Chemistry Unit 2 Revision: Homologous Series, Fuels, and Mole Calculations

Comprehensive revision flashcards covering homologous series, naming rules, structural formulas, fuels, gas tests, and mole/GFM calculations based on Chemistry Unit 2 mind maps.

What is the definition of a homologous series?

A family of hydrocarbons with the same general formula and similar chemical properties.

Why do the melting and boiling points increase within a homologous series as molecular size increases?

An increase in molecular size strengthens the intermolecular forces and therefore increases melting and boiling points.

What is the chemical test to distinguish between saturated and unsaturated hydrocarbons?

Add the compound to bromine water: no reaction indicates a saturated compound, while decolorisation indicates an unsaturated compound.

What distinguishes saturated hydrocarbons from unsaturated hydrocarbons structurally?

Saturated hydrocarbons contain carbon-carbon single bonds, whereas unsaturated hydrocarbons contain carbon-carbon double bonds.

What is the functional group of the alkene family?

Carbon-carbon double bonds ($C=C$).

How can an alkane be identified by its structure and its name?

By structure: it contains carbon-carbon single bonds. By name: it ends in -ane (e.g., pentane).

How can an alkene be identified by its structure and its name?

By structure: check if it has a double bond. By name: it ends with -ene (e.g., pentene).

How can a cycloalkane be identified by its structure and its name?

By structure: the structure is shaped in a ring. By name: it starts with cyclo- (e.g., cyclopentane).

What are the general formulas for alkanes, cycloalkanes, and alkenes?

Alkanes: $C_n H_{2n+2}$; Cycloalkanes: $C_n H_{2n}$; Alkenes: $C_n H_{2n}$.

How many bonds do carbon and hydrogen each need to form in order to become stable?

Carbon needs to form 4 bonds; hydrogen needs to form 1 bond.

What are the prefixes used for carbon compounds with 1 to 8 carbons?

1: meth-, 2: eth-, 3: prop-, 4: but-, 5: pent-, 6: hex-, 7: hept-, 8: oct-.

What is a common use for alkanes?

Fuels.

What is the shortened structural formula for propane?

$$CH_3CH_2CH_3$$

What is the shortened structural formula for hex-2-ene?

$$CH_3CH=CHCH_2CH_2CH_3$$

What is the shortened structural formula of cyclopentane?

A 5-carbon ring consisting of five $CH_2$ groups linked together.

What is the definition of a hydrocarbon?

A compound made up entirely of carbon and hydrogen atoms.

What is the test and positive result for oxygen gas?

It relights a glowing splint.

What is the test and positive result for hydrogen gas?

It burns with a squeaky pop.

What is the test and positive result for carbon dioxide gas?

It turns water into a milky cloudy color.

The mass of one mole of a substance is equal to what quantity?

The gram formula mass (GFM).

What are the three equations relating mass ($m$), number of moles ($n$), and gram formula mass ($GFM$)?

$m = n \times GFM$, $n = \frac{m}{GFM}$, and $GFM = \frac{m}{n}$.

What is the gram formula mass (GFM) of octane ($C_8H_{18}$)?

$114\,g$ (calculated as $(18 \times 1) + (8 \times 12) = 18 + 96 = 114\,g$).

What is the gram formula mass (GFM) of but-2-ene ($C_4H_8$)?

$56\,g$ (calculated as $(8 \times 1) + (4 \times 12) = 8 + 48 = 56\,g$).

What is the gram formula mass (GFM) of $C_{13}H_{28}$?

$184\,g$ (calculated as $(28 \times 1) + (13 \times 12) = 28 + 156 = 184\,g$).

How many moles are present in $28.5\,g$ of octane ($GFM = 114\,g$)?

$$n = \frac{m}{GFM} = \frac{28.5}{114} = 0.25\,\text{moles}$$

How many moles are present in $0.56\,g$ of but-2-ene ($GFM = 56\,g$)?

$$n = \frac{m}{GFM} = \frac{0.56}{56} = 0.01\,\text{moles}$$

How many moles are present in $920\,g$ of $C_{13}H_{28}$ ($GFM = 184\,g$)?

$$n = \frac{m}{GFM} = \frac{920}{184} = 5\,\text{moles}$$

What is the mass of $15\,\text{moles}$ of octane ($GFM = 114\,g$)?

$$m = n \times GFM = 15 \times 114 = 1710\,g$$

What is the mass of $3.25\,\text{moles}$ of but-2-ene ($GFM = 56\,g$)?

$$m = n \times GFM = 3.25 \times 56 = 182\,g$$

What is the mass of $0.02\,\text{moles}$ of $C_{13}H_{28}$ ($GFM = 184\,g$)?

$$m = n \times GFM = 0.02 \times 184 = 3.68\,g$$