Alkenes Flashcards

All 7 cards in this deck

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