch will affect the accuracy of the end-pt

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24
Q

what is a primary standard

A

A primary standard is a reagent used to prepare a solution of known molarity. The solution is prepared by direct weighing a known amount of the reagent and dissolving it in a known volume of solution.

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25
Q

how to accurately record the water level

A

read the upper part of the meniscus level.

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26
Q

source of formaldehyde in a newly furnished home

A

urea-formaldehyde which is used as adhesive or coating material

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27
Q

define Rf value

A

Rf value is defined as the ratio of the distance traveled by the center of a component spot to the distance traveled by the solvent front.

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28
Q

why excess dilute HNO3 is added to the AgNO3 before test

A

To prevent the formation of solid such as Ag2CO3, Ag2SO3 as it can form precipitate with them.

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29
Q

why chromatography is used to seperate a mixture

A

Because different substance have different adsorptivity to the stationary phase and different solubility in mobile phase

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30
Q

how to describe the peak in a mass spectra

A

significant peak at m/z=

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31
Q

why direct titration between ascorbic acid and iodine solution is not preferred

A

iodine solution is not stable in air

reaction rate between ascorbic acid and iodine is slow

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32
Q

why a redox titration is better than acid alkali solution in determining the amount of ascorbic acid in the orange juice sample

A

orange juice contains other acids and so the result of acid alkali titration shows the total amount of acids in the sample(not only ascorbic acid)

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33
Q

why the glass bottle should be capped in TLC

A

to ensure that the glass bottle is saturated with the solvent vapour

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34
Q

what is qualitative analysis

A

determination of the identity of a chemical species

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35
Q

what is quantitaitve analysis

A

determination of how much a chemical species is present

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36
Q

is Ba(OH)2 soluble in water

A

yes

it is a strong alkali

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37
Q

Ca2+ react with NaOH to form Ca(OH)2 but cant react with NH3 to form Ca(OH)2

A

its becuase Ca(OH)2 is slightly soluble
while NH3 is a weak alkali
so conc of OH- is not enough to form Ca(OH)2

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38
Q

suggest a common use of compounds of group 1 and 2 metals

A

fireworks

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39
Q

what will be observed when a flame test is conducted with Mg2+ ion

A

no characteristic flame!!

only burning Mg ribbon cause bright white flame
ions cant

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40
Q

what is the smell of H2S

A

bad egg smell

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41
Q

CuSO4.nH20

n usually =?

A

5

42
Q

what is the bleaching action of SO3 2-

A

SO3 2- + dye –> SO4 2- + (dye-O)

43
Q

is AgCl soluble in conc NH3

A

yes

Br2 –> slightly soluble only
I2 –> insoluble

44
Q

test for SO4 2-

A

add acidified BaCl2

white precipitate formed

45
Q

how to distinguish Na2CO3 and NaHCO3

A

add MgCl2
CO3 2- will form white preicipate
while HCO3 - wont

46
Q

how to distinguish S2O3 2- ion

A 
add acid (HCl /H2SO4)
turns cloudy with the formation of yellow solid (sulphur)
47
Q

what is the general precaution dealing with explosive , flammable and oxidizing substances

A

keep away from heat and naked flame

48
Q

is Tollens’ reagent OA or RA

A

OA
it reduces to Ag (silver mirror)
and oxidize aldehyde to carboxylates (COO-)

49
Q

how to distinguish amide

A

boil with NaOH

NH3 form which turns moist red litmus paper blue

50
Q

how to write the observation when aldehyde is tested by Tollens’ reagent

A

silver mirror is formed on the wall of test tube

51
Q

what is the solid-liquid mixture called

A

suspension

52
Q

why crystals form when colling a hot saturated solution

A

the solubility of most solids decrease with decreasing temperature

53
Q

why rapid filtration is needed when removing insoluble impurities during recrystallization

and how to do so?

A

it is because it is necessary to avoid recrystallization during filtration in this step

use suction filtration by Buchner funnel to increase the speed of filtration

54
Q

why the filter paper should be fluted

A

to increase surface area for filtration

55
Q

why stemless funnel should be used during recrystallisation

A

to avoid recrystallization inside the stem

56
Q

should we extract a chemical with one portion of solvent or with several smaller portions in liquid-liquid extraction

A

it is more efficient to extract a solute with several smaller portions of solvent than with one portion of solvent, although the total volume of solvent used is the same

57
Q

what is the use of the fractionating column

A

it provides a large surface area for repeated condensation and vapourization of the mixture to occur

58
Q

what is the reverse of sublimation

A

deposition

59
Q

name in the paper chromatography

A

starting line
sample spot
solvent front
cover

60
Q

how to observe spot with amino acid on a chromatogram

A

spray ninhydrin

purple spots can be seen

61
Q

how to observe spot with organic colorless compound on a chromatogram

A

standing the chromatogram in a container saturated with iodine vapor
the iodine vapor will combine with the organic compound which results in a brown spot

62
Q

what is Rf value

A

it is the ratio of distance moved by the spot to the distance moved by the solvent front from the baseline

63
Q

describe the principle of paper chromatography

A

paper chromatography consists of a stationary phase and a mobile phase which is the solvent
different components in a mixture have different degrees of adsorption to the stationary phase and different solubilities in the mobile phase
the component which is more soluble in the solvent or adsorb less to the stationary phase will move more rapidly with the solvent
so, the components can be seperated

64
Q

what does the mobile phase called in column chromatography

A

eluent

the process is called elution

65
Q

how to test for the purity of a subtance

A

if a substance is pure, it melts or boils at a precisely defined temperature
it has a very sharp melting and boiling point

66
Q

what will the melting point and boiling point be if a substance is impure

A

impure substance usually has a lower melting point but a higher boiling point

67
Q

why some people spread sodium chloride on highway after a heavy snow

A

add salt to ice can lower the melting point of ice, so ice melt below its normal melting point and help remove ice on the road surface

68
Q

what is the requirement of primary standard

A

highly pure
stable in air
should not absorb water an CO2 in air
should be soluble in water

primary standard is a substance that can be used to prepare a standard solution without standardization

69
Q

why conc H2SO4 and NaOH is unsuitable for preparing standard solution

A

they absorb water

70
Q

why NH3 is unsuitable for preparing standard solution

A

it is very volatile

71
Q

which methods is more accurate?

titration or measuring conductivity

A

titrimetric method is more accurate
as the end-point of acid base titration is sharp and easily observable
besides experimental errors, there are also errors in plotting and extrapolating graphs in conductometric method

72
Q

why I2 cannot prepare a standard solution

A

I2 is volatile

its difficult to weigh accurately a sample of I2

73
Q

why starch should be add at the later stage of the titration

A

starch irreversibly combines with iodine at a high conc. of I2 so that I2 will not be released from starch at the end point

74
Q

when should starch solution be added in the I2 S2O3 2- titration

A

when the color change from brown to pale yellow

75
Q

why KMnO4 solution cannot be prepared by dissolving a known mass of KMnO4 in water

A

it is because KMnO4 cannot be obtained in highly pure form as it decomposes to give MnO2 easily in air
the aqueous solution of KMnO4 is unstable
it should be stored in a brown bottle

76
Q

what is the end-pt color change of the reaction between permanganate and iron(ii)

A

pale yellow to pink

77
Q

for better quality of water

the permanganate index should be smaller or larger?

A

smaller

less POTASSIUM permanganate required to oxidize all reducing agent in the water

78
Q

what is the indicator in Mohr’s method

A

Na2CrO4

reddish brown precipitate formed (formation of Ag2CrO4 after AgCl)

79
Q

what is color intensity directly proportional to?

A

concentration of the solution

80
Q

what are the limitations on using colorimetry

A

the sample must be in solution form
the sample should be colored
the sample should not be a mixture of substance with similar colors

81
Q

explain whether volumetric analysis or colorimetry is more appropriate in determining the concentration of a very dilute solution

A

colorimetry is more appropriate as the low color intensity of the solution can still be determined by colorimetry

82
Q

what is infrared spectroscopy

A

it is the method using the infrared spectrometer to analyze the covalent bonds present in a covalent compound

83
Q

what is an infrared spectrum

A

it is a graph of transmittance against wavenumber

84
Q

when will the frequency of vibration increase

A

mass of atom decrease

bond strength increase

85
Q

why the presence of intermolecular H-bonds in the sample produces a broad band

A

the vibration is complicated by H-bond formed between the molecules

86
Q

limitation of IR spectroscopy

A

peaks always overlap
intermolecular interactions between molecules can result in complicated infrared spectra
not all vibration give rise to strong absorption peak

87
Q

uses of mass spectrometry

A

determine relative molecular mass
determine composition of a mixture
determine the structures of organic compound

88
Q

what are the procedures of mass spectrometer

A 
vaporization
ionization
acceleration
deflection
detection
89
Q

why sample need to be ionized

A

to form positive ions (molecular ions)

90
Q

what is a nass spectrum

A

a graph of relative intensity against m/e ratio

91
Q

how a positive ion is formed in mass spectrometer

A

In the ionization chamber, AB3 molecules were bombarded by fast moving electrons.
This leads to knocking out of an electron from a AB3 molecule to give AB3+

92
Q

what does base peak means

A

it is the most intense peak which represents the most stable or abundant ion

93
Q

what does molecular ion peak means

A

the peak with the relative molecular mass

94
Q

sources of CO

A

incomplete combustions of fossil fuels in car engines

95
Q

negative impact of CO

A

it decrease the oxygen carrying capacity f haemoglobin, causing dizziness or even death

96
Q

what are the source of formaldehyde

A

furniture made of wood products with formaldehyde-based adhesive

97
Q

hazard of formaldehyde

A

toxic and carcinogenic

it causes burning and watery eyes or even trigger asthma symnptoms

98
Q

what can be done to identify fingerprints

A

iodine sublimation

99
Q

how to prevent fading of the brown fingerprint

A

spray starch solution

100
Q

why bromine liquid is not suitable to be a primary standard

A

Br liquid is volatile

101
Q

propanone is…

A

flammable

chem (14 decks)

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