Organic Chemistry Homework 3- Alcohols and Organic Acids
Name: ………………………………….. Marks: /
Class: …………………………………… Date:
Paper 2 [Structured and Free Response Questions]
Section A [Structured Questions]
1
Organic Chemistry Homework 3- Alcohols and Organic Acids
Name: ………………………………….. Marks: /
Class: …………………………………… Date:
Paper 2 [Structured and Free Response Questions]
Section A [Structured Questions]
1 Some information about some alcohols is given in the table.
name relative molecular boiling point, oC heat produced on
mass, Mr completely burning
one mole, kJ
methanol 32 65 720
ethanol 78 1370
60 97 2010
butanol 74 2670
pentanol 88 138
(a) Complete the table by
(i) adding the name of the other alcohol: propanol
(ii) calculating the missing relative molecular mass: 46
(iii) estimating the boiling point of butanol: 117ºC
(iv) estimating the heat produced on completely burning one mole of pentanol.
(b) Complete the equation for the complete combustion of butanol.
……..C4H9OH + 6O2 4CO2 + 5H2O ; ∆H = - 2670 kJ/mol
(c) Explain why the data for the heat produced in burning one mole increases down the
More strong bonds are formed in the products, so more heat energy is produced.
2 A list of formulas of several organic compounds is given below.
C2H5OH C5H10 C3H7COOH C8H18 C3H8
Choose from these formulas, the ones that fit the descriptions below.
(a) a compound that undergoes an addition reaction with steam
(b) a compound that has a pH less than 7 in water
(c) a compound that is oxidised by air to produce ethanoic acid
(d) one compound that is not a hydrocarbon
C2H5OH / C3H7COOH 
(e) two compounds which are in the same homologous series
C3H8 and C8H18 
(f) two compounds that react together to produce an ester
C2H5OH and C3H7COOH 
3 (a) The formula of a weak carboxylic acid can be represented by CnH2n+1CO2H (where
n is an integer).
(i) Explain the meaning of the term ‘weak acid’.
A weak acid is one that is only partially ionised when dissolved in water to
produce hydrogen ions. 
(ii) Suggest a test to distinguish between 2 mol/dm3 CH3COOH and 2 mol/dm3
HCl. State the observable change in this test and explain your answer.
Place a few drops of Universal indicator into equal volume of both acids in
separate test tubes. The Universal indicator will gives a red colour if the acid
is 2 mol/dm3 HCl, since dilute hydrochloric is a strong acid. The Universal
indicator will gives a orange/yellow colour if the acid is 2 mol/dm3
CH3COOH, since dilute ethanoic acid is a weak acid. 
(b) A carboxylic acid weighing 0.355 g was dissolved in about 20 cm3 of distilled
water in a conical flask. The resultant solution required 22.4 cm3 of 0.18 mol/dm3
sodium hydroxide for complete neutralization.
(i) the number of moles of sodium hydroxide used for the titration;
number of moles of sodium hydroxide = 22.4/1000 × 0.18
= 0.004032 mol
(ii) the relative molecular mass of the carboxylic acid;
number of moles of carboxylic acid = 0.004032 mol
thus, relative molecular mass, Mr, of the carboxylic acid = 0.355/0.004032
(iii) deduce the structural formula of the carboxylic acid.
The general formula of carboxylic acid is CnH2n+1COOH
n(12) + (2n+1) + 12 + 2(16) +1 = 88
the structural formula of the acid is
4 The structures of six compounds, A - F, are shown below.
A B C
H O H H H H H H
H C C O H H C C H C C C C H
H H H H H H H
D E F
H H H H H H
H C O C H H C C O H H C O C C H
O H H H H H H
(a) Use the letters A to F, to answer the following questions.
(i) Which compounds are isomers : A and D
(ii) Which compound reacts with sodium carbonate? A
(iii) Which compound is an unsaturated hydrocarbon? C
(iv) Which compound can be made by reacting an organic acid with an alcohol? D
(v) Which compound is formed by the oxidation of compound E? A
(b) Compound E is the second member of a homologous series. Write the formula of
the first member of this series.
(c) Compound F has molecular formula C3H8O. Draw the structure of another
compound with this molecular formula.
4 Some vegetable oils contain an organic acid called linoleic acid, which is unsaturated.
(a) What is meant by the term unsaturated?
An unsaturated compound is one which contains multiple bonds between carbon
atoms (e.g. C=C bond or C≡C bond), in which other atoms can be added to the
molecule by addition reaction.
(b) Name the reagent used and give the observation in a simple chemical test which
would confirm that
(i) linoleic acid is unsaturated.
Add linoleic acid into aqueous bromine in a test tube and shake.
If linoleic acid is unsaturated, the reddish-brown aqueous bromine will
(ii) linoleic acid is an acid:
Add a small piece of magnesium ribbon into a portion of linoleic acid in a test
If linoleic acid is an acid, effervescence will be observed, and the gas evolved will
extinguish a lighted splint with a ‘pop’ sound.
(c) Linoleic acid has molecular formula C17 H29COOH. How many C=C bonds are
present in one molecule of linoleic acid? Explain your answer.
number of C=C bonds:3 C=C bonds
explanation : The molecular formula of linoleic acid has 6 hydrogen atoms less than
a satu