Exam Questions I've Gotten Wrong
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Chlorine gas can be added to cold, dilute alkaline solution to form bleach. Write the equation for this reaction.
Cl2 + 2NaOH –> NaClO + NaCl + H2O
A student bubbles chlorine gas through aqueous potassium iodide. A reaction takes place. State what the student would observe.
yellow/orange/brown
CaCO3 –> reaction 2 –> CaO. What type of reaction is reaction 2?
thermal decomposition
What is meant by the term base?
Accepts H+ ions
(d) A student prepares a solution of calcium nitrate from calcium carbonate. What reagent would the student need to use? Write the equation for the reaction
HNO3 CaCO3 + 2HNO3 –> Ca(NO3) + H2O + O2
Avogadro’s constant
6.02x10^23
Draw a diagram showing hydrogen bonding with two H2O molecules
Two H2O molecules with delta + at H and delta - at O, and two lone pairs on each O, hydrogen bond from a H to a lone pair on the O of another molecule
State and explain two anomalous properties of ice
Lower density than water as molecules held apart by hydrogen bonds Relatively high melting point as hydrogen bonds strong
What intermolecular force is present in PH3?
Permanent dipole dipole interaction
BF3 bond angle?
120’
• Diphenylethanedione is a pale yellow colour, which disappears when it is reduced. The colour results from the arrangement of the delocalised π-bond electrons. Explain what is meant by the term delocalised π-bond electrons. (2)
delocalised electrons electrons are spread over more than two atoms AW (1) π-bond formed by overlap of p-orbitals/ diagram to show (1)
4-Methylphenylamine can be manufactured from benzene in three stages Describe how benzene could be converted by these three stages into 4-methylphenylamine. Include the structures of the intermediate compounds A and B. State the reagents and conditions. Give a balanced equation for each stage. (12)
methylation stage (can come anywhere) CH3Cl / CH3Br (1) AlCl3 / FeBr3 etc. (1) equation – e.g. C6H6 \+ CH3Cl → C6H5CH3 \+ HCl (1) intermediate name or unambiguous structure (1) 4 marks intermediates and equations will vary if methylation is done after nitration or reduction nitration stage (conc) H2SO4 (1) (conc) HNO3 (1) equation – e.g.: C6H5CH3 \+ HNO3 → C6H4 (CH3 )NO2 \+ H2O (1) intermediate – name or unambiguous structure (1) 4 marks Plymstock School 9 reduction stage tin/iron (1) HCl (1) equation – e.g.: C6H4 (CH3 )NO2 \+ 6[H] → C6H4 (CH3 )NH2 \+ 2H2O or with H+ also on left to give C6H4 (CH3 )NH3 \+ (1) 3 marks allow other suitable reducing agents: Quality of Written Communication mark for a well organised answer with the three stages clearly distinguished and sequenced (1) 1 mark
• Hydroxyethanal, HOCH2CHO, is sometimes referred to as the ‘first sugar’ as it is the simplest possible molecule that contains both an aldehyde group and an alcohol group. (ii) Outline the mechanism for this reduction. Use curly arrows and show any relevant dipoles. (4)
curly arrow from H– to Cδ+ dipoles and curly arrow from C=O bond to O ALLOW curly arrow to C even if dipole missing or incorrect intermediate curly arrow from intermediate to H δ+ in H2O/ H+ and if H2O is used it must show the curly arrow from the O–H bond to the O lone pairs are not essential
• Chloral hydrate is broken down in the body after several hours. One reaction is oxidation to trichloroethanoic acid. Complete the equation for this reaction below. (1)
CCl3CH(OH)2 + [O] → CCl3COOH + H2O (1)
• In this question, one mark is available for spelling, punctuation and grammar. Tollens’ reagent can be used to identify the aldehyde group in cinnamaldehyde. • Describe how you would make Tollens’ reagent and carry out this test in the laboratory. • Explain what happens to both the Tollens’ reagent and the cinnamaldehyde in this reaction. Identify the organic product. (8)
method silver nitrate (1) ammonia / ammoniacal (1) warm / heat (1) silver (mirror) / brown ppt forms (1) explanation silver ions reduced / Ag+ \+ e– → Ag (1) aldehyde oxidised to a carboxylic acid (1) correct structure – eg C6H5CHCHCOO– /COOH (1) quality of written communication mark for correct spelling, punctuation and grammar in at least two sentences (1)
• Suggest two reasons why standard enthalpy changes of combustion determined experimentally are less exothermic than the calculated theoretical values. (2)
Any two from the following: Heat released to the surroundings ALLOW heat loss Incomplete combustion OR incomplete reaction OR not everything burns IGNORE reference to evaporation Non-standard conditions
• In the vapour state, hydrogen and iodine undergo the following reaction. H2(g) + I2(g) 2HI(g) reaction 2.1 Write an equation, including state symbols, for the bond enthalpy of I − I.
I-I(g) → 2I(g)
(ii) Magnesium reacts with dilute acids. Describe what you would expect to see when magnesium ribbon is added to an excess of dilute hydrochloric acid. (2)
Fizzes OR bubbles OR gas produced OR effervescing DO NOT ALLOW ‘carbon dioxide gas produced’ DO NOT ALLOW ‘hydrogen produced’ without ‘gas’ Mg dissolves OR Mg disappears OR a solution is formed ALLOW ‘it for Mg’ IGNORE Mg reacts IGNORE temperature change IGNORE steam produced
• An ore of strontium contains strontium carbonate, SrCO3. To obtain metallic strontium, • the SrCO3 is converted into strontium oxide, SrO; • SrO is then reduced to produce strontium. (i) Suggest how strontium carbonate is converted into strontium oxide. (1)
heat
(i) State which two elements from the first twenty elements of the modern Periodic Table are not arranged in order of increasing atomic mass. (1)
K and Ar
(ii) Explain why increasing the concentration of H2O2(aq) increases the rate of decomposition. (2)
More crowded particles OR more particles per (unit) volume ALLOW particles are closer together DO NOT ALLOW ‘area’ instead of ‘volume’ IGNORE ‘more concentrated particles’ more collisions per second OR more frequent collisions ALLOW collisions more often OR increased rate of collision OR collisions are more likely OR there is a greater chance of collisions ‘More collisions’ is not sufficient
(iv) Explain why the straight chain isomer of C10H22 (which is usually used as a jet fuel) is converted by the petroleum industry into its branched chain isomers. (1)
Branched chains have more efficient combustion
Suggest a type of reactant that could be used to remove the HCl from the CH2CHCl monomer. (1)
alkali
In the past, hydrogen peroxide was manufactured by reacting barium peroxide, BaO2, with ice-cold dilute sulfuric acid. BaO2(s) + H2SO4(aq) → BaSO4(s) + H2O2(aq) This method required the disposal of poisonous barium compounds. Nowadays, hydrogen peroxide is manufactured using hydrogen gas, oxygen from the air and a substance called anthraquinone. stage 1 H2 + anthraquinone → anthraquinol stage 2 O2 + anthraquinol → H2O2 + anthraquinone Compare the manufacture of H2O2 from hydrogen and oxygen with the manufacture from barium peroxide described in (i). Explain the advantages of the manufacture of H2O2 from hydrogen and oxygen. (3)
Any three from the following: Oxygen comes from air IGNORE hydrogen comes from the air No poisonous materials formed OR no poisonous materials involved IGNORE harmful No waste products formed OR atom economy is 100% ALLOW higher atom economy Anthraquinone is regenerated OR recycled OR used again OR Anthraquinone acts as a catalyst