paper 1+2 Flashcards
Suggest how to detect if an alcohol and carboxylic acid have reacted.
If an ester has formed, there will be a sweet smelling liquid.
Suggest why an ester mixture would be poured into a sodium hydrogencarbonate solution.
To react with and neutralise excess acid.
Suggest why the reaction: CH3CHO + H20 –> CH3CH(OH)2 is slower than the reaction of water with chloroethanal.
. C in C=O is less electron deficient
. CH3 has positive inductive effect.
. Therefore higher Ea.
Define relative atomic mass
Average mass of 1 atom of an element compared to C12 where an atom of C12 has mass of 12.
Define relative atomic mass
Average mass of 1 atom of an element compared to C12 where an atom of C12 has mass of 12.
State what must be done to maintain EMF of fuel cell when in use.
Keep concentration of reactants constant.
What makes something a major product?
- Major product formed by more stable carbocation
- Due to more methyl groups providing positive inductive effect
Identify a catalyst used in a catalytic converter
Palladium or Rhodium or Platinum
Conditions for thermal cracking
- High pressure (7000kPa)
- High temperature (400-900 C)
- Produces mostly alkenes
Conditions for catalytic cracking
- Moderate pressure
- High temperature (450 C)
- Zeolite catalyst
- Produces branched and cyclic alkanes + aromatic hydrocarbons
Define fraction in fractional distillation
Compounds with a similar boiling point.
Explain how different fractions are obtained by fractional distillation
- Crude oil is heated to vaporise it
- Vapour passes into fractionating column
- Fractions separated by boiling point
- Due to top of tower being cooler than the bottom.
Name the fractions
. Gasoline . Naptha . Kerosene . Gas oil . Mineral (lubricating) oil
Giraffes Never Kiss Girls Moneyless
Bonding in: NH4+, H3O+, NH3BF3 ?
dative covalent.
Suggest why iodide ions are stronger reducing agents than chloride ions
- Iodide ions are larger
- They have more shielding
- Electron lost from iodine shell is less strongly attracted to nucleus.
Write equation for chlorine with cold, dilute, aqueous NaOH
Cl2 + 2NaOH –> NaClO + NaCl + H2O
Reaction of chlorine with water
Cl2 + H2O –> HClO + HCl
Reaction of chlorine in water in sunlight
2Cl2 + 2H2O –> 4H+ + 4Cl- + O2
NaF + H2SO4
NaF + H2SO4 –> NaHSO4 + HF
NaCl + H2SO4
NaCl + H2SO4 –> NaHSO4 + HCl
NaBr + H2SO4
Acid-base step, redox step, overall equation
Acid-base step: NaBr + H2SO4 –> NaHSO4 + HBr
Redox step: 2HBr + H2SO4 –> Br2 + SO2 + 2H2O
Overall equation: 2NaBr + 3H2SO4 –> 2NaHSO4 + SO2 + Br2 + 2H2O
NaI + H2SO4
Acid-base: NaI + H2SO4 –> HI
2HI + H2SO4 –> I2 + SO2 + 2H2O
6HI +H2SO4 –> 3I2 + S + 4H2O
8HI + H2SO4 –> 4I2 –> H2S + 4H2O
State the type of structure shown in a crystal of silicon and explain why the melting point is very high.
- Macromolecular
- Many strong covalent bonds
- Bonds must be broken
Explain what makes aluminium malleable
Layers of atoms can slide over each other
How do hydrogen bonds form in proteins
. N and O are very electronegative
. So C=O and N-H are polar
. Hydrogen bonds form between O and H
. Lone pair of electrons on oxygen and nitrogen are strongly attracted to Hd+
What is the function of a salt bridge
- The ions in the ionic substance in the salt bridge move through the salt bridge
- To maintain charge balance / complete the circuit
State the major advantage of using fuel cells
An internal combustion engine wastes more energy
Hydrogen fuel cell reaction at positive and negative electrode:
Positive: O2 + 2H2O + 4e- –> 4OH-
Negative: H2 + 2OH- –> 2H2O + 2e-
How is electric current produced in hydrogen-oxygen fuel cell
Hydrogen electrode produces electrons
Oxygen electrode accepts electrons
Explain how a solution containing sodium hydrogencarbonate and sodium carbonate can act as a buffer when small amounts of acid or small amounts of alkali are added.
. Acid: Increase in concentration of H+ ions, equilibrium moves to the left.
Allow H+ ions react with carbonate ions (to form HCO3)
. Alkali: OH- reacts with H+ ions, equilibrium moves to the right (to replace the H+ ions)
. Concentration of H+ remains (almost) constant
Suggest a suitable piece of apparatus that could be used to measure out the sodium hydroxide solution.
Explain why this apparatus is more suitable than a pipette for this purpose
Burette - it can deliver variable solutions.
Define weak acid
Only slightly dissociated
Suggest what substance might be present in the air to cause the pH of a solution to change.
CO2 - decreases pH of solution
CO2 + 2OH− –> CO32− + H2O
or
CO2 + OH- –> HCO3-
Explain why chloroethanoic acid is a stronger acid than ethanoic acid
Chlorine is electronegative so it withdraws electrons and weakens O-H bond.
Suggest how a student doing this experiment could check that all the water had been removed
Re-heat to check mass is unchanged
State the reagents and conditions necessary to make an alkene from an alcohol
H2SO4
Heat
Describe a test to show that ammonia has evolved
. Concentrated HCl
. White fumes.
Explain briefly why a pH meter should be calibrated before use.
over time / after storage meter does not give accurate readings
Why is it important for containers in calorimeters to have the same dimensions
Absorption is proportional to path length/ distance travelled through the solution.
Why is a coloured filter used in colorimetry
To select wavelength/ colour that is most strongly absorbed by sample.
Explain why different amino acids have different Rf values
. Amino acids have different polarities
. Therefore, have different retention on the stationary phase or different solubility in the developing solvent
How to make an alkene from a haloalkane
KOH with heat/ ethanolic conditions
The minor product in this reaction mixture is 2-bromo-3-methylbutane. Why is it a minor product as opposed to 2-bromo-2-methyl butane?
Reaction goes via intermediate carbocation.
Tertiary carbocation is more stable.
In practice, KCN rather than HCN is added to the carbonyl compound.
Given that Ka for HCN = 4.0 × 10–10 mol dm–3, suggest why the reaction with HCN is very slow.
Weak acid.
[CN-] very low.
Outline briefly why chromatography is able to separate a mixture of compounds
. Solvent is moving
. There is a stationary phase
. Amino acids have different Rf values.
Suggest why the enthalpy change for the reaction in part (c) is approximately zero.
. Same number and type. of bonds broken as bonds made
.Bonds formed have the same enthalpy as bonds broken.
In terms of electrostatic forces, suggest why the electron affinity of fluorine has a negative value.
There is an attraction between the nucleus / protons and (the added) electron(s)
Energy is released (when the electron is gained)
Suggest why hydration of the chloride ion is an exothermic process.
Water has H+
Chloride ion is attracted to H ion in water.
Define lattice enthalpy of dissociation
Enthalpy needed to separate 1 mol of ionic substance into its constituent ions in gaseous form.
Explain why the first electron affinity of oxygen is exothermic.
There is an attractive force between the nucleus of an O atom and an external electron.
Pure ice can look pale blue when illuminated by white light. Suggest an explanation for this observation
. Complementary colour to blue is absorbed
. Blue light is transmitted.
Write two equations to show how Mn2+ acts as an autocatalyst in
2MnO4– + 16H+ + 5C2O42– –> 2Mn2+ + 8H2O + 10CO2
MnO4- + 8H+ + 4Mn2+ –> 5Mn3+ + 4H2O
2Mn3+ + C2O42- –> 2Mn2+ + 2CO2
Define complex ion
Has ligands joined by coordinate bonds
Why can electron repulsion theory not predict the shape of a complex ion
There are too many electrons in d sub-shell orbital.
Define bidentate
Bidentate ligand donates to electron pairs from two atoms to a transition metal ion.
Explain why [Al(H2O)6]3+ has a pH < 7
[Al(H2O)6] 3+ ⇌ [Al(H2O)5(OH)] 2+ + H+
Al3+ has high charge density + small size
In reaction with water, it weakens OH bond and releases H+/
rate = k[E]
Explain qualitatively why doubling the temperature has a much greater effect on the rate of the reaction than doubling the concentration of E.
Reaction only happens when molecules have E>Ea
Doubling temperature causes many more molecules to have this Ea, whereas doubling the concentration only doubles the number of molecules with Ea.
Silver complexes can be used to identify a particular organic functional group.
Give one example of a silver complex that can be used in this way and state the organic functional group it identifies
[Ag(NH3)2]+
aldehyde
Explain how stereoisomerism arises in pent-1-ene and state which isomer is less polar
. Trans pent-1-ene
. Lack of rotation around C=C bond and each carbon in double bond has two different groups attached.
Explain the bonding and the shape of a benzene molecule
. Spare electrons overlap to form a pi cloud . Electrons are delocalised . Planar . 120 bond angle . C-C bonds are equal in length
Explain why the enthalpy of hydrogenation of cyclohexa-1,3-diene is not exactly double that of cyclohexane.
. Double bonds are alternating/ separated by a single bond
. There is some delocalisation
Explain why an aqueous solution is obtained in the reduction of nitrobenzene even though phenylamine is insoluble in water.
Phenylamine is present as an ionic salt.
Write the molecular formula of the standard used in 13C n.m.r. spectroscopy.
Give two reasons why this compound is used.
C4H12Si
. Non toxic
. Volatile
. One peak
Explain why the reaction of an aldehyde with KCN makes a racemic mixture.
. There is a planar carbonyl bond
. Nucleophilic attack is equally likely from either sides.
Explain why the total volume of the mixture would not need to be measured to allow a correct value of Kc to be calculated.
Equal moles on each side of the equation.
State in general terms what determines the distance travelled by a spot in TLC
Balance between solubility in moving phase and retention by stationary phase.
Amine C6H4CH2CH2NH2 can be made in a three step synthesis starting from methylbenzene. Suggest the structures off the two intermediate compounds + give reagents and conditions.
- C6H5CH2Cl –> Cl2 + UV
- C6CH2CN –> KCN alcoholic
- H2 / Ni
Describe a test tube reaction to distinguish between sodium oxide and phosphorus oxide
. Add water and then use litmus paper to test pH
.Sodium Oxide gives a pH of 13
. Phosphorus oxide gives a pH of 0
A shirt was made from polyester. A student splashed aqueous sodium hydroxide on a sleeve. Holes appeared. Name the type of reaction that occurred between the polyester and aqueous sodium hydroxide. Explain why the aqueous sodium hydroxide reacted with the polyester.
. Hydrolysis
. d+ C in polyester reacts with OH-
Test for acyl chloride
AgNO3
white ppt
Cold water
white musty fumes
Samples of the reaction mixture are removed at timed intervals and titrated with alkali to determine the concentration of H+(aq).
State and explain what must be done to each sample before it is titrated with alkali
Stop reaction by dilution
State and explain why different volumes of water are added to mixtures B, C, D and E in an experiment to measure rate of reaction of propanone.
To make volumes constant for all mixtures.
So that volume of propanone is proportional to concentration.
Each sample taken from the reaction mixtures is immediately added to an excess of sodium hydrogencarbonate solution before being titrated with sodium thiosulfate solution.
Suggest the purpose of this addition.
Explain your answer.
To stop / quench the reaction at that time.
By removing the acid catalyst for the reaction (by neutralisation)
Suggest why initial rates of reaction are used to determine these orders rather than rates of reaction at other times during the experiments.
At time = 0, concentrations are known.
What are some physical properties of SiO2
. Brittle
. Non-conductive
. Insoluble
State the type of bonding in these basic oxides.
Explain why this type of bonding causes these oxides to have basic properties.
Ionic
Have O2- ions which accept protons to make OH-
Suggest one reason why electron pair repulsion theory cannot be used to predict the shape of the [CoCl4]2− ion.
Too many electrons in d shell orbital
Why is graphite soft?
Planes (1)
weak (bonds) forces between planes (1)
Define periodicity
Repeating patterns of chemical reactions
Suggest a reagent for [Fe(H2O)6]3+ –> [Fe(H2O)6)]2+
Excess Zn in acid (HCl)
A buffer solution has a constant pH even when diluted. Use a mathematical expression to explain this.
[HX]/[X-] stays almost constant
How to calculate EMF of cell
RHS - LHS
Student dilutes 25cm3 of 0.5moldm-3 propanoic acid by adding water until total volume is 100cm3. Ka = 1.35 x10-5
Calculate pH of diluted solution
[C2H5COOH] = 0.125 pH = 2.89
Perfume is a mixture of fragrant compounds dissolved in a volatile solvent.
When applied to the skin the solvent evaporates, causing the skin to cool for a short time. After a while, the fragrance may be detected some distance away. Explain these observations.
. Solvent has low bp or weak intermolecular forces or evaporates quickly (1)
. (Solvent) needs energy to evaporate (to overcome intermolecular forces)
or valid reference to latent heat of vaporisation (or evaporation is
endothermic) (1)
OR higher energy or faster molecules more likely to escape
so mean energy (and hence temperature) falls
. Energy taken from the skin (and so it cools) (1)
. Fragrance or perfume (molecules) slowly spreads (through the room) (1)
. By random movement or diffusion (of the perfume / fragrance) (1)
Compare structure and bonding in graphite and diamond
Both macromolecular
Diamond is strong due to 3D structure
Graphite is soft as layers can slide over each other, as there are weak VdW forces between layers
Diamond is not a conductor, graphite is
Both have many strong covalent bonds that require high energy to overcome
How does hydrogen bonding in HF occur
There is a large difference in electronegativities
There is a dipole produced
Hd+ is attracted to Fd-
Explain why third ionisation energy in magnesium is higher than second ionisation.
. 3rd ionisation removes electron from 2p instead of 3s, which is closer to the nucleus so is more attracted to the nucleus as it has less shielding
. so more energy is needed to remove it.
The enthalpy of cyclohexa-1,3-diene is not exactly double that of cyclohexene. Explain why.
Double bonds are separated by a single bond, there will be some delocalisation.
What reagent is needed to make 1-phenylpropan-1-ol from phenyl-c=o-ch2ch3
NaBH4
nucleophilic addition
Primary amines can be prepared by the reaction of halogenalkanes with ammonia by reduction of nitriles. Explain why it’s better to prepare primary amines from nitriles rather than halogenalkanes.
Nitriles have a no further reaction
Halogenalkanes have further reactions with primary amines.
Give two ways of maximising yield of aldehyde when boiling
. Cool distillate
. Keep below boiling point
How do cis/trans isomers arise?
There is lack of rotation around C=C bonds, 2 different groups attached to each carbon
Explain why Si(CH3)4, CCl4 and CDCl3 are used for H NMR spectroscopy
. CDCl3 or CCl4 solvent
. TMS as reference / calibration / standard / peak
at 0 (ppm)
. Inert (so unlikely to react with the sample allow if
inert tied to either TMS or CDCl3 or CCl4)
CCl4 or CDCl3 as solvent:
. (Both) have no H (atoms so give no signals in spectrum) tied to either CDCl3 or CCl4
. CCl4 non polar (- good solvent for non-polar organic molecules)
. CDCl3 polar covalent molecule (– good solvent for polar organic compounds)
TMS:
3a (Lots (12) of equivalent H to) give one signal / single environment
3b Signal in an area away from other typical H signals / peak upfield from others
3c Easy to remove / volatile / low bp
Give a reagent for the hydrolysis of a proteinn
Concentrated Hcl
During the experiment the concentration of cisplatin is measured at one-minute intervals.
Explain how graphical methods can be used to process the measured results, to confirm that the reaction is first order.
. Plot concentration (y-axis) against time (x-axis) and take tangents / (calculate the) gradients (to calculate rates)
. Plot rate/gradients against conc
. Straight line through origin / directly proportional confirms first order
Suggest why lysine leaves the column after alanine in chromatography
Lysine ion has a greater attraction to the stationary phase
As it has a more positive charge
Half equation to reduce acidified potassium dicrhomate
Cr2O72– + 14H+ + 6e– → 2Cr3+ + 7H2O
Half equation for reduction of Tollen’s reagent
[Ag(NH3)2]+ + e– → Ag + 2NH3
Explain how three isomeric products are formed when HY reacts as but-1-ene
Major product is a pair of enantiomers
Other product is 1-bromobutane (minor product)
Which is formed via the primary carbocation
How to form ethanol by fermentation
glucose --> 2xethanol + 2xCO2 . yeast, no air, temperature of 30-40 \+ sugar is renewable resource \+ cheap equipment - slow, high production cost - ethanol made is not pure
how to make ethanol from ethene
hydration
. high temperature, high pressure, concentrated H3PO4
+ faster, pure product, continous process
- High tech equipment
- ethene is not renweable
Suggest why chemists use methods with fewer steps
Less energy used + better yield
Suggest why chemists use methods with high percentage atom economy
Less waste
Why is ozone beneficial for organisms
Absorbs harmful UV
State how CFCs form chlorine atoms in upper atmosphere
C-Cl bonds broken by homolytic fission
What catalyst is used in Haber process
iron
What catalyst. is used in production of methanol from CO
chromium and zinc oxides
What is the function of the platinum electrode
Allows transfer of electrons
(straight line going down) - explain how the graph shows that the order is zero in respect to H+
The gradient is constant as H+ changes
How to measure melting point
. Put sample in melting point apparatus
. Heat slowly
. Lower/range of melting points suggests and impurity
