Inorganic & Organic Chemistry Core Practicals (Edexcel International A Level (IAL) Chemistry): Flashcards
Exam code: YCH11
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List the C-X bond enthalpies in order from highest to lowest.
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List the C-X bond enthalpies in order from highest to lowest.
C-F > C-Cl > C-Br > C-I. The stronger the C-X bond, the slower the rate of hydrolysis.
What is hydrolysis of a halogenoalkane?
Hydrolysis is a reaction in which the C-X bond in a halogenoalkane is broken by a nucleophile (OH- or water), replacing the halogen with a hydroxyl group.
What reagent and conditions are used to hydrolyse a halogenoalkane in the laboratory?
Aqueous sodium hydroxide (NaOH) or potassium hydroxide (KOH) is used. The mixture is warmed, as the reaction is slow at room temperature.
True or False?
Fluoroalkanes undergo hydrolysis faster than iodoalkanes.
False.
Fluoroalkanes do not react at all because the C-F bond has the highest bond enthalpy of all C-X bonds. Iodoalkanes react the fastest.
How is acidified silver nitrate used to measure the rate of halogenoalkane hydrolysis?
Three test tubes in a 50°C water bath each contain ethanol and acidified silver nitrate. A different halogenoalkane is added to each, and the time for a precipitate to form is recorded. A shorter time indicates a faster rate of hydrolysis.
True or False?
The yellow precipitate forms the fastest in the silver nitrate hydrolysis test.
True.
The yellow precipitate is silver iodide (AgI), formed from iodoalkanes. The C-I bond has the lowest bond enthalpy, making it the easiest to break.
State the precipitate colours formed when chloro-, bromo- and iodoalkanes are hydrolysed with silver nitrate.
Chloroalkane: white precipitate (AgCl)
Bromoalkane: cream precipitate (AgBr)
Iodoalkane: yellow precipitate (AgI)
In the silver nitrate test, the .......... precipitate forms the slowest because the C-Cl bond has the highest bond enthalpy.
In the silver nitrate test, the white precipitate forms the slowest because the C-Cl bond has the highest bond enthalpy.
Why is OH- a better nucleophile than water in halogenoalkane hydrolysis?
OH- carries a full negative charge, making it a stronger nucleophile than water, where the oxygen only carries a partial negative charge (δ-).
What are the key steps in the synthesis of 2-chloro-2-methylpropane from 2-methylpropan-2-ol?
Measure 8 cm3 of 2-methylpropan-2-ol into a separating funnel
In a fume hood, add 20 cm3 of concentrated hydrochloric acid in small portions, releasing pressure after each addition
Stand for 20 minutes in the fume hood, shaking every 2 minutes
Drain the lower aqueous layer
Add sodium hydrogen carbonate solution to remove acidic impurities, then drain the aqueous layer
Add magnesium sulfate to dry the organic layer, then distil and collect at 47–53°C
What is a separating funnel?
A separating funnel is a piece of apparatus used to separate two immiscible liquid layers, allowing the unwanted (aqueous) layer to be drained away from the organic product.
Why is sodium hydrogen carbonate solution added during the synthesis?
Sodium hydrogen carbonate solution is added to remove acidic impurities from the organic layer. It neutralises any remaining hydrochloric acid.
Why is magnesium sulfate added to the organic layer?
Magnesium sulfate is a drying agent added to remove traces of water from the organic layer. Once the liquid is clear, it is decanted and ready for distillation.
In this synthesis, ..........cm3 of 2-methylpropan-2-ol is mixed with 20 cm3 of concentrated hydrochloric acid.
In this synthesis, 8 cm3 of 2-methylpropan-2-ol is mixed with 20 cm3 of concentrated hydrochloric acid.
What temperature range is used to collect the product by distillation?
The distillate is collected in the range of 47–53°C, which corresponds to the boiling point of 2-chloro-2-methylpropane.
True or False?
The fume hood window should be kept below the safety line to ensure the exhaust system works effectively.
True.
If the window is raised above the safety line, the exhaust system cannot draw in fumes effectively, allowing toxic gases to escape into the laboratory.
Why must a fume hood be used in this synthesis?
Concentrated hydrochloric acid is very volatile and releases hydrogen chloride gas at room temperature, which is toxic. A fume hood prevents exposure to harmful fumes.
Why must pressure be released regularly when using the separating funnel?
Concentrated hydrochloric acid is volatile and produces gas inside the funnel. If pressure is not released by opening the stopper regularly, the funnel may become pressurised and could be forced open.
What are the two oxidation products of propan-1-ol?
Propan-1-ol is first oxidised to propanal (an aldehyde) and, on further oxidation, to propanoic acid (a carboxylic acid).
Why must an electric heater or water bath be used instead of a Bunsen burner in this experiment?
Propan-1-ol is flammable, so naked flames must be avoided. An electric heater or water bath provides controlled heat without the risk of igniting the alcohol vapour.
What is reflux in organic synthesis?
Reflux is a technique in which a reaction mixture is heated in a flask connected to a condenser, so that vapours condense and return to the flask. It allows prolonged heating without loss of volatile reactants.
What is the oxidising agent used to oxidise propan-1-ol?
Acidified potassium dichromate(VI), K2Cr2O7 (aq), is used as the oxidising agent.
Why are anti-bumping granules added to the flask?
Anti-bumping granules are added to promote smooth, even boiling and prevent sudden violent boiling (bumping) during heating.
The propan-1-ol is added ..........into the reflux condenser using a pipette.
The propan-1-ol is added dropwise into the reflux condenser using a pipette.
State the key steps in the synthesis of propanal from propan-1-ol.
Add 20 cm3 of acidified potassium dichromate(VI) solution to a pear-shaped flask and cool in an ice bath
Set up reflux apparatus, keeping flask cool
Add anti-bumping granules
Slowly add 1 cm3 of propan-1-ol dropwise into the reflux condenser using a pipette
Remove the ice bath and allow to warm to room temperature
Heat for 20 minutes using an electric heater or water bath
Purify the product by distillation
State two hazards associated with propan-1-ol in this experiment.
Flammable: keep away from naked flames
Harmful: avoid skin contact and inhalation of vapour
True or False?
Primary alcohols are oxidised directly to carboxylic acids without forming an aldehyde intermediate.
False.
Primary alcohols are first oxidised to aldehydes. On further oxidation, the aldehyde is converted to a carboxylic acid.
What is the hazard associated with potassium dichromate(VI)?
Potassium dichromate(VI) is a strong oxidising agent. Spillages should be mopped up immediately with plenty of water to prevent fire risk and skin irritation.
Describe the test for ammonium ions (NH4+).
Add sodium hydroxide solution to the sample and warm gently. Hold damp red litmus paper near the mouth of the test tube. A positive result is shown by the paper turning blue, indicating the presence of ammonia gas.
What is a flame test?
A flame test is a technique used to identify metal ions by the distinctive colour they produce when heated strongly in a Bunsen flame.
Describe the test for carbonate ions (CO32-).
Add dilute hydrochloric acid to the sample. Bubble the gas produced through limewater using a delivery tube. A positive result is shown by the limewater turning milky, indicating the presence of carbon dioxide.
True or False?
Damp red litmus paper turns blue in the presence of ammonia gas.
True.
Ammonia is an alkaline gas, so it turns damp red litmus paper blue. This is the positive result for the ammonium ion test.
Describe the test for sulfate ions (SO42-).
Acidify the sample with dilute hydrochloric acid, then add aqueous barium chloride. A positive result is shown by a white precipitate of barium sulfate (BaSO4).
Carbon dioxide turns limewater ..........
Carbon dioxide turns limewater milky.
Why is dilute HCl added before barium chloride in the sulfate ion test?
Dilute HCl is added first to remove any carbonate ions that may be present. Carbonates would also form a precipitate with barium chloride, giving a false positive result.
Describe the procedure for carrying out a flame test.
True.
Nichrome and platinum are used because they are unreactive and do not produce their own flame colour, avoiding contamination of the test.
True or False?
A nichrome or platinum wire is used in flame tests because these metals are unreactive.
True.
Nichrome and platinum are used because they are unreactive and do not produce their own flame colour, avoiding contamination of the test.
Why must the wire loop be cleaned before a flame test?
The wire must be cleaned to avoid contamination from previous samples. If two or more ions are present, their colours will mix, making identification unreliable.
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