Reactions of Alkenes & Alcohols Flashcards

All 33 cards in this deck

What is the general formula for the homologous series of alkenes?

$C_nH_{2n}$

What is the functional group of the alkenes?

The carbon–carbon double bond, $C=C$

Name the first four members of the homologous series of alkenes.

Ethene, propene, butene, pentene

Why are alkene molecules described as unsaturated?

They contain a $C=C$ double bond, so they have two fewer hydrogen atoms than the alkane with the same number of carbon atoms.

True or false? $C_3H_8$ is an alkene.

False. $C_3H_8$ is an alkane (propane); the alkene with 3 carbon atoms is propene, $C_3H_6$.

In the displayed structural formula of ethene, what bonds are shown?

Two carbon atoms joined by a double bond ($C=C$), with two hydrogen atoms single-bonded to each carbon.

What are the products of the complete combustion of an alkene?

Carbon dioxide and water

Why do alkenes tend to burn in air with smoky flames?

Because incomplete combustion occurs, producing carbon (soot).

True or false? Alkenes burn in air with a cleaner, less smoky flame than alkanes.

False. Alkenes tend to burn with smokier flames because of incomplete combustion.

What are the steps to write a balanced equation for the complete combustion of an alkene?

e.g. ethene, $C_2H_4$

1. Write the products as $CO_2$ and $H_2O$: $C_2H_4 \rightarrow CO_2 + H_2O$

2. Balance carbon, then hydrogen: $\rightarrow 2CO_2 + 2H_2O$

3. Balance oxygen using $O_2$: $C_2H_4 + 3O_2 \rightarrow 2CO_2 + 2H_2O$

What happens to the carbon–carbon double bond in an addition reaction of an alkene?

e.g. ethene + bromine

Atoms add across the double bond, so it becomes a single carbon–carbon bond.

e.g. ethene + bromine gives $CH_2BrCH_2Br$ (dibromoethane).

What are the conditions and product for the reaction of an alkene with hydrogen?

e.g. ethene + hydrogen

A nickel catalyst (about 150 °C); the product is the corresponding alkane.

e.g. ethene + hydrogen $\rightarrow$ ethane

What are the conditions and product when an alkene reacts with steam?

e.g. ethene + steam

Steam with a catalyst, at high temperature and pressure; the product is an alcohol.

e.g. ethene + steam $\rightarrow$ ethanol

What is formed when an alkene reacts with chlorine, bromine or iodine, and what conditions are needed?

Two halogen atoms add across the double bond, giving a dihalogen compound (e.g. dichloro-, dibromo- or diiodo-); no catalyst or heating is needed.

True or false? When bromine reacts with ethene, both bromine atoms bond to the same carbon atom.

False. One bromine atom bonds to each of the two carbon atoms that were joined by the double bond.

What is the functional group of the alcohols?

$-OH$

Name the first four members of the homologous series of alcohols.

Methanol, ethanol, propanol, butanol

What happens when one of the first four alcohols reacts with sodium?

The sodium reacts and hydrogen gas is given off (fizzing).

What is produced when an alcohol reacts with an oxidising agent?

A carboxylic acid.

e.g. ethanol is oxidised to ethanoic acid.

What are the main uses of methanol, ethanol, propanol and butanol?

As fuels and as solvents; ethanol is also the alcohol in alcoholic drinks.

What conditions are used to produce ethanol by the fermentation of sugar solution with yeast?

Yeast added to sugar solution, kept warm (about 25–45 °C) and anaerobic (no oxygen/air).

What is the functional group of the carboxylic acids?

$-COOH$

Name the first four members of the homologous series of carboxylic acids.

Methanoic acid, ethanoic acid, propanoic acid, butanoic acid

What is formed when a carboxylic acid reacts with a carbonate?

A salt, water and carbon dioxide (seen as fizzing).

What happens when a carboxylic acid dissolves in water?

It ionises to form an acidic solution (pH less than 7).

What is formed when a carboxylic acid reacts with an alcohol, and what is needed?

An ester, using an acid catalyst.

e.g. ethanoic acid + ethanol $\rightarrow$ ethyl ethanoate

True or false? Both alcohols and carboxylic acids form acidic solutions when added to water.

False. Carboxylic acid solutions are acidic, but alcohols dissolve to give neutral solutions.

Why are carboxylic acids classed as weak acids?

They only ionise partially (incompletely) in water, because the ionisation reaction is reversible.

What is the equation for the ionisation of ethanoic acid in water?

$CH_3COOH(aq) \rightleftharpoons CH_3COO^-(aq) + H^+(aq)$

How does the pH of a carboxylic acid compare with that of a strong acid of the same concentration, and why?

The carboxylic acid has a higher pH, because it produces a lower concentration of hydrogen ions.

True or false? A weak acid and a dilute acid mean the same thing.

False. Weak means only partly ionised; dilute refers to a low concentration of acid.

Why does a carboxylic acid react more slowly with a carbonate than a strong acid of the same concentration?

It has a lower concentration of hydrogen ions, so there are fewer collisions per unit time.

True or false? When one of the first four alcohols burns completely in air, the products are carbon dioxide and water.

True. Alcohols are flammable and burn in air, releasing energy, e.g. $C_2H_5OH + 3O_2 \rightarrow 2CO_2 + 3H_2O$.