Alcohols (Edexcel A Level Chemistry): Flashcards
Exam code: 9CHO
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- FrontClassifying Alcohols
Define primary alcohol.
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Cards in this collection (28)
Define primary alcohol.
A primary alcohol is an alcohol in which the carbon atom bonded to the -OH group is also attached to only one other carbon atom (or alkyl group).
The functional group of alcohols is .......... and their general formula is .......... .
The functional group of alcohols is -OH and their general formula is CnH2n+1OH.
How are alcohols named using IUPAC nomenclature?
Alcohols are named by taking the corresponding alkane name and replacing the terminal -e with -ol. The suffix follows the pattern alkan-ol (e.g. ethanol, propan-1-ol).
Define secondary alcohol.
A secondary alcohol is an alcohol in which the carbon atom bonded to the -OH group is also attached to two other carbon atoms (or alkyl groups).
True or False?
Propan-2-ol is a secondary alcohol because the -OH group is on the second carbon.
True.
In propan-2-ol, the carbon bearing the -OH group is bonded to two other carbon atoms, which defines it as a secondary alcohol.
What is a diol and what suffix is used in its name?
A diol is an alcohol containing two -OH groups. The suffix -diol is added to the alkane name, with numbers indicating the positions of both hydroxyl groups (e.g. ethane-1,2-diol).
True or False?
2-methylpropan-2-ol is a tertiary alcohol.
True.
In 2-methylpropan-2-ol, the carbon bonded to the -OH group is attached to three other carbon atoms (all three methyl groups), classifying it as a tertiary alcohol.
Define tertiary alcohol.
A tertiary alcohol is an alcohol in which the carbon atom bonded to the -OH group is also attached to three other carbon atoms (or alkyl groups).
How do you determine whether an alcohol is primary, secondary or tertiary?
Count the number of carbon atoms directly bonded to the carbon carrying the -OH group: one carbon = primary, two carbons = secondary, three carbons = tertiary.
What are the oxidation products of a primary alcohol under mild and vigorous oxidation conditions?
Under mild conditions (distillation with addition), a primary alcohol is oxidised to an aldehyde. Under vigorous conditions (reflux with excess oxidising agent), the aldehyde is further oxidised to a carboxylic acid.
When acidified K2Cr2O7 oxidises an alcohol, the colour changes from .......... to .......... as the Cr2O72- ions are reduced to Cr3+ ions.
When acidified K2Cr2O7 oxidises an alcohol, the colour changes from orange to green as the Cr2O72- ions are reduced to Cr3+ ions.
What reagent is used to test for the -OH group in an unknown liquid, and what is the positive result?
Phosphorus(V) chloride (PCl5) is added to the liquid. A positive result is the production of steamy fumes of hydrogen chloride (HCl) gas, indicating the presence of the -OH group.
True or False?
Tertiary alcohols can be oxidised by acidified potassium dichromate(VI).
False.
Tertiary alcohols do not undergo oxidation because the carbon bearing the -OH group has no hydrogen atom attached to it, so there is nothing to remove during the oxidation process.
What is Tollens' reagent and what does a positive result look like?
Tollens' reagent is an ammoniacal silver nitrate solution used to distinguish aldehydes from ketones. A positive result is the formation of a silver mirror on the inside of the test tube when the reagent is warmed with an aldehyde.
True or False?
Heating under reflux is used when producing an aldehyde from a primary alcohol.
False.
To produce an aldehyde, distillation with addition is used so that the aldehyde is removed as soon as it forms. Heating under reflux would allow the aldehyde to be further oxidised to a carboxylic acid.
What reagent and conditions are used to dehydrate an alcohol to an alkene?
The alcohol is heated with concentrated phosphoric acid (H3PO4). The -OH group and a hydrogen from an adjacent carbon are eliminated, forming a C=C double bond and water.
What colour change is observed in Fehling's solution when warmed with an aldehyde?
The clear blue Fehling's solution becomes opaque and a red precipitate of copper(I) oxide (Cu2O) forms. This indicates the aldehyde has been oxidised to a carboxylic acid.
Secondary alcohols can be oxidised to form .......... only; they cannot be oxidised further because the carbonyl carbon in a ketone has no .......... atom attached to it.
Secondary alcohols can be oxidised to form ketones only; they cannot be oxidised further because the carbonyl carbon in a ketone has no hydrogen atom attached to it.
How are bromoalkanes made from alcohols in the laboratory?
The alcohol is warmed with a mixture of potassium bromide and 50% concentrated sulfuric acid. The KBr and H2SO4 first react to produce HBr, which then reacts with the alcohol to give the bromoalkane and water.
What is fractional distillation?
Fractional distillation is a technique used to separate two or more miscible liquids by heating the mixture and collecting each component as it boils, starting with the substance of lowest boiling point.
How is boiling point used to assess the purity of an organic liquid?
The measured boiling point of the liquid is compared to the data book value. A pure liquid boils at a sharp, fixed temperature — any significant deviation from the data-book value, or a broad boiling range, indicates the presence of impurities.
In solvent extraction, the desired organic product is removed from the reaction mixture using a solvent that is .......... with the original mixture and in which the product is .......... soluble.
In solvent extraction, the desired organic product is removed from the reaction mixture using a solvent that is immiscible with the original mixture and in which the product is more soluble.
True or False?
Anhydrous magnesium sulfate is used in solvent extraction to remove water from the organic layer.
True.
Anhydrous magnesium sulfate (MgSO4) is added to the organic layer after separating the layers. It absorbs water by forming a hydrate and is removed by gravity filtration.
What type of mixture is separated by simple distillation, and how does it work?
Simple distillation separates a liquid from a dissolved solid (or a pure liquid from a mixture). The solution is heated, the liquid evaporates, the vapour passes through a condenser and is collected as a pure liquid.
What is crystallisation as a purification technique?
Crystallisation is a technique used to purify a dissolved solid by dissolving it in hot solvent, allowing the saturated solution to cool slowly so that pure crystals form, then filtering, washing and drying them.
True or False?
In fractional distillation of ethanol and water, the mixture is heated to 100 °C to drive off the ethanol first.
False.
The mixture is heated to 78 °C (the boiling point of ethanol) so that ethanol distils first. Heating to 100 °C would boil the water, not selectively separate ethanol.
In crystallisation, the solution is tested for saturation by dipping a cold glass rod into it: if the solution is saturated, .......... will form on the rod.
In crystallisation, the solution is tested for saturation by dipping a cold glass rod into it: if the solution is saturated, crystals will form on the rod.
Why is it more efficient to use smaller volumes of solvent in multiple stages during solvent extraction?
Using smaller volumes in multiple stages removes more of the desired product overall than using the same total volume in one step, because each stage extracts a greater proportion of the remaining product.
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