Analysis test
1
/25
Name:
Halogenoalkanes can be made from alkenes according to the following reaction:
CH3CH=CH2
+
HCl

CH3CH2CH2Cl
4.20g of propene reacted with 50cm3 of 1 mol dm-3 of Hydrochloric acid. After the reaction
had finished, 1.96g of 1-chloropropane was made.
a) Identify the limiting reagent, show all your working
Mr of propene = 42 (1) Moles of propene = 0.1 (1) Moles of HCl = 0.05 (1) so HCl limiting
reagent
[3]
b) Calculate the % yield of 1-chloropropane
Moles 1-chloropropane = 0.025 (1) %yield = (0.025 / 0.05) x 100 = 50% (127%)
[2]
c) Calculate the atom economy of 1-chloropropane
Atom economy = (78.5 / 78.5) x 100 = 100%
[1]
2
A chemistry student was oxidising ethanol to ethanal according to reaction (A). Her
teacher suggested ethanol would oxidise further producing ethanoic acid according to
reaction (B):
-A
-B
a) The product was then run through a mass spectra and gave the spectra below:
Explain how mass spectra might work?
Ionisation (1) acceleration (1) deflection / time of flight (1) detection (1) time of flight /
magnitude of magnetic field is proportional to mass (1)
[5]
b) Identify the molecular ion peak
m/z = 60 (1)
[1]
c) Who was right? The teacher of the student? Explain your answer
Teacher (1) m/z = 60 which is Mr of ethanoic acid (1) if student was right would be m/z at
44 (1)
[3]
d) Write a chemical reaction to show how the molecular ion peak was formed
CH3COOH
+
e-

CH3COOH+
+ 2e-
CH3COOH+ (1) rest of equation (1)
[2]
e) Identify the fragment which is responsible for the peak at 15. Write a reaction to show
how that fragment was formed.
CH3+ (1) CH3COOH+  CH3+ + COOH Reactants (1) Products (1)
[3]
f) What other spectroscopic technique could used to distinguish between the 2 possible
products?
Infrared spectroscopy
[1]
g) Use the data sheet to predict what peaks would be present and absent in the 2
products
Ethanal: C=O 1680 – 1750 (1) no O-H peak at 2500 – 3300 (1)
Ethanoic acid: C=O 1680 – 1750 (1) Peak at O-H peak at 2500 – 3300 (1)
[4]