Slides in this set
The alkanes make up an important series of hydrocarbons. They are well known because they are the
compounds in many fuels. The simplest alkane is methane.
Here are the names and structural formulas of the first three alkanes:
The alkanes with small molecules (up to 4 carbon
Methane atoms) are gases at room temperature, 4-7 carbon
atoms are liquid, and 17 or above carbon atoms are
All alkanes burn. The hydrocarbons burn in air, forming
Ethane carbon dioxide and water.
Alkanes do not react with acids or alkalis. The
hydrocarbons do not react because the C-C and C-H
bonds in the molecules are unreactive.
Alkanes do not mix with water. They are less dense, and
so form a layer on top of it.
The alkanes are oily. They do not dissolve in water or mix with it.…read more
The first three members of the alcohol series are methanol, ethanol and propanol. An alcohol can be seen as an
alkane with one it's hydrogen atoms replaced by an OH group.
One hydrogen atom replaced by an OH group
The attractive forced between molecules of alcohols are stronger than they are in alkanes. The presence of an
-OH group of atoms gives the molecules this greater tendency to cling together like water. However, the
attractions between the hydrocarbon parts are very weak, as in alkanes.
Similarly the OH in the molecules of methanol and ethanol freely mix with water, unlike alkanes, but alcohols
with longer hydrocarbon chains do not mix with water because the oiliness part dominates.
The OH group is the reactive part of an alcohol molecule. Chemists call it the functional group for alcohols.
All alcohols burn due to the hydrocarbon parts of their molecules.
Alcohols react with sodium in a similar way to water. Ethanol + sodium = sodium ethoxide + hydrogen…read more
The functional group (reactive part) in the molecules of organic acids is
The series of compounds with this reactive group are the carboxylic acids. The chemical names of the
compounds are related to the alkane with the same number of carbon atoms. The ending `ane' becomes `anoic
Oxidization of ethanol produces ethanoic acid, as shown below. The ethanol molecule loses one of it's
hydrocarbon chains and adopts the new functional group (stated above), to form ethanoic acid (a carboxylic
Carboxylic acids ionize to produce hydrogen ions when dissolved in water. Only the hydrogen atom attached to
the oxygen is reactive, and this is the atom that ionizes . They only ionize to a light extent, which means they
are weak acids.
Carboxylic acids show the characteristic reactions of acids with metals, alkalis and metal carbonates:
Acid + metal = salt + hydrogen
Acid + soluble hydroxide = salt + water
Acid + metal carbonate = salt + carbon dioxide + water
When ethanoic acid reacts with sodium hydroxide, the salt formed is sodium ethanoate.…read more
Esters are very common. Many sweet-smelling compounds in perfumes and food flavourings are esters.
An alcohol can react with a carboxylic acid to make esters. The reaction happens when the alcohol and acid is
warmed in the presence of a little sulfuric acid, which acts as a catalyst.
Ethanoic acid Methanol
Methyl ethanoate (ester) Water
An ester splits into an acid and an alcohol when it reacts with water. This is a very slow change when a
catalyst is not used, and chemists call this change hydrolysis. Hydrolysis of fats and oils (see next slide) by
heating with alkali produces soaps, which are the sodium or potassium salts of fatty acids.…read more
Fats and oils
The alcohol in fats and oils is glycerol. This is a compound with three OH groups.
The carboxylic acids in fats and oils are often called fatty acids. These are common
Compounds with a long hydrocarbon chain attached to a carboxylic acid group.
Chemically, the difference between fats and oils arises from the structure of the carboxylic acids. When all the
bonds in a carboxylic acid molecule are single bonds, chemists describe it as saturated. The molecule has as
much hydrogen as it can take. The molecule is straight, packs together easily, and is solid at room temperature.
Eg. Stearic acid
When there is a double bond in each molecule of a carboxylic acid, the molecule is unsaturated. The double
bond means the molecule is not straight, they do not pack together as easily, and are liquid at room temp.
Eg. Oleic acid…read more