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Chemistry > Missed Questions > Flashcards

Missed Questions Flashcards

1
Q

how does the structure of DNA enable the primary structure of a protein

A

The sequence of bases in DNA determines the primary structure of proteins synthesized by the cell using a triplet code, known as the genetic code, which is universal.

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2
Q

importance of cholesterol in the diet

A
  1. important for helping food pass through the intestines by adding dietary fibre
  2. helps prevent obesity
  3. helps prevent constipation
  4. reduces risk of IBS
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3
Q

treatment for carbon monoxide poisoning

A
  1. exposure to high pressure O2 chamber
  2. moving patient to fresh air
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4
Q

outline how you a solution of 0.0100moldm^-3 is obtained from a standard 1.000moldm^-3 naming two essential pieces of glassware

A
  1. volumtric flask
  2. volumetric pipette
  3. make up a solution that is 1/100 concentration; e.g. 5cm^3 of the 1.000 moldm^-3 standard made up to 500cm^3 solution with distilled water
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5
Q

why does graphene have a smaller bond length than diamond

A

it has sp2 hybridization and is only bonded to 3 other carbons, so the fourth electron is delocalized and can form partial double bonds, which makes the bond order 4/3 (1.333)

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6
Q

why does graphene have a higher melting point than diamond

A

the carbons in graphene have shorter bond lengths than the carbons in diamond, and shorter bonds are stronger and thus require more energy to overcome

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7
Q

what happens when covalent molecules are melted (differentiate between giant covalent and normal covalent molecules)

A

in covalent molecules, the covalent bonds are not being broken apart, rather, it is the intermolecular forces between them that are being overcome. by contrast, in giant covalent molecules, it is normally the actual covalent bonds in the molecule that must be broken apart for the molecule to melt

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8
Q

outline one impact food labelling has had on the consumption of foods containing different types of lipids

A

it has affected consumption of trans fats and cis trans fats and unsaturated fats as unsaturated fat consumption is increasing and saturated fat consumption, and reduction of saturated fats

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9
Q

justify why it is inappropriate to record the uncertainty of the mean (time) as +- 0.01s

A

because the uncertainty does not take into account human errors

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10
Q

state giving a reason why something is a systematic error

A

it is an error within the methodology, more repetitions would not reduce the error,

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11
Q

state the name of the process used to break down the insulin protein into its constituent amino acids

A

hydrolysis

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12
Q

identify the type of rancidity that occurs in saturated lipids and the structural feature that causes it

A

ester groups are susceptible to hydrolytic rancidity

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13
Q

outline how amino acids may be identified from a paper chromatogram

A

Rf values compared with known amino acid

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14
Q

omega 3 fatty acid benefits

A

reduces risk of CHD, important for adolescent brain development (helps build cell membranes in the brain)

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15
Q

outline why cellulose fibers are strong

A

rigid structure, long straight/unbranched chains, multiple hydrogen bonds between chains

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16
Q

state 3 features of dynamic equilibrium

A
  1. occurs in a closed system
  2. rate of forwards and backwards reactions are the same
  3. concentrations of reactants and products are constant
  4. there is no change to macroscopic properties
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17
Q

why are oxides of phosphorus not major contributors to acid deposition

A

phosphorus is not commonly found in fuels

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18
Q

outline one precombustion method and one post combustion method

A

pre-combustion: removal of sulfur/desulfurization
post-combustion: removal by neutralization/ reacting with an alkali

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19
Q

advantages of using starch for plastics

A

biodegradable, does not contribute to landfill, lower greenhouse gas emissions, less energy needed for production, renewable

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20
Q

disadv of starch for plastics

A

growing corn for plastics instead of food, poor mechanical strength, cannot be reused, starch breakdown can produce methane, increased use of fertilizers has negative environmental impacts

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21
Q

how to name an amino acid using IUPAC rules

A

2-amino- #methyl[prefix]anoic acid

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22
Q

justify why this molecule is a carbohydrate

A

it has the formula Cx(H2O)Y, both contain several OH groups and C=O carbonyl groups

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23
Q

why might a crucible turn black after heating

A

soot due to incomplete combustion, which can cause the mass to be greater

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24
Q

suggest that assumptions that are being made when a hydrous compound is being heated to make it anhydrous

A

any changes in mass are due tot he loss of water, the compound contains no impurities, the crucible does not absorb or lose water

25
Q

suggest why the melting point of vanadium is higher than that of titanium

A

vanadium has one more proton than titanium, so it has a stronger positively charged nucleus and a SMALLER IONIC RADIUS

26
Q

explain why an aluminium titanium alloy is harder than pure aluminium

A
  1. the metals are different sizes which alters the regular packing of the metal ions AND
  2. prevents the layers from sliding over each other
27
Q

how would you determine the appropriate indicator for a reaction between a weak base and dilute sulfuric acid

A

the concentration of sulfuric acid doesn’t matter because it is still a strong acid, so you would pick one that would match with the curve for a strong acid with weak base

28
Q

explain why TMS is often used as a reference standard in H NMR

A

very volatile, inert so it will not react with the sample, produces a strong chemical shift of 0ppm so it can be used for a reference

29
Q

state the reagents used in the two-stage conversion of nitrobenzene to aniline

A
  1. conc. HCl and Sn to produce a phenylammonium ion
  2. NaOH (aqueous) to remove an H+ to form the amine group
30
Q

what is the equation that can be used to demonstrate the catalysis of ozone destruction

A

NO* + O3 -> XO* + O2
NO2* + O3 -> NO* +2O2

31
Q

resonance structure

A

several possible positions for a double bond

32
Q

how would you describe a delocalized pi bond across several atoms

A

delocalized pi bond extending over the (X) atom and (Y) atom

33
Q

physical evidence for structure of benzene

A

all bond angles are the same, all bond lengths of benzene are the same

34
Q

what does NaOH act as when it is in an alcoholic solution versus in an aqueous solution

A

acts as a base by accepting a proton versus acting as a nucleophile

35
Q

why is the loss of ozone an international environmental concern

A

loss of ozone allows UV radiation to penetrate the atmosphere and can cause skin cancer and damage to the skin

36
Q

outline hydrolytic rancidity

A
  1. caused when ester bonds in the lipid are hydrolyzed when foods are exposed to water
  2. factors that increase hydrolytic rancidity: enzymes, organic acids, elevated temperatures
  3. ways to reduce hydrolytic rancidity: store food at lower temps, reduce water content
37
Q

outline oxidative rancidity

A

C=C double bonds broken by free radical oxidation in reactions with molecular oxygen
- sunlight increases oxidative rancidity
reduce via: light proof packaging, addition of food additives

38
Q

any questions about vitamin a and its role in the visual cycle

A
  1. vitamin has extensive delocalization
  2. vitamin a is oxidized to cis retinal
  3. cis-retinal binds to opsin to form rhodopsin protein. rhodopsin extends the conjugation and allows absorption of visible light
  4. cis retinal converts into the trans form when visible light is absorbed
  5. 11- trans retinal no longer fits into the rhodopsin protein and is ejected leading to a conformational change in the shape of rhodopsin
  6. trans-retinal is converted back to cis-retinal through enzyme activity
  7. this leads to opsin generating a signal
39
Q

what is a source of error/uncertainty that should be included when a stop watch is used

A

the uncertainty of the student’s reaction times

40
Q

explain why the blue color of a quinoidal base changes to the red color of a flavylium

A

as the pH decreases, there are more protons in solution, so the quinoidal base is protonated; this results in a corresponding electron shift which decreases the electron density and subsequently the extent of conjugation in the backbone, which results in shorter wavelength light to be absorbed as a result of increases in the energy of e- transitions, so the observed color becomes more red

41
Q

how did the enthalpy of hydration of benzene disprove kebules structure

A

it was less exothermic than expected because it has delocalized e- instead of alternating single and double bonds which makes it more stable, meaning that it has lower energy, so there is less of an energy gap than there would have been if the molecule had alternating bonds and was more unstable with higher energy

42
Q

how does the presence of a precipitate affect the measurement of the endpoint of a titration

A

precipitate formation makes it difficult for the color change to be seen

43
Q

how does dilution affect the rate of reaction

A

dilution lowers the concentration of the reactant particles which reduces the frquency of successful collisions between particles and hence causes rate to decrease

44
Q

two reasons that the enthalpy change from formation data and bond enthalpy data are different

A
  1. bond enthalpy data assumes that all of the reactants and products are gaseous, but formation data takes into account that one of the products is a liquid (for ex.)
  2. bond enthalpy data is averaged from a range of values of bond enthalpies in a range of similar molecules
45
Q

describe how the activation energy of a reaction can be determined

A
  1. carryout the reaction at several temperatures
  2. plot 1/T against the log rate constant (k)
  3. use Ea = - gradient x R to calculate for the Ea
46
Q

explain why calcium compounds and sodium compounds give off different color flames

A

electrons are excited by the gas flame causing them to be promoted to higher energy levels and when they fall back to ground state, they release energy, and the energy difference between the levels is different for Na and Ca causing the color that is observed to be different

47
Q

the C-N bonds in urea are shorter than might be expected for a single C-N bond. explain why

A

the electrons are delocalized across the molecule

48
Q

outline how strong acids and bases are different

A
  1. strong acids fully dissociate in solution whereas weak acids only partially dissociate in solution
  2. strong acids are more conductive, lower pH and undergo faster reactions
  3. BUT the totally amount of products produced is the same
49
Q

explain why copper(II) solution is blue

A

orange light is absorbed so the complementary color is observed; copper (II) has partially filled d-subshells; ligands interact differently with the d subshells causing them to split into 2 higher energy and 3 lower energy levels; when white light strikes the complex ion, it is absorbed which promotes an electron to a higher energy level; the energy gap corresponds to the orange light which is absorbed

**NOTE THAT solution suggests the ligand for the complex ion is WATER

50
Q

describe the bonding in metals

A

electrostatic attractions between positively charged nuclei and a sea of delocalized electrons

51
Q

what does a more reactive metal mean (in terms of redox)

A

it is more readily oxidized

52
Q

comment on how international cooperation has contributed to the lowering of CFC emissions responsible for ozone depletion

A

led to governments passing legislation (montreal protocol), technologies developed and data could be shared

53
Q

suggest why propanal is a minor product obtained from the conversion of propene to propanone

A

propan-1-ol is formed as a minor product of the addition of water due to a primary carbocation formed. the primary alcohol is then oxidized into an aldehyde

54
Q

identify the major species present at the buffer region on a ph curve

A

CH3COOH and CH3COO- (i.e. the weak acid and the salt)

55
Q

identify the major species present at the equivalence point on a ph curve

A

CH3COO- (the salt) and water

56
Q

identify the major species present after the equivalence point on a ph curve

A

the salt and OH- ions

57
Q

how would you describe something that does not have a trend

A

no clear trend observed

58
Q

explain how the double helical structure of DNA is stabilized once formed

A

phosphate group on backbone has H bonding and ion dipole interactions between phosphate groups and histones, H bonding occurs between bases and the, hydrophobic interactions between predominately non-polar interior

59
Q
A

Chemistry (12 decks)

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