CHEM PPQ Flashcards by Sajan Jasotharan

This question is about magnesium, bromine and magnesium bromide.
Table 16.1 shows some physical properties of magnesium, bromine and magnesium bromide.

Substance Melting point / °C Electrical conductivity
Solid Liquid:
.Magnesium 711 Good Good
.Bromine −7 Poor Poor
.Magnesium bromide 650 Poor Good

Explain the physical properties shown in Table 16.1 using your knowledge of structure and
bonding

magnesium
.has a giant lattice structure and metallic bonding so has a high mp
.conducts as delocalised electrons can move

bromine:
.simple molecular
.london forces between molecules so low mp
.cant conduct as there is no mobile charge carriers

magnesium bromide:
.giant lattice structure + ionic bonding between opposietly charged ions= high mp
.in solution ions can move so can conduct electricity
.

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This question is about some elements in Period 4 of the periodic table.
The table shows the melting point and electrical conductivity of two elements in Period 4.

Element Melting Point / °C Electrical conductivit:
Calcium 842 Good
Bromine –7 Poor
Use your knowledge of structure and bonding to explain the properties in the table.

Calcium:
.giant metallic lattice
.has metallic bonding = high mp
.has delocalised electrons that can move

bromine:
.simple molecular
.has london forces = low mp
.no free charge carriers

.metallic bonds are stronger than london forces

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The reaction of barium with bromine is more vigorous than the reaction of calcium with
bromine.
Explain why [3]

.Ba has a greater atomic radius = nuclear attraction is less in Ba = easier to remove outer electrons in Ba

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SiO2 and CO2 are oxides of Group 14 (Group 4) elements.
Solid SiO2 melts at 2156 °C. Solid CO2 melts at −56 °C.
Suggest the type of lattice structure in solid SiO2 and in solid CO2 and explain the difference in
melting points in terms of the types of force within each lattice structure.

.SiO2 has a gaint covalent lattice whereas CO2 has a simple molecular structure

.SiO2 has covalent bonds and CO2 has london forces
.covalent bonds are stronger than london forces

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The reactivity of the Group 2 elements Mg–Ba increases down the group.

.atomic radius increases
.so nuclear attraction decreases
.less energy is needed to remove electron

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B and C are ionic compounds of two different Group 1 elements.
The molar masses of B and C are both approximately 140 g mol−1.
A student dissolves B and C in water in separate test tubes and analyses the solutions.
The observations are shown below.

Test
Addition of HNO3(aq)
followed by BaCl2(aq)

B(aq:
bubbles
no change

C(aq)
no change
white precipitate

Use this information and the observations to identify the formulae of B and C.
Explain your reasoning.

.bubbling when HNO3 is added shows that B is a carbonate
.a white percipitate when BaCl2 is added shows that C is a sulfate

B = K2CO3
C = Na2SO4

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First ionisation energies decrease down groups in the Periodic Table.
Explain this trend and the effect on the reactivity of groups containing metals.

.larger atomic radius
.nuclear charge increase outweighted by increased radius
.less electrostatic attraction to outer electrons = reactivity increases down groups

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What is the name given to this repeating pattern of properties?

periodicity

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The melting points of the Period 3 metals sodium and magnesium are shown below.

Metal Melting point / °C
sodium 98
magnesium 649

Explain the differences in the melting points of sodium and magnesium, using the model of
metallic bonding.

.magnesium has more outer electrons
.Mg ions have greater charge density
.Mg has greater attraction between ions and delocalised electrons

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State how and explain why the attraction between nuclei and outermost electrons in gaseous
atoms varies across Period 3.

.attraction increases as num of protons increases
.as outer electrons are in the same shell

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The Periodic Table is arranged in periods and groups.
Elements in the Periodic Table show a periodic trend in atomic radius.
State and explain the trend in atomic radius from Li to F.

.atomic radius decreases as nuclear charge increases
.and the electrons are in the same outer shell so there is a greater nuclear attraction on electrons

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This question is about reactions and uses of the weak acids methanoic acid, HCOOH, and
ethanoic acid, CH3COOH.
A student adds magnesium metal to an aqueous solution of ethanoic acid, CH3COOH.
A redox reaction takes place.
Write the overall equation for this reaction and explain, in terms of oxidation numbers, which
element has been oxidised and which element has been reduced.

2CH3COOH + Mg —> (CH3COO)2Mg+ H2

Mg is oxidised from 0 to 2+
H is reduced from +1 to 0

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The reaction of barium with bromine is more vigorous than the reaction of calcium with
bromine

.Ba has a larger atomic radius than Ca
.so nuclear attraction is less in Ba
.so ionisation energy for Ba is less

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Outline 2 reaction routes for preparing a solution of Ba(OH)2 from barium in the laboratory.
Include relevant equations.

.add H2O to Ba
Ba+ H2O –> Ba(OH)2+ H2

.add O2 to Ba
2Ba + O2 –> 2BaO
.then add water
BaO + H2O –> Ba(OH)2

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Write the equation for the reaction of strontium with water.

Describe two observations which would be different if the student had used calcium in
place of strontium.

Sr + 2H2O –> Sr(OH)2+ H2

.less vigourous bubbling
.dissolves slower

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. Calcium nitride reacts with water to form a solution containing two alkaline compounds.
Write an equation for this reaction.

Ca3N2 + 6H2O –> 3Ca(OH)2+ 2NH3

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This question is about Group 2 and Group 17 (7).
Barium chloride can be prepared from barium hydroxide in a neutralisation reaction.
Write the equation for this reaction. State symbols are not required.

Ba(OH)2 + HCl –> BaCl2 + H2O

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The reactivity of the Group 2 elements Mg–Ba increases down the group.

.atomic radius increases
.nuclear attraction decreases
.ionisation energy decreases

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Explain why the first ionisation energy of strontium is less than the first ionisation energy
of calcium.

.increased atomic radius
.increased electrons sheilding
.less electrostatic attraction

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A chemist carries out reactions of barium and barium nitride, Ba3N2.
Reaction 1 Barium is reacted with water.
Reaction 2 Barium nitride is reacted with water, forming an alkaline solution and an alkaline
gas.
Reaction 3 Barium is reacted with an excess of oxygen at 500°C, forming barium peroxide,
BaO2.
i. Write equations for Reaction 1 and Reaction 2.

Ba + 2H2O -> Ba(OH)2+ H2

Ba3N2 + 6H2O -> 3Ba(OH)2 + 2NH3

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A student adds a solution of bromine in an organic solvent to two test tubes.
The student adds aqueous sodium chloride to one test tube, and aqueous sodium iodide to the
other test tube.
The student shakes the mixtures, allows them to settle, and records the colour of the organic
layer in each mixture.

Sodium halide Colour of organic layer
Sodium chloride orange
Sodium iodide violet
Explain how the student’s results provide evidence for the trend in reactivity of the halogens down
group 17(7) and write an ionic equation for any reaction that takes place.
Use your chemical knowledge to explain the trend in reactivity

.orange contains bromine = no reaction
.violet contains iodine
Br2 + 2I- –> 2Br- + I2

.reactivity decreases down the group and gains electrons less easily
.due to greater atomic radius and more shielding so less nuclear attraction

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. Chlorine is used in water treatment.
State one benefit and one risk of using chlorine in water treatment

.kills bacteria but is toxic

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Explain the trend in boiling points of the halogens

.num of electrons increases
.more london forces
.more energy required to break intermolecular forces

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Bromine is used to extract iodine from a solution containing iodide ions.
i. Write an ionic equation for the reaction.

Br2 + 2I- –> 2Br- + I2

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Bromine disproportionates when it reacts with potassium hydroxide solution. Suggest an equation for this reaction.

Br + K(OH)2 -> KBr + KBrO + H2O

Precipitation reactions can be used to distinguish between halide ions. i. State the reagent needed for these precipitation reactions.

silver nitrate AgNO3

How would the appearance of the precipitates allow you to distinguish between chloride, bromide and iodide ions?

.chloride is white .bromide is cream .iodide is yellow

This question is about properties of the halogens and halide ions. Bromine can be extracted by bubbling chlorine gas through concentrated solutions containing bromide ions. Write an ionic equation for this reaction and state why this reaction takes place in terms of reactivity of the halogens.

2Br- + Cl2 --> 2Cl- + Br2 chlorine is a stronger oxidisng agent

A student carries out test-tube experiments to prove the trend in reactivity of halogens. The student is provided with the following solutions: * bromine water * aqueous iodine * aqueous barium chloride * aqueous magnesium bromide * aqueous calcium iodide. Chlorine gas and chlorine water are not available. The student carries out the minimum number of test-tube experiments using these solutions in the presence of cyclohexane (an organic solvent). * State the solutions that need to be added together in order to prove the trend in reactivity of the halogens, using the minimum number of test-tube experiments. * Describe the colour seen in the organic solvent at the end of each test-tube experiment. * Write an ionic equation for one reaction that takes place.

.BaCl2 + Br2 = yellow .Cal2 + Br2 = lilac .Br2 + 2I- --> I2 + 2Br-

. Chlorine reacts with aqueous sodium hydroxide to form bleach. Write the equation and state the conditions for this reaction.

2NaOH + Cl2 --> NaCl + NaClO + H2O

This question is about nickel and its compounds. A student is provided with samples of three nickel compounds. One sample is nickel(II) bromide, another is nickel(II) sulfate and the third is nickel(II) carbonate. The student doesn’t know which sample is which. Describe the tests that the student could carry out to identify the anion (negative ion) in each sample, and write equations for any reactions.

carbonate test: .add HNO3 .fizzing = CO2 gas = carbonate .2H+ + CO3 2– → CO2 + H2O sulfate test: .add BaCl2 .white percipitate = sulfate .Ba2+ + SO4 2– → BaSO4 halogen test: .add AgNO3 .white percipitate = chlorine .cream percipitate = bromine .yellow percipitate = iodine .Ag+ + Br– → AgBr

You are supplied with a sample of ammonium bromide. Describe simple tests that would identify the cation and anion present in ammonium bromide. Include reagents, expected observations and relevant equations.

test for bromine: .add silver nitrate and cream percipitate forms .Ag+ + Br- --> AgBr test for ammonia: .heat with NaOH .turns indicator paper blue .NH4+ + OH- --> NH3 + H2O

Describe the use of aqueous barium chloride in qualitative analysis

.use to test for sulfates .white percipitate forms

State the conditions of temperature and pressure used for standard enthalpy measurements.

298K 100kPa

formula for calculating enthalpy change

q = mcΔT q = heat energy(J) m = mass of water/solution c = 4.18 ΔH = q/moles ΔH = enthalpy change(KJ)

At the end of the experiment, the student adds a few drops of aqueous sodium chloride to the reaction mixture in the polystyrene cup to test whether all the aqueous silver nitrate has reacted. Explain how the results would show whether all the aqueous silver nitrate has reacted. Include an equation with state symbols in your answer.

.white percipitate will form if there is remaining AgNO3 Ag+ + Cl- --> AgCl

5.10 tonnes of NH3 are converted into NO. Calculate the energy released, in kJ, for this conversion. Give your answer in standard form and to an appropriate number of significant figures

.find moles .find the energy released per mole .times both numbers together

The calculated value of ΔcH for hexane from this experiment is different from the data book value. Suggest two reasons for this difference

.heat is released into the surroundings .incomplete combustion

Define standard enthalpy change of combustion

enthalpy change when one mole of a substance completely combusts with oxygen 298K 100kPa

What is meant by the term average bond enthalpy

average enthalpy change when one mole of gaseous covalent bonds are broken

What is meant by the term standard enthalpy change of formation?

when one mole of a compound is formed from its elements

The graph shows that rate of reaction decreases over time. Explain why, in terms of collision theory

.concentration decreases .less frequent collisions

Explain how a catalyst increases the rate of reaction

.lowers activiation energy by providing an alternate route .a greater proportion of molecules have more energy than the activation energy

Describe and explain the effect of increasing the pressure on the rate of this reaction.

.increases rate as molecules are closer together meaning that there are more colisions

A student was asked to carry out an experiment to determine the initial rate of reaction of zinc and hydrochloric acid. The student plans to collect a total of about 72 cm3 of hydrogen at RTP and to use an excess of zinc. The student selects the following apparatus: * the apparatus shown in the diagram * 100 cm3measuring cylinder * stop clock * 2 decimal place balance Outline how the student could carry out the experiment and explain how the results could be processed graphically. Show all working in your calculations.

.measure mass of zinc using a 2dp balance .measure vol of HCl using measuring cylinder .mix zinc and acid in flask .measure gas volume at timed intervals .plot a graph of vol against time .draw tangent a t = 0 .gradient of tangent = initial rate

State an example of a catalyst used by the chemical industry and write the equation for the reaction that is catalysed.

Ni C2H4 + H2 --> C2H6

State two ways that the use of catalysts helps chemical companies to make their processes more sustainable and less harmful to the environment.

.lowers temp .greater atom economy

Outline a method that could be used to obtain the results that are plotted on the graph. Your answer should include the apparatus required and the procedure for the experiment.

.flask .balance .stop clock .time intervals every 10s

Explain how le Chatelier’s principle can be used to predict the conditions of temperature and pressure for a maximum equilibrium yield of ammonia

pressure: .high pressure as ammonia has fewer gaseous moles temp: .low temp as the foward reaction is exothermic

Calculate the numerical value for Kc for equilibrium 24.1 under these conditions. Give your answer to an appropriate number of significant figures and in standard form.

kc = [C][D]/[A][B]

Le Chatelier’ s principle can be used to predict how different conditions affect the equilibrium position. * Using le Chatelier’ s principle, show that a low temperature and a high pressure should be used to obtain a maximum equilibrium yield of SO3. * Explain why the actual conditions used in industry may be different from the conditions needed for a maximum equilibrium yield.

TEMP: forward reaction is exo PRESSURE: right side has fewer gaseous moles INDUSTRIAL: .high temp needed to increase rate .high pressure uses alot of energy

State le Chatelier's principle

equilibrium shifts to minimise any change

A closed system is required for dynamic equilibrium to be established. State one other feature of this dynamic equilibrium

.rate of the foward reaction is equal to the rate of the reverse reaction .conc dont change

alcohol(H2SO4 + heat) -->

alkene

Compounds A, B and C are saturated hydrocarbons. The structures and boiling points of A, B and C are shown below. * Use the structures to explain what is meant by the term structural isomer. * Explain the trend in boiling points shown by A, B and C in the table.

.different structual formulae but same molecular formula .C5H12 .bp decreases with branching as there are weaker London forces due to less contact and so less energy required to break the London forces

. Compounds A, B and C all react with chlorine in the presence of ultraviolet radiation to form organic compounds with the formula C5H11Cl.

radical subsitution

Iodine monobromide, I–Br, is a polar molecule. Heterolytic fission of the I–Br bond forms an electrophile. State the meaning of the term electrophile and suggest the formula of the electrophile formed from IBr.

.electron pair donor I+

Suggest the general formula for a carboxylic acid.

CnH2n+1COOH

What is meant by the term homologous series?

group of compounds with the same functional group with each successive member differeing by CH2

What does a curly arrow represent in mechanisms?

movement of an electron pair

What is meant by the term nucleophile?

electron pair donor

alkene(halogen) --> halogenoalkane(KOH(aq)/warm) --> alkene(steam and acid catalyst) =

halogenoalkane alcohol alcohol

Explain what is meant by the term stereoisomers.

.same structual formula but different arrangement in space

test for C=C functional group

.add bromine water .becomes decolourised

Under suitable conditions, butane, C4H10, reacts with chlorine by radical substitution. A mixture of organic compounds is formed, including C4H9Cl , and compounds D and E. i. Complete the table below to show the mechanism for the initiation and propagation stages of the reaction of C4H10 with chlorine to form C4H9Cl . In your equations, use molecular formulae and ‘dots‘ (·) with any radicals

initiation: Cl2 --> 2Cl. UV propagation: C4H10 + Cl. --> C4H9. + HCl C4H9. + Cl2 --> C4H9Cl + Cl.

At room temperature and pressure, the first four members of the alkanes are all gases but the first four alcohols are all liquids. Explain this difference in terms of intermolecular forces

.alcohols have hydrogen bonds and London forces whereas alkanes only have london forces .hydrogen bond are stronger than london forces

alkane + halogen -->

halogenoalkane + Hhalogen e.g. HCl, HBr, HI

Describe how a σ-bond forms.

direct overlap of orbitals between the bonding atoms

alkene(H2 and nickel catalyst) -->

alkane

State one advantage and one disadvantage of using combustion as a method for the disposal of waste

.energy production .formation of greenhouse gases

After polymers have been used for packaging, the waste polymers need to be processed to save resources, for example, by recycling. Describe two other ways in which waste poly(propene) can be processed in a sustainable way

.combustion for energy production .use as and organic feedstock

State and explain the features of a hex-2-ene molecule that lead to E and Z isomers.

.c=c restricts rotaton .each carbon is bonding to two different groups

Radical substitution produces a mixture of organic products. Suggest two reasons why

.further subsitution .subsitution at different points of the chain

Describe how HCl is removed from the waste gases produced.

passed through a carbonate

alcohol(K2Cr2O7/H2SO4 reflux) ->

carboyxlic acid

alcohol(H2SO4/acid catalyst + heat) -->

alkene + H2O

1-Bromobutane is an organic liquid with a boiling point of 102 °C. A student prepares 1-bromobutane by reacting butan-1-ol with sulfuric acid and sodium bromide. The student boils the mixture for one hour. The equation is shown below. CH3CH2CH2CH2OH + H+ + Br− → CH3CH2CH2CH2Br + H2O The student obtains a reaction mixture containing an organic layer (density = 1.27 g cm−3) and an aqueous layer (density = 1.00 g cm−3). i. * Draw a labelled diagram to show how you would safely set up apparatus for the preparation. Outline a method to obtain a pure sample of 1-bromobutane from the reaction mixture

.draw a set up for reflux(round bottom flask, heat source, condenser) .use separating funnel to separate organic and aqueous layers .drying with MgSO4 .collect fraction distilling at 102C

A student plans to carry out this oxidation using the apparatus shown in the diagram. Give one reason why the apparatus is not suitable and describe a more suitable way of carrying out this oxidation.

.its flammable .heat under reflux or distillation

Explain, with reference to a suitable chemical test, how compound J could be identified. Your answer should not include spectroscopy

.add 2,4 DNP .forms yellow percipitate .take melting point of crystals .compare to known values

Explain what is meant by the term stereoisomers

.same structual formula .different arrangements in space

Outline the mechanism for the alkaline hydrolysis of (CH3)2CHCH2CH2Br. The structure of (CH3)2CHCH2CH2Br has been provided. Show curly arrows, relevant lone pairs and dipoles, and the products.

.C is delta positive and Br is delta negative .arrow from OH- to C .arrow from C-Br bond to Br .OH where the Br was .+ Br-

The student decides to prepare alcohol A using the same method as in the part above but using the chloroalkane (CH3)2CHCH2CH2Cl instead of the bromoalkane, (CH3)2CHCH2CH2Br. State and explain how the rates of hydrolysis of the chloroalkane and the bromoalkane would differ.

.Chloroalkane reaction would be slower .as the C-Cl bonds are stronger than the C-Br bonds

Construct an equation to show the formation of Cl * radicals from chlorotrifluoromethane Ozone is broken down by Cl * radicals in a two-step process. Write the equations for the two steps and the overall equation for this process

CF3Cl --> CF3. + Cl. O3 + Cl. --> ClO. + O2 ClO. + O --> Cl.+ O2 O3 + O --> 2O2

State two sources of nitrogen oxides in the stratosphere

lightning and aircrafts

Write equations to show how nitrogen monoxide catalyses the breakdown of ozone.

NO. + O3 --> NO2 + O2 NO2. + O --> NO. + O2

. Explain the following statements, using equations where appropriate. o Life on Earth benefits from the presence of an ozone layer. o The concentration of ozone is maintained in the ozone layer. o Compound G produces radicals which catalyse the breakdown of ozone.

.ozone absorbs UV O3 = O2 + O CF3Cl ---> Cl. + CF2Cl Cl. + O3 --> ClO. + O2 ClO. + O --> Cl. + O2 O3 + O --> 2O2

This question is about hex-1-ene, CH3CH2CH2CH2CH=CH2. Hex-1-ene is a liquid with a boiling point of 63 °C and a density of 0.67 g cm–3. Hex-1-ene can be prepared by refluxing hexan-1-ol (boiling point 157 °C) with an acid catalyst. Hexan-1-ol is a liquid with a boiling point of 157 °C and a density of 0.82 g cm–3. The equation is shown below. After reflux, the resulting mixture contains unreacted hexan-1-ol, hex-1-ene and water. The mixture is then purified. The expected percentage yield of hex-1-ene from hexan-1-ol is 62.5%. i. * A student plans to prepare 4.20 g of hex-1-ene by this method. Calculate the mass of hexan-1-ol that the student should use and explain how you could obtain pure hex-1-ene from the mixture obtained after reflux

.find moles of hexene .find moles of hexan-1-ol needed n(hexene) x percentage yield of hexan-1-ol .find mass needed .use separating funnel .dry with MgSO4 .Distillation

A student hydrolyses a haloalkane, E, using the following method. * 0.0100 mol of haloalkane E is refluxed with excess NaOH(aq) to form a reaction mixture containing an organic product F. * The reaction mixture is neutralised with dilute nitric acid. * Excess AgNO3(aq) is added to the reaction mixture. 1.88 g of a precipitate G forms Organic product, F, has a molar mass of 74.0 g mol−1 and has a chiral carbon atom. Analyse the information to identify E, F and G

G = AgBr .as Mr of percipitate = 188(1.88g/0.01 mol) .188 - 107.9(mr of Ag) = 80.1 = mr of Br- F = butan-2-ol E = 2-bromobutane

A student investigates the reaction between ethanoic acid, CH3COOH(l) and methanol, CH3OH(l), in the presence of an acid catalyst. The equation is shown below. CH3COOH(l) + CH3OH(l) ⇌ CH3COOCH3(l) + H2O(l) The student carries out an experiment to determine the order of reaction with respect to CH3COOH. The student uses a large excess of CH3OH. The temperature is kept constant throughout the experiment. The student takes a sample from the mixture every 20 minutes, and then determines the concentration of the ethanoic acid in each sample. From the experimental results, the student plots the graph below. i. Explain why the student uses a large excess of methanol in this experiment.

.it is zero order relative to the reaction

Three students carry out a rates investigation on the reaction between bromine and propanone in the presence of hydrochloric acid. CH3COCH3(aq) + Br2(aq) → CH3COCH2Br(aq) + HBr(aq) Each student investigates the effect of changing the concentration of one of the reactants whilst keeping the other concentrations constant. Their results are shown below. Results of student 3 Experiment [Br2(aq)] / mol dm−3 [CH3COCH3(aq)] /mol dm−3 [H+(aq)] / mol dm−3 Initial rate / 10−5 mol dm−3 s−1 1 0.004 1.60 0.20 1.25 2 0.004 1.60 0.40 2.50 Explain how the reaction orders can be determined from the students’ results, and determine the rate equation and rate constant.

.Br2 is zero order .CH3COCH3 is first order .H+ is first order .linear negative gradient = zero order .straight line through 0,0 = first order .[H+] x 2 and rate is x 2 = first order k = rate/[CH3COCH3][H+]

This question is about organic reactions. Compound A is formed when ethanal is mixed with OH−(aq) ions, which act as a catalyst. The balanced equation is shown in reaction 6.1 below. i. Give the systematic name for compound A.

3-hydroxybutanal

how to find activation energy using a lnk 1/T graph

Ea = -gradient x 8.314 (J mol-1)

how to find pre-exponential factor on lnk 1/T graph

.find y intercept = ln A .do e^intercept on calc

how to find two-step mechanism for rate equations

RDS - use rate equation (balances for charge and num of atoms) .use the product that is not in the equation to form the other products in the equation

The rate constant, k, for this reaction is determined at different temperatures, T. Explain how the student could determine the activation energy, Ea, for the reaction graphically using values of k and T

.plot graph using K and 1/T .measure gradient .Ea = -gradient x 8.314

how to find Kc

.use ICE method to find equilbrium moles .divide equilibrium moles by vol to find conc .plug into equation

how to find Kp

.find mole fraction of each by dividing moles by total moles .find partial pressure by timing mole fraction by total pressure .plug partial pressure into equation

How to find Ka

[H+][A-]/[HA]

how to find pH using H+

-log^[H+]

how to find [H+] using pH

10^-pH

how to find Kw

[H+] x [OH-] .always 1x10^-14 mol^2 dm^-6

how to calculate the pH of an strong acid

.find M of acid = conc .M of acid = M of H+ in acid .plug it into -log^[H+]

how to find pH of an strong base

.find M of base .M of base = M of OH- .1x10^-14/M = [H+] .plug into -log^[H+]

how to find pH of a weak acid

[H+] = square root ( Ka x [HA] )

how to find pH buffers

pKa + log([A-]/[HA]) .pKa = -log(Ka)

Healthy human blood needs to be maintained at a pH of 7.40 for the body to function normally. *Carbonic acid, H2CO3, is a weak acid which, together with hydrogencarbonate ions, HCO3 −, acts as a buffer to maintain the pH of blood. The pKa value for the dissociation of carbonic acid is 6.38. Explain, in terms of equilibrium, how the carbonic acid–hydrogencarbonate mixture acts as a buffer in the control of blood pH, and calculate the [HCO3 −] : [H2CO3] ratio in healthy blood.

.addition of H+ shifts equilibrium to the left .addition od OH- shifts to the right .find Ka via 10^-6.38 .find [H+] via 10^-7.4 .find [HCO3]/[H2CO3] = Ka/[H+] .find ratio

Explain the relative resistance to chlorination of benzene compared to cyclohexene

.electrons cyclohexene are localised .electrons in benzene are delocalised .electron density in cyclohexene is higher and so is more susceptible to electrophillic attack

benzene + Cl mechanism

AlCl3 + Cl2 --> AlCl4- + Cl+ .arrow from benzene ring to the Cl+ .break ring where Cl is attached to and give it a positive charge .arrow from C-H bond to the broken part .chlorobenzene + H+ .H+ + AlCl4- --> AlCl3 + HCl

Describe, in terms of orbital overlap, the similarities and differences between the bonding in the Kekulé model and the delocalised model of benzene.

similar: .overlap of p-orbitals .pi bond system above and below the ring diff: .kekule has alternating pi bonds but delocalised has a pi ring system

* Many organic reactions use electrophiles as reagents. Explain the role of electrophiles in organic chemistry. Your answer should include one reaction of an aliphatic compound and one reaction of an aromatic compound, including relevant mechanisms.

.draw alkene + bromine mechanism .draw benzene and Cl mechanism with the AlCl3 + Cl2 --> AlCl4- + Cl+ AlCl4- + H+ --> AlCl3 + HCl .electrophile are electron pair acceptors

Explain why phenol is nitrated more readily than benzene.

.a pair of electrons from O from the hydroxyl group delocalises into the pi ring system .this makes phenol more electron dense than benzene and so more susceptible to electrophile attack

This question is about the chemistry of aromatic compounds. Benzoic acid can be nitrated by concentrated nitric acid in the presence of concentrated sulfuric acid as a catalyst, as shown in Equation 17.1. The organic product of this reaction is 3-nitrobenzoic acid. i. Outline the mechanism for this nitration of benzoic acid. Show how H2SO4 behaves as a catalys

.same as the chlorine one .HNO3 + H2SO4 --> H2O + HSO4- + NO2+ .H+ + HSO4- --> H2SO4

A chemist carries out the reaction in Equation 17.1 using 4.97 g of benzoic acid. The chemist obtains 3-nitrobenzoic acid as an impure solid. The chemist purifies the solid to obtain 4.85 g of 3-nitrobenzoic acid. Describe a method to obtain a pure sample of 3-nitrobenzoic acid from the impure solid, determine the percentage yield and check its purity

.recrytallisation .dissolve impure in minimum vol of hot water .cool solution and filter solid .wash with cold water and dry percentage yield = n(product)/n(reactant) x100

conditions for bromination of benzene

Br2 and AlBr3

conditions for the reduction of NO2 into NH2 on benzene

Sn and HCl

Another student attempts the same synthesis but carries out reduction before bromination. The student was surprised to find that two structural isomers of 3-bromophenylamine had been formed instead of the desired organic product. Explain this result and suggest the structures of the two isomers that formed

NH2 is 2,4 directing

nucleophillic addition of NaBH4/HCN with aldehydes/ketones mechanism

.H-/CN- nucleophile .delta positive and negative C and O .arrow from nucleophile to C .arrow from C=O bond to O .O is now negative and nucleophile attatchs on .arrow from O to H on a water molecule(H+ for HCN) .arrow from H-O bond to O on water .hydroxyl group where the O was

why is addition of CN cold as shit

.it adds an additonal C to the compound

Ester formation via CA

.CA + alcohol using a acid catalyst .forms water in the process alkylYL caOATE

ester formation via anhydride

.same as the CA but forms a CA instead of water

hydrolysis of esters

heat with aqueous alkali = Salt + H2O heat with aqueous acid = CA and alcohol

formation of acylchloride

CA + SOCl2

acylchloride reactions

+ water ---> CA + HCl +alcohol --> ester + HCl +amine ---> amide + HCl

how to form amines

.haloalkane + NH3 (ethanol) ---> amine + HX .nitrobenzene (Sn/HCl) .amines accept lone pair to make the H a positive

amide reaction

.CA and amine .remove the OH from CA and H from amine and bond the C and N .forms water aswel

how to name amides

N-amine groupYL CAamide e.g N-ethylbutanamide

chyal carbon

.C bonded to 4 different groups