SPI Chemistry · Formula sheet

Carbon and Its Compounds formulas

2 formulas, 6 reference tables and 14 common traps for SPI Chemistry Carbon and Its Compounds, grouped by subtopic.

Carbon Bonding and Hydrocarbons

Covalent bonds and how to count them

Covalent bonds in an alkane

\text{bonds in } \mathrm{C}_n\mathrm{H}_{2n+2} = (n - 1) + (2n + 2) = 3n + 1

$n$ number of carbon atoms

Homologous series and isomers

Mass step in a homologous series

M_{\text{next}} = M + 14 \text{ u} \qquad \mathrm{CH_2} = 12 + 2 \times 1 = 14 \text{ u}

Allotropes of carbon

Allotrope	Each carbon bonds to	Structure	Key property
Diamond	4 carbons	Rigid three-dimensional network	Hardest natural substance, does not conduct
Graphite	3 carbons	Hexagonal layers, one above another	Soft, slippery, conducts electricity Graphite is the only one of the three that conducts.
Fullerene	3 carbons	Closed cage, $\mathrm{C_{60}}$ is a football shape	Separate molecules, not one giant network

Same atoms, different arrangements: that is what allotropes means.

Alkanes, alkenes, alkynes and rings

Family	General formula	Bonds	Example
Alkane	$\mathrm{C}_n\mathrm{H}_{2n+2}$	Single only	Methane $\mathrm{CH_4}$ , propane $\mathrm{C_3H_8}$
Alkene	$\mathrm{C}_n\mathrm{H}_{2n}$	One double bond	Ethene $\mathrm{C_2H_4}$ , propene $\mathrm{C_3H_6}$
Alkyne	$\mathrm{C}_n\mathrm{H}_{2n-2}$	One triple bond	Ethyne $\mathrm{C_2H_2}$ , propyne $\mathrm{C_3H_4}$
Cycloalkane	$\mathrm{C}_n\mathrm{H}_{2n}$	Ring of single bonds	Cyclohexane $\mathrm{C_6H_{12}}$ A ring has the same general formula as an alkene, but no double bond.
Cycloalkene	$\mathrm{C}_n\mathrm{H}_{2n-2}$	Ring with one double bond	Cyclohexene $\mathrm{C_6H_{10}}$
Benzene	$\mathrm{C_6H_6}$	Ring, alternate single and double bonds	Benzene

In a drawn ring, each corner is a carbon: count the double bonds to name it.

Common traps

Counting only the carbon-hydrogen bonds

The number of hydrogens is not the number of bonds. An alkane with

n

carbons also has

n - 1

carbon-carbon bonds, so the total is

3n + 1

Thinking carbon forms ions

Carbon neither loses nor gains 4 electrons. It shares them, so its compounds are covalent and do not conduct electricity.

Calling diamond a conductor because it is carbon

Diamond does not conduct: every valence electron is held in a bond. Graphite conducts because one electron per carbon is free.

Taking a ring for an alkene

Cyclohexane,

\mathrm{C_6H_{12}}

, fits

\mathrm{C}_n\mathrm{H}_{2n}

but has only single bonds, because its carbons close into a ring. Look at the structure, not just the formula.

Counting the single bonds next to a triple bond

A triple bond does not make every other bond triple. Butyne has four carbons, so besides its triple bond it has two carbon-carbon single bonds. Propyne has exactly one.

Saying isomers have the same structure

Isomers share the molecular formula only. Their structural formulae differ, and so do their properties.

Expecting the physical properties to stay the same

Down a homologous series the chemical properties stay similar, but the boiling point rises as the chain grows by each

\mathrm{CH_2}

Reactions, Ethanol and Ethanoic Acid

Learn this subtopic in the notes

Combustion, oxidation, addition and substitution

Reaction	Which compounds	Example
Combustion	All hydrocarbons	$\mathrm{CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O}$
Oxidation	Alcohols, then aldehydes	Ethanol to ethanoic acid, which turns blue litmus red
Addition	Unsaturated only	$\mathrm{C_2H_4 + H_2 \rightarrow C_2H_6}$ (nickel catalyst) Alkenes and alkynes add; alkanes cannot.
Substitution	Saturated hydrocarbons	$\mathrm{CH_4 + Cl_2 \rightarrow CH_3Cl + HCl}$ (sunlight)

Unsaturated means a double or triple bond: that is what lets a compound add.

Ethanol

Fact	Ethanol
Formula	$\mathrm{C_2H_5OH}$
Boiling point	About 78 °C (351 K)
With sodium	$\mathrm{2Na + 2C_2H_5OH \rightarrow 2C_2H_5ONa + H_2}$ The gas is hydrogen: it burns with a pop.
With hot concentrated sulphuric acid	Loses water to give ethene, $\mathrm{C_2H_4}$
Uses	Solvent, medicines such as cough syrups, fuel

Ethanol is the second member of the alcohols, after methanol.

Ethanoic acid

Reacts with	Products
Sodium hydroxide	$\mathrm{CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O}$
Sodium carbonate	$\mathrm{2CH_3COOH + Na_2CO_3 \rightarrow 2CH_3COONa + H_2O + CO_2}$ The fizzing is carbon dioxide: it turns lime water milky.
Blue litmus	Turns red
Ethanol (concentrated sulphuric acid)	Ethyl ethanoate, a sweet-smelling ester

Sodium ethanoate,

\mathrm{CH_3COONa}

, is the salt in every row that makes one.

Esters, saponification and soap

Reaction	Reactants	Products
Esterification	$\mathrm{CH_3COOH + C_2H_5OH}$ , with concentrated $\mathrm{H_2SO_4}$	$\mathrm{CH_3COOC_2H_5 + H_2O}$
Saponification	Ester + sodium hydroxide	Sodium salt of the acid + alcohol Saponification starts from an ester and an alkali.
Soap making	Oil or fat + sodium hydroxide	Soap + glycerol

Ethyl ethanoate,

\mathrm{CH_3COOC_2H_5}

, is the ester of ethanoic acid and ethanol.

Common traps

Expecting an alkane to add

Addition needs a double or triple bond to open. Alkanes are saturated, so with chlorine they substitute, and with hydrogen they do nothing.

Calling ethanol a hydrocarbon

A hydrocarbon contains only carbon and hydrogen. Ethanol,

\mathrm{C_2H_5OH}

, contains oxygen, so it is an alcohol, not a hydrocarbon.

Mixing up the boiling points

Ethanol boils at about 78 °C, water at 100 °C and ethanoic acid at about 118 °C. Ethanol is the lowest of the three.

Expecting carbon dioxide from sodium and ethanol

A metal such as sodium gives hydrogen gas with ethanol. Carbon dioxide comes from an acid reacting with a carbonate or a hydrogencarbonate.

Taking ethanoic acid for a strong acid

Ethanoic acid is weak: only a little of it splits into ions. At the same concentration its pH is higher than that of hydrochloric acid.

Saying the gas is hydrogen

An acid with a carbonate or a hydrogencarbonate gives carbon dioxide. Hydrogen comes from an acid with a reactive metal.

Swapping esterification and saponification

Acid + alcohol giving an ester is esterification. Ester + alkali giving a salt and an alcohol is saponification. One builds the ester, the other breaks it.

Carbon and Its Compounds formulas

Carbon Bonding and Hydrocarbons

Covalent bonds and how to count them

Homologous series and isomers

Allotropes of carbon

Alkanes, alkenes, alkynes and rings

Common traps

Reactions, Ethanol and Ethanoic Acid

Combustion, oxidation, addition and substitution

Ethanol

Ethanoic acid

Esters, saponification and soap

Common traps

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