What is hydrolysis in the context of halogenoalkanes?

Hydrolysis is a reaction in which water or an aqueous alkali breaks a bond, replacing the halogen with a hydroxide group to form an alcohol.

Why is aqueous NaOH used instead of water as the nucleophile in halogenoalkane hydrolysis?

Aqueous NaOH is used because the hydroxide ion (OH - ) carries a full negative charge , making it a stronger nucleophile than water, where oxygen only carries a partial negative charge.

What order of bond enthalpy correctly ranks C-X bonds in halogenoalkanes?

The correct order is C-F > C-Cl > C-Br > C-I. C-F has the highest bond enthalpy (strongest bond) and C-I has the lowest (weakest bond), so iodoalkanes hydrolyse fastest.

In Core Practical 4, three test tubes each containing ethanol and acidified .......... are set up in a .......... °C water bath before adding the halogenoalkanes.

In Core Practical 4, three test tubes each containing ethanol and acidified silver nitrate are set up in a 50 °C water bath before adding the halogenoalkanes.

What colour precipitates form when chloroalkane, bromoalkane, and iodoalkane are each hydrolysed in the presence of acidified silver nitrate?

Chloroalkane gives a white precipitate, bromoalkane gives a cream precipitate, and iodoalkane gives a yellow precipitate with acidified silver nitrate.

True or False? Fluoroalkanes hydrolyse rapidly at room temperature because fluorine is the most electronegative halogen.

False. Fluoroalkanes do not react at all. The C-F bond has the highest bond enthalpy of all C-X bonds, making it too strong to break under these conditions.

Why is the reaction mixture warmed in Core Practical 4?

The hydrolysis of halogenoalkanes is very slow at room temperature , so the mixture is warmed to increase the rate of reaction.

Which halogenoalkane produces a precipitate most slowly in the silver nitrate test, and why?

The chloroalkane produces a precipitate most slowly because the C-Cl bond has the highest bond enthalpy of the reactive C-X bonds, making Cl - ions the slowest to form.

True or False? Ethanol is included in the silver nitrate test tubes in Core Practical 4 to dissolve the halogenoalkanes.

True. Ethanol acts as a co-solvent to dissolve the halogenoalkanes, which are not miscible with water alone, ensuring the reactants mix properly.

What is reflux in the context of Core Practical 5?

Reflux is a technique in which a reaction mixture is heated in a flask fitted with a condenser that returns vapours back into the flask, preventing loss of volatile reactants or products and allowing extended heating.

What oxidising agent is used to oxidise ethanol in Core Practical 5?

Acidified potassium dichromate(VI) , K 2 Cr 2 O 7 (aq), is used as the oxidising agent.

What are the two organic products that can form when ethanol is fully oxidised in Core Practical 5?

Ethanol is first oxidised to ethanal (an aldehyde) and then further oxidised to ethanoic acid (a carboxylic acid).

In Core Practical 5, the ethanol is added .......... into the reflux condenser and the pear-shaped flask is initially cooled in .......... before heating.

In Core Practical 5, the ethanol is added drop wise into the reflux condenser and the pear-shaped flask is initially cooled in iced water before heating.

Why must an electric heater or water bath be used in Core Practical 5 rather than a naked flame?

Ethanol is flammable, so using a naked flame creates a risk of fire or explosion. An electric heater or water bath provides safe, controlled heating.

True or False? Anti-bumping granules are added to the pear-shaped flask in Core Practical 5 to speed up the oxidation reaction.

False. Anti-bumping granules are added to promote smooth, even boiling and prevent sudden violent boiling (bumping), not to speed up the reaction.

Why is the pear-shaped flask cooled in an iced water bath before the reaction in Core Practical 5?

The flask is cooled before heating begins because the acidified potassium dichromate(VI) is added first and the reaction is exothermic; cooling prevents premature reaction and controls the addition of ethanol.

True or False? Distillation is used after reflux in Core Practical 5 to purify the oxidation product.

True. Distillation is used after reflux to separate and purify the product (ethanal or ethanoic acid) from the reaction mixture based on differences in boiling point.

What colour change is observed in the acidified potassium dichromate(VI) solution during the oxidation of ethanol?

The solution changes from orange (Cr 2 O 7 2- ) to green (Cr 3+ ) as the dichromate(VI) ions are reduced while oxidising the ethanol.

What is a separating funnel used for in Core Practical 6?

A separating funnel is a piece of apparatus used to separate two immiscible liquid layers, allowing the denser aqueous layer to be drained from the bottom tap while retaining the organic layer above.

What reagent is added to 2-methylpropan-2-ol to produce 2-chloro-2-methylpropane in Core Practical 6?

Concentrated hydrochloric acid is added to 2-methylpropan-2-ol to produce 2-chloro-2-methylpropane.

Why must pressure be released regularly when shaking the separating funnel in Core Practical 6?

Concentrated hydrochloric acid is volatile and releases hydrogen chloride gas , which builds up pressure inside the funnel. Regular release prevents the stopper being expelled and reduces risk of exposure to toxic fumes.

In Core Practical 6, .......... solution is added to the separating funnel to remove acidic impurities, and then .......... is added to the organic layer in a conical flask to remove water.

In Core Practical 6, sodium hydrogen carbonate solution is added to the separating funnel to remove acidic impurities, and then magnesium sulfate is added to the organic layer in a conical flask to remove water.

Why is the separating funnel left to stand for 20 minutes in Core Practical 6?

The funnel is left for 20 minutes to allow sufficient time for the nucleophilic substitution reaction between 2-methylpropan-2-ol and concentrated HCl to reach a reasonable yield, with gentle shaking every 2 minutes to maintain contact between the layers.

True or False? In Core Practical 6, the organic layer is the lower layer in the separating funnel after the reaction.

False. The organic layer (2-chloro-2-methylpropane) is less dense than the aqueous layer and therefore sits as the upper layer in the separating funnel.

What safety precaution is essential when using concentrated hydrochloric acid in Core Practical 6 and why?

The practical must be carried out in a fume hood because concentrated HCl is volatile and releases toxic hydrogen chloride gas rapidly when the container is opened.

What temperature range is collected during the final distillation step in Core Practical 6, and what does this represent?

The distillate is collected in the range 47–53 °C , which corresponds to the boiling point range of 2-chloro-2-methylpropane , allowing separation of the pure product from impurities.

True or False? Magnesium sulfate is added to the organic layer in Core Practical 6 because it reacts with water to form a hydrate, removing water from the product.

True. Magnesium sulfate is a drying agent that absorbs water by forming a hydrated salt (MgSO 4 ·7H 2 O), leaving the organic product dry before distillation.

What is qualitative analysis in chemistry?

Qualitative analysis is a set of experimental techniques used to identify the chemical composition of a sample by detecting the presence or absence of specific ions or functional groups, rather than measuring their quantity.

What reagent is added to test for ammonium ions (NH 4 + ) and what is the positive result?

Sodium hydroxide (NaOH (aq)) is added and the mixture is heated gently. A positive result is that damp red litmus paper turns blue in the presence of the ammonia gas produced.

What reagents are used to test for sulfate ions (SO 4 2- ) and what is the positive result?

The sample is first acidified with dilute hydrochloric acid , then a few drops of barium chloride solution are added. A white precipitate of barium sulfate (BaSO 4 (s)) is the positive result.

When testing for carbonate ions (CO 3 2- ), dilute hydrochloric acid is added to the sample and the gas produced is bubbled through .......... which turns .......... if carbon dioxide is present.

When testing for carbonate ions (CO 3 2- ), dilute hydrochloric acid is added to the sample and the gas produced is bubbled through limewater which turns milky (cloudy) if carbon dioxide is present.

Why is dilute hydrochloric acid added before barium chloride solution when testing for sulfate ions?

Dilute HCl is added first to remove any carbonate ions present in the sample. Carbonates would also produce a white precipitate with barium chloride, giving a false positive result.

True or False? In Core Practical 7, a solid sample must be dissolved in deionised water before test tube reactions can be performed.

True. Ion tests require the ions to be in aqueous solution so they are free to react with the added reagents. Solid samples must first be dissolved in deionised water .

What ionic equation represents the reaction when testing for ammonium ions with sodium hydroxide?

NH 4 + (aq) + OH - (aq) → NH 3 (g) + H 2 O (l) The ammonium ion reacts with the hydroxide ion to produce ammonia gas and water.

True or False? Hydrogencarbonate ions (HCO 3 - ) produce the same gas as carbonate ions when reacted with dilute hydrochloric acid.

True. Both CO 3 2- and HCO 3 - react with HCl to produce carbon dioxide gas , which turns limewater milky. The equations differ but the observable outcome is the same.

What apparatus is used to transfer the gas formed in the carbonate ion test into the limewater?

A bung with a delivery tube is attached to the test tube as soon as the acid is added, transferring the carbon dioxide gas produced into a separate test tube of limewater .

A LevelChemistryEdexcelFlashcards4. Core Chemistry PracticalsInorganic & Organic Chemistry Core Practicals

Inorganic & Organic Chemistry Core Practicals (Edexcel A Level Chemistry): Flashcards

Exam code: 9CHO

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FrontHydrolysis of Halogenoalkanes
What is hydrolysis in the context of halogenoalkanes?

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What is hydrolysis in the context of halogenoalkanes?
Hydrolysis is a reaction in which water or an aqueous alkali breaks a bond, replacing the halogen with a hydroxide group to form an alcohol.
Why is aqueous NaOH used instead of water as the nucleophile in halogenoalkane hydrolysis?
Aqueous NaOH is used because the hydroxide ion (OH^-) carries a full negative charge, making it a stronger nucleophile than water, where oxygen only carries a partial negative charge.
What order of bond enthalpy correctly ranks C-X bonds in halogenoalkanes?
The correct order is C-F > C-Cl > C-Br > C-I. C-F has the highest bond enthalpy (strongest bond) and C-I has the lowest (weakest bond), so iodoalkanes hydrolyse fastest.
In Core Practical 4, three test tubes each containing ethanol and acidified .......... are set up in a .......... °C water bath before adding the halogenoalkanes.
In Core Practical 4, three test tubes each containing ethanol and acidified silver nitrate are set up in a 50 °C water bath before adding the halogenoalkanes.
What colour precipitates form when chloroalkane, bromoalkane, and iodoalkane are each hydrolysed in the presence of acidified silver nitrate?
Chloroalkane gives a white precipitate, bromoalkane gives a cream precipitate, and iodoalkane gives a yellow precipitate with acidified silver nitrate.
True or False?
Fluoroalkanes hydrolyse rapidly at room temperature because fluorine is the most electronegative halogen.
False.
Fluoroalkanes do not react at all. The C-F bond has the highest bond enthalpy of all C-X bonds, making it too strong to break under these conditions.
Why is the reaction mixture warmed in Core Practical 4?
The hydrolysis of halogenoalkanes is very slow at room temperature, so the mixture is warmed to increase the rate of reaction.
Which halogenoalkane produces a precipitate most slowly in the silver nitrate test, and why?
The chloroalkane produces a precipitate most slowly because the C-Cl bond has the highest bond enthalpy of the reactive C-X bonds, making Cl^- ions the slowest to form.
True or False?
Ethanol is included in the silver nitrate test tubes in Core Practical 4 to dissolve the halogenoalkanes.
True.
Ethanol acts as a co-solvent to dissolve the halogenoalkanes, which are not miscible with water alone, ensuring the reactants mix properly.
What is reflux in the context of Core Practical 5?
Reflux is a technique in which a reaction mixture is heated in a flask fitted with a condenser that returns vapours back into the flask, preventing loss of volatile reactants or products and allowing extended heating.
What oxidising agent is used to oxidise ethanol in Core Practical 5?
Acidified potassium dichromate(VI), K₂Cr₂O₇ (aq), is used as the oxidising agent.
What are the two organic products that can form when ethanol is fully oxidised in Core Practical 5?
Ethanol is first oxidised to ethanal (an aldehyde) and then further oxidised to ethanoic acid (a carboxylic acid).
In Core Practical 5, the ethanol is added .......... into the reflux condenser and the pear-shaped flask is initially cooled in .......... before heating.
In Core Practical 5, the ethanol is added drop wise into the reflux condenser and the pear-shaped flask is initially cooled in iced water before heating.
Why must an electric heater or water bath be used in Core Practical 5 rather than a naked flame?
Ethanol is flammable, so using a naked flame creates a risk of fire or explosion. An electric heater or water bath provides safe, controlled heating.
True or False?
Anti-bumping granules are added to the pear-shaped flask in Core Practical 5 to speed up the oxidation reaction.
False.
Anti-bumping granules are added to promote smooth, even boiling and prevent sudden violent boiling (bumping), not to speed up the reaction.
Why is the pear-shaped flask cooled in an iced water bath before the reaction in Core Practical 5?
The flask is cooled before heating begins because the acidified potassium dichromate(VI) is added first and the reaction is exothermic; cooling prevents premature reaction and controls the addition of ethanol.
True or False?
Distillation is used after reflux in Core Practical 5 to purify the oxidation product.
True.
Distillation is used after reflux to separate and purify the product (ethanal or ethanoic acid) from the reaction mixture based on differences in boiling point.
What colour change is observed in the acidified potassium dichromate(VI) solution during the oxidation of ethanol?
The solution changes from orange (Cr₂O₇^2-) to green (Cr³⁺) as the dichromate(VI) ions are reduced while oxidising the ethanol.
What is a separating funnel used for in Core Practical 6?
A separating funnel is a piece of apparatus used to separate two immiscible liquid layers, allowing the denser aqueous layer to be drained from the bottom tap while retaining the organic layer above.
What reagent is added to 2-methylpropan-2-ol to produce 2-chloro-2-methylpropane in Core Practical 6?
Concentrated hydrochloric acid is added to 2-methylpropan-2-ol to produce 2-chloro-2-methylpropane.
Why must pressure be released regularly when shaking the separating funnel in Core Practical 6?
Concentrated hydrochloric acid is volatile and releases hydrogen chloride gas, which builds up pressure inside the funnel. Regular release prevents the stopper being expelled and reduces risk of exposure to toxic fumes.
In Core Practical 6, .......... solution is added to the separating funnel to remove acidic impurities, and then .......... is added to the organic layer in a conical flask to remove water.
In Core Practical 6, sodium hydrogen carbonate solution is added to the separating funnel to remove acidic impurities, and then magnesium sulfate is added to the organic layer in a conical flask to remove water.
Why is the separating funnel left to stand for 20 minutes in Core Practical 6?
The funnel is left for 20 minutes to allow sufficient time for the nucleophilic substitution reaction between 2-methylpropan-2-ol and concentrated HCl to reach a reasonable yield, with gentle shaking every 2 minutes to maintain contact between the layers.
True or False?
In Core Practical 6, the organic layer is the lower layer in the separating funnel after the reaction.
False.
The organic layer (2-chloro-2-methylpropane) is less dense than the aqueous layer and therefore sits as the upper layer in the separating funnel.
What safety precaution is essential when using concentrated hydrochloric acid in Core Practical 6 and why?
The practical must be carried out in a fume hood because concentrated HCl is volatile and releases toxic hydrogen chloride gas rapidly when the container is opened.
What temperature range is collected during the final distillation step in Core Practical 6, and what does this represent?
The distillate is collected in the range 47–53 °C, which corresponds to the boiling point range of 2-chloro-2-methylpropane, allowing separation of the pure product from impurities.
True or False?
Magnesium sulfate is added to the organic layer in Core Practical 6 because it reacts with water to form a hydrate, removing water from the product.
True.
Magnesium sulfate is a drying agent that absorbs water by forming a hydrated salt (MgSO₄·7H₂O), leaving the organic product dry before distillation.
What is qualitative analysis in chemistry?
Qualitative analysis is a set of experimental techniques used to identify the chemical composition of a sample by detecting the presence or absence of specific ions or functional groups, rather than measuring their quantity.
What reagent is added to test for ammonium ions (NH₄⁺) and what is the positive result?
Sodium hydroxide (NaOH (aq)) is added and the mixture is heated gently. A positive result is that damp red litmus paper turns blue in the presence of the ammonia gas produced.
What reagents are used to test for sulfate ions (SO₄^2-) and what is the positive result?
The sample is first acidified with dilute hydrochloric acid, then a few drops of barium chloride solution are added. A white precipitate of barium sulfate (BaSO₄ (s)) is the positive result.
When testing for carbonate ions (CO₃^2-), dilute hydrochloric acid is added to the sample and the gas produced is bubbled through .......... which turns .......... if carbon dioxide is present.
When testing for carbonate ions (CO₃^2-), dilute hydrochloric acid is added to the sample and the gas produced is bubbled through limewater which turns milky (cloudy) if carbon dioxide is present.
Why is dilute hydrochloric acid added before barium chloride solution when testing for sulfate ions?
Dilute HCl is added first to remove any carbonate ions present in the sample. Carbonates would also produce a white precipitate with barium chloride, giving a false positive result.
True or False?
In Core Practical 7, a solid sample must be dissolved in deionised water before test tube reactions can be performed.
True.
Ion tests require the ions to be in aqueous solution so they are free to react with the added reagents. Solid samples must first be dissolved in deionised water.
What ionic equation represents the reaction when testing for ammonium ions with sodium hydroxide?
NH₄⁺ (aq) + OH^- (aq) → NH₃ (g) + H₂O (l)
The ammonium ion reacts with the hydroxide ion to produce ammonia gas and water.
True or False?
Hydrogencarbonate ions (HCO₃^-) produce the same gas as carbonate ions when reacted with dilute hydrochloric acid.
True.
Both CO₃^2- and HCO₃^- react with HCl to produce carbon dioxide gas, which turns limewater milky. The equations differ but the observable outcome is the same.
What apparatus is used to transfer the gas formed in the carbonate ion test into the limewater?
A bung with a delivery tube is attached to the test tube as soon as the acid is added, transferring the carbon dioxide gas produced into a separate test tube of limewater.

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