Hydrocarbons Flashcards

All 18 cards in this deck

What is a hydrocarbon?

A compound containing hydrogen and carbon atoms only.

What are the molecular formulae of methane, ethane, propane and butane?

$\mathrm{CH_4}$, $\mathrm{C_2H_6}$, $\mathrm{C_3H_8}$, $\mathrm{C_4H_{10}}$

What is the general formula of an alkane?

$\mathrm{C_nH_{2n+2}}$

e.g. $n = 5$ gives $\mathrm{C_5H_{12}}$

Why are alkanes described as saturated hydrocarbons?

They contain hydrogen and carbon only, and all the carbon–carbon bonds are single bonds (no C=C).

What are the steps to draw the displayed structure of an alkane?

e.g. propane, $\mathrm{C_3H_8}$

1. Draw the carbon chain joined by single bonds: C–C–C
2. Add hydrogens so every carbon has 4 bonds: 3 H, 2 H, 3 H
3. Show every bond as a line, with no double bonds: $\mathrm{CH_3\!-\!CH_2\!-\!CH_3}$ with all C–H bonds drawn

True or false? $\mathrm{C_3H_6}$ is an alkane.

False. It fits $\mathrm{C_nH_{2n}}$, so it is an alkene (propene).

What are the molecular formulae of ethene, propene and butene?

$\mathrm{C_2H_4}$, $\mathrm{C_3H_6}$, $\mathrm{C_4H_8}$

What is the general formula of an alkene?

$\mathrm{C_nH_{2n}}$

e.g. $n = 4$ gives $\mathrm{C_4H_8}$

Why are alkenes described as unsaturated hydrocarbons?

They contain hydrogen and carbon only, and contain a C=C double bond between two carbon atoms.

What is the functional group of the alkenes?

The carbon–carbon double bond, C=C.

What are the steps to draw the displayed structure of but-1-ene?

e.g. $\mathrm{C_4H_8}$

1. Draw 4 carbons in a chain with the C=C between carbon 1 and carbon 2
2. Add hydrogens so every carbon has 4 bonds: 2 H, 1 H, 2 H, 3 H
3. Draw every bond as a line: $\mathrm{CH_2{=}CH\!-\!CH_2\!-\!CH_3}$ (but-2-ene has the C=C between carbons 2 and 3)

What is the balanced equation for the addition reaction of ethene with bromine?

$\mathrm{C_2H_4 + Br_2 \rightarrow C_2H_4Br_2}$

The C=C becomes a single C–C bond with one Br added to each carbon.

How do you use bromine water to distinguish between an alkane and an alkene?

e.g. propane and propene

1. Shake each hydrocarbon with bromine water, which is orange/yellow
2. Alkane (propane): colour stays orange/yellow — no reaction
3. Alkene (propene): bromine water turns colourless, because bromine adds across the C=C

What are the only products of the complete combustion of a hydrocarbon?

Carbon dioxide and water.

What is the balanced equation for the complete combustion of methane?

$\mathrm{CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O}$

What are the steps to balance an equation for complete combustion?

e.g. ethene, $\mathrm{C_2H_4}$

1. Put each carbon into a $\mathrm{CO_2}$: $2\mathrm{CO_2}$
2. Put each pair of hydrogens into an $\mathrm{H_2O}$: $2\mathrm{H_2O}$
3. Count the oxygen atoms on the right (6) and balance with $\mathrm{O_2}$: $\mathrm{C_2H_4 + 3O_2 \rightarrow 2CO_2 + 2H_2O}$

True or false? Complete combustion of a hydrocarbon is an oxidation reaction.

True. The carbon and hydrogen in the hydrocarbon are oxidised by oxygen to carbon dioxide and water.

True or false? Alkenes give different products from alkanes when burned completely.

False. Complete combustion of both alkanes and alkenes gives carbon dioxide and water only.