Random Markscheme Shit

Question 1

Compare and contrast acid and alkaline ester hydrolysis

Answer 1

-both lead to the formation of an alcohol
-acid hydrolysis is reversible, alkali hydrolysis is irreversible
-acid hydrolysis produces the carboxylic acid and alkali produces the carboxylate ion (that needs to be protonated to form the acid)
-acid acts as a catalyst and alkali acts as a reactant

Question 2

Why does phenol requires milder reaction conditions than benzene for electrophilic substitution

Answer 2

-the lone pair on the oxygen atom is donated into the pi cloud of delocalised electrons as it overlaps with it
-this increases the electron density of the benzene ring making it more susceptible to electrophilic attack

Question 3

How do u determine a suitable indicator from a titration curve

Answer 3

-the indicator needs to change colour in the vertical section of the curve
-choose and indicator with a pH range that lies within the vertical region of the titration curve

Question 4

Explain how the region on a titration curve before the vertical region acts as a buffer

Answer 4

-contains a large reservoir of acid and its conjugate base (name the ions present)
-the base (name it) will react with added acid (write the equation)
-the acid (name it) will react with added base (write equation)

Question 5

PH of the salt formed from a weak acid and strong base

Answer 5

Around 9

Question 6

PH of salt formed from a weak acid and weak base

Answer 6

Around 7

Question 7

PH of salt formed from strong acid and strong base

Answer 7

Around 7

Question 8

PH of salt formed from a strong acid and weak base

Answer 8

Around 5

Question 9

How can you use data of the concentration of a reactant at given times to determine that a reaction is neither zero nor first order

Answer 9

-not zero order if the rate is not constant
-not first order if the half life is not constant (time taken from concentration to half isn’t equal)

Question 10

Describe how to draw distillation apparatus

Answer 10

-heat source, round bottomed flask with reaction mixture, anti-bumping granules sealed at the top with a thermometer going in thats within the still head (make super clear that the thermometer is stuck within some sealed glass tubing)
-diagonally downwards condenser with water jacket drawn around it and water going in at the bottom and out of the top
-collection vessel that isn’t sealed with a little tap for pressure release before the liquid hits the flask (goes around the bend)

Question 11

Explain why during recrystallisation you leave the filtrate to cool and then carry out filtration under a reduced pressure

Answer 11

-leave to cool because the product is less soluable in cooler solvent than hot solvent so will crystallise out and soluable impurities will remain dissolved in solution
-filter under reduced pressure to remove more soluable impurities faster

Question 12

Deduce why only some of the precipitate dissolves when dilute ammonia is added to a solution of KCl and Br2

Answer 12

-the precipitate is a mixture of silver chloride and bromide
-so only the silver chloride dissolves in dilute ammonia and silver bromide does not dissolve in dilute ammonia (only in concentrated)

Question 13

Explain why the standard enthalpy change of neutralisation of ethanoic acid is less exothermic than that of hydrochloric acid

Answer 13

-ethanoic acid is a weak acid
-so some energy is used to fully ionise the ethanoic acid

Question 14

Give the name and appearance of the gas other than oxygen given off when a group 2 nitrate is heated

Answer 14

-nitrogen dioxide
-brown gas

Question 15

Write the equation for the decomposition of sodium nitrate

Answer 15

2NaNO3 —> 2NaNO2 + O2

Question 16

Describe the apparatus used to compare the decomposition of metal carbonates and how the rate of decomposition would be calculated

Answer 16

-place some solid metal carbonates into a boiling tube and attach a bung and delivery tube into another boiling tube containing limewater then heat the metal carbonates using a Bunsen burner
-compare the time taken for the limewater to go cloudy

Question 17

Explain why magnesium carbonate decomposes more readily on heating that barium carbonate

Answer 17

-the magnesium ion is smaller than the barium ion
-which polarises and distorts the electron cloud of the carbonate ion more
-and so weakens the C-O bond more so it requires less energy to break

Question 18

Explain using two equations how iron (II) catalyses the reaction between iodide ions and peroxidisulfate ions

Answer 18

2Fe2+ + S2O82- —> 2Fe3+ + 2SO42-
2Fe3+ + 2I- —> 2Fe2+ + I2

Catalysis is possible because of the variable oxidation state of iron, so both steps now involve oppositely charged ions (lower activation energy)

Question 19

Why is tungsten not a suitable replacement for platinum in a catalytic converter given that the strength of gaseous adsorption to tungsten is much stronger than that of platinum

Answer 19

The adsorption of gases is too strong and so desorption would be too slow

Question 20

Water might be expected to have a lower boiling point that hydrogen sulfide but it doesn’t. Why?

Answer 20

-expected lower boiling point because water has fewer electrons than hydrogen sulfide so water has weaker London forces however the boiling point is actually higher since water has hydrogen bonds between molecules which are stronger than London forces so require more energy to break

Question 21

Explain why both water and carbon dioxide molecules have polar bonds but only water is polar

Answer 21

-oxygen is more electronegative than hydrogen and carbon which results in a polar bond in which oxygen has a partial negative charge and carbon and hydrogen have a partial positive charge
-carbon dioxide is symmetrical and so the dipoles cancel out
-water is not symmetrical due to the presence of two lone pairs on the central oxygen atom which give the molecule a bent shape so the dipoles do not cancel

Question 22

Describe the dot and cross diagrams of H3O+ and OH-

Answer 22

H3O+ is two H atoms form normal covalent bonds to the O and one H atom forms a dative covalent bond (uses 2 O electrons) and the O atom has a lone pair

OH- is one H atom forming a normal covalent bond, 2 lone pairs on the O atom and one other lone pair on the O atom consisting of one O electron and one H electron

Question 23

Predict the sign of the enthalpy change of ionisation of water

Answer 23

Positive sign because Kw increases as temperature increases (so more ions formed at a higher temperature so must be an endothermic process)

Question 24

Compare and contrast the origin of the colour of a copper complex with the colour of a copper ion in a flame test

Answer 24

-for both, the difference in energy levels determines the colour of the flame test or complex ion
-for a flame test, heat energy results in electron promotion and the return of an electron to its lower energy state, in which it releases light energy, produces a colour
-for a complex ion, d orbitals are split due to presence of ligands and light energy is needed for electron promotion so the wavelength of light not absorbed is reflected and seen as visible colour

Question 25

What is the main statement true of a buffer solution (Its intended purpose)

Answer 25

Resists changes in pH if small quantities of acid or base are added

Question 26

Explain how the buffer system in the blood helps control blood pH when extra carbon dioxide is present due to strenuous exercise

Answer 26

-carbon dioxide dissolves in the blood to form more carbonic acid -the equilibrium will thus shift right and produce more H+ ions -the large reservoir of HCO3- ions combine with these H+ ions which helps to control blood pH

Question 27

Describe how to use a titration curve to determine the value of Ka for propanoic acid

Answer 27

-determine pH at the point when half of the acid is neutralised (this equals pKa) -Ka= 10-pH

Question 28

Deduce, by referring to Kp, how the number of sulfur dioxide molecules will change if more oxygen is added to the equilibrium: 2SO2 + O2 <—> 2SO3

Answer 28

-to ensure that Kp stays the same, as only temperature changes the value of Kp, the number of sulfur dioxide molecules decreases because equilibrium shifts right

Question 29

A flame test was carried out on a mixture of barium chloride and magnesium chloride. Hows does the presence of magnesium ions affect the appearance of the flame colour of barium ions

Answer 29

There is no change; the barium ions produce the same green colour because magnesium ions dont have a flame colour since they emit light of a wavelength beyond that of the visible light spectrum

Question 30

Describe the bonding in platinum

Answer 30

-giant metallic lattice of positive metal cations in a sea of delocalised electrons, with strong electrostatic forces of attraction between the cations and sea of delocalised electrons

Question 31

Why is the first ionisation energy of sodium greater than potassium

Answer 31

-the outer electron in a sodium atom is closer to the nucleus than that of potassium because sodium ions are smaller -this means that the valence electron of sodium experiences less shielding from inner electron shells and so requires more energy to overcome -this outweighs the effect of potassium having a greater effective nuclear charge than sodium

Question 32

Why do the successive ionisation energies of the same element increase

Answer 32

The electron being removed is closer to the nucleus so the same number of protons is attracting a decreasing number of electrons

Question 33

Why are bond enthalpy values always positive

Answer 33

Breaking bonds is endothermic and so requires energy

Question 34

Why is it that only the proton from the carboxylic acid group, and not from the methyl group, is donated from a carboxylic acid

Answer 34

-the similar electronegativity values of C and H means there is a lack of C-H bond polarity, whereas the O-H bond is much more polar -could also say how loss of H from OH made possible by thr delocalisation of charge of the carboxylate ion making it more stable

Question 35

Why does the pH of a buffer solution of butanoic acid hardly change when a few drops of sodium hydroxide are added

Answer 35

-the pH stays approximately constant because there is a large reservoir of undissociated acid and so the ratio of acid to salt does not change The reaction that occurs is C3H7COOH + NaOH —> C3H7COONa + H2O

Question 36

Explain why hexaaquacobalt (III) and hexaaminecobalt (III) are coloured and have different colours

Answer 36

-they are coloured because the presence of ligands causes the d orbitals to split into higher and lower energy levels -the difference in energy depends on the ligands -different energy gap means electrons absorb different wavelengths of light to be promoted to a higher energy level -the unabsorbed wavelengths are reflected

Question 37

Compare and contrast the complex ions formed with cobalt (III) ions and ethane-1,2-diamond vs EDTA4-

Answer 37

-both ligands form dative covalent bonds to the Co3+ ion -both complexes are octahedral with a coordination number of 6 -EDTA is hexadentate whereas ethane-1,2-diamine is bidentate -the complex with EDTA has a 1- charge whereas the complex with en has a 3+ charge -complex with EDTA is more stable as there is an increase in the entropy of the system

Question 38

Using the equation for Gibbs, predict when a reaction will be feasible base on its enthalpy change value and entropy

Answer 38

Gibbs= Enthaply change-(temp in K x entropy change of system) -Gibbs needs to be negative for a reaction to be feasible -if entropy is positive and enthalpy is negative a reaction is always feasible -if entropy is negative and enthalpy is positive a reaction is never feasible -if entropy is positive and enthalpy is positive, the reaction will only be feasible if the magnitude of TS is greater than the magnitude of H -if entropy is negative and enthalpy is negative the reaction will only be feasible if the magnitude of H is greater than the magnitude of TS -even if feasible a reaction may not occur if hindered by kinetic factors (Such as high activation energy)

Question 39

Explain why “Scandium and zinc are both d block elements but not transition metals”

Answer 39

-both elements are d block elements as they have their last added electron in the d sub shell -but neither are transition metals as neither form at least one stable ion with partially filled d orbitals -Zn2+ has completely filled d orbitals -Sc+ has completely empty d orbitals (Use their electronic configurations to prove)

Question 40

Explain why the chromium complex ion is coloured

Answer 40

-ligands cause the d orbitals to split into higher and lower energy levels -light energy is absorbed by electrons which promotes them to higher energy d orbitals -the remaining light that is of a complementary wavelength to that of the light absorbed is reflected as colour

Question 41

When a ligand exchange reaction occurs with hexaaquachromium and EDTA the equilibrium constant is very large. By referring to entropy changes explain why

Answer 41

-equilibrium lies very heavily to the right -because there is an increase in the entropy of the system -as 2 moles of reactants form 7 moles of products

Question 42

Explain why 2-methylpentane is soluable in hexane but not water

Answer 42

-Insoluble in water as it cannot hydrogen bond to water -soluble in hexane as London forces in both compounds are of a similar strength, meaning the forces in the mixture are of a similar magnitude to the forces in each separate liquid

Question 43

Explain why KBr is soluable in water but not hexane

Answer 43

-soluble in water as the ions get hydrated when dissolved -the enthaply of hydration of KBr is greater than the energy needed to break apart the lattice -KBr is in soluable in hexane as any London forces that form between KBr and hexane will be of a smaller magnitude than the forces between K+ and Br- ions

Question 44

Explain why 2 times the value of C-C bond enthalpy cannot be used to find the value of C=C bond enthaply

Answer 44

-C=C bond is weaker than 2C-C bonds as it consists of a pi and a sigma bond rather than 2 sigma bonds

Question 45

Explain why a reaction may always be feasible in the gaseous state

Answer 45

-total entropy change is always positive because entropy of system and of surroundings are always positive Could also say -Gibbs always negative -as enthaply change is negative and entropy of system is positive

Question 46

Give the colour change at the end point of the titration in which C2O4- ions are in the conical flask and MnO4- ions are in the burette

Answer 46

From colourless to pale pink (the C2O4- is naturally colourless so when the MnO4- is in excess it appears pink)

Question 47

Why is sulphuric acid added to the reaction between C2O4- and MnO4- ions (an auto catalytic reaction)

Answer 47

To provide the hydrogen ions needed as a reactant in the balanced equation

Question 48

Describe how to draw conventional cell diagram

Answer 48

-If mixture of ions then Pt(s) on very outside of either half cell, if metal then solid metal -two dotted lines in middle for salt bridge -oxidation half cell on left, reduction half cell on right -separate reactants and products of each half cell with a comma and don’t include electrons

Question 49

Magnesium powder is added to a beaker of water with a few drops of universal indicator, and a test tube filled with water is left upside down in it. What visual observations will be made after a few days?

Answer 49

-universal indicator changes colour from green to blue -gas collects at the top of the test tube (H2) causing the water level in the test tube to drop

Question 50

What do all the halogens look like at room temp and as gas

Answer 50

CL=pale green gas Br=brown liquid and brown gas I=a grey solid and a purple gas

Question 51

Give a possible reason why a disporprotionation reaction with a negative Ecell value may occur a little bit at 298K anyway

Answer 51

-the concentration may not be 1mol per dm^3 (non standard) -excess water used -disproportionation is an equilibrium system

Question 52

What factors determine the strength of an ionic bond

Answer 52

A stronger ionic bond will be between: -smaller ions (irrespective of charge) -higher charge ions

Question 53

Why does ice have a lower density than water at 0 degrees

Answer 53

-at 0c ice is arranged in a lattice of hexagonal rings -at 0c water molecules have less distance between them and so water is more dense than ice are there are more molecules in the same volume

Question 54

Write the ionic equation for the reaction between magnesium oxide and an acid

Answer 54

MgO + 2H+ —> Mg2+ + H2O

Question 55

In terms of ionisation energies, why can transition metals show variable oxidation states

Answer 55

The successive ionisation energies are close in value so there’s only a gradual increase in them