Although how they were produced is not completely understood, petroleum and natural gas were most likely formed from the remains of marine organisms that lived approximately 500 million years ago. Petroleum is a thick, dark liquid composed mostly of compounds called hydrocarbons that contain carbon and hydrogen only. (Carbon is unique among elements in the extent to which it can bond to itself to form chains of various lengths.)

The table which follows gives the formulae and names for several common hydrocarbons. Natural gas, usually associated with petroleum deposits, consists mostly of methane, but it also contains significant amounts of ethane, propane, and butane. The composition of petroleum varies somewhat, but it consists mostly of hydrocarbons having chains that contain from 5 to more than 25 carbons. To be used efficiently, the petroleum must be separated into fractions by boiling. The lighter molecules (having the lowest boiling points) can be boiled off, leaving the heavier ones behind.

The commercial uses of various petroleum fractions are shown in the next table.

The petroleum era began when the demand for lamp oil during the Industrial Revolution outstripped the traditional sources: animal fats and whale oil. In response to this increased demand, Edwin Drake drilled the first oil well in 1859 at Titusville, Pennsylvania. The petroleum from this well was refined to produce kerosene (fraction C10–C18), which served as an excellent lamp oil. Gasoline (fraction C5–C10) had limited use and was often discarded.

However, this situation soon changed. The development of the electric light decreased the need for kerosene, and the advent of the “horseless carriage” with its gasoline-powered engine signaled the birth of the gasoline age. As gasoline became more important, new ways were sought to increase the yield of gasoline obtained from each barrel of petroleum. William Burton invented a process at Standard Oil of Indiana called pyrolytic (high-temperature) cracking. In this process, the heavier molecules of the kerosene fraction are heated to about 700 °C, causing them to break (crack) into the smaller molecules of hydrocarbons in the gasoline fraction.

As cars became larger, more efficient internal combustion engines were designed. Because of the uneven burning of the gasoline then available, these engines “knocked,” producing unwanted noise and even engine damage. Intensive research to find additives that would promote smoother burning produced tetraethyl lead, (C2H5)4Pb, a very effective “antiknock” agent.

The addition of tetraethyl lead to gasoline became a common practice, and by 1960, gasoline contained as much as 3 grams of lead per gallon. As we have discovered so often in recent years, technological advances can produce environmental problems. To prevent air pollution from automobile exhaust, catalytic converters have been added to car exhaust systems. The effectiveness of these converters, however, is destroyed by lead.

The use of leaded gasoline also greatly increased the amount of lead in the environment, where it can be ingested by animals and humans. For these reasons, the use of lead in gasoline has been phased out, requiring extensive (and expensive) modifications of engines and of the gasoline refining process.

B 1.2 - List the main uses of at least three fractions obtained from the fractional distillation of petroleum.

Uses should include fuels, petrochemicals, lubricants. Refer to SO A 2.5.

Fractional Distillation of Crude Oil

The fundamental separation process in refining petroleum is fractional distillation (next diagram). Practically all crude petroleum that enters a refinery goes to distillation units, where it is heated to temperatures as high as 370 to 425°C and separated into fractions. Each fraction contains a mixture of hydrocarbons that boils within a particular range.

Fractional distillation of petroleum. The lighter, more volatile fractions are removed from higher up the column; the heavier, less volatile fractions are removed from lower down.

Excessive amounts of solid residue and other long chain hydrocarbons are usually produced during fractional distillation of crude oil. Cracking breaks them into more useful molecules with shorter chains and also produces ethene.Thermal cracking uses high temperature and pressure to split long chain alkanes into short chain alkanes and alkenes. Hydrogen is a useful byproduct.Catalytic cracking uses low pressure, high temperature and zeolite catalysts to split long chain alkanes in to fractions used to make petrol, together with arenes (aromatic hydrocarbons containing the benzene ring).

Some Recent CSEC Past Paper Questions And AnswersLinks to the past papers covered below were working as of September 2017 and are:January 2016 P2: No online source known at this time.June 2015 P2: No online source known at this time.January 2015 P2: https://goo.gl/RuQdgmJune 2013 P2: No online source known at this time.Questions which follow are based on theory required for SS B 1.1 -1.3.January 2016 P2 Q5 (a) - (c)5(a) Petroleum.5(b) Fraction: Kerosene. Use: Jet fuel.Fraction: Lubricating oil. Use: Lubricants (for machines).5(c)(i) The breakdown of long chain hydrocarbon molecules into shorter chain molecules.5(c)(ii) Catalytic cracking uses a catalyst and relatively lower temperatures. Thermal cracking uses no catalyst and relatively higher temperatures.CXC's comments on this question are now shown below.

June 2015 P2 Q1 (a)(i)1(a)(i) Natural gas and petroleum.CXC's comments on this question are now shown below.

Wednesday, March 1, 2017

1(a) A
standard solution is one whose concentration is accurately known.

1(b) Mass of sample = 3.16 g

1(c)(i) Final
volumes:

Titration
1: 25.60 cm3

Titration
2: 26.30 cm3

Titration
3:24.50 cm3

1(c)(ii)Volume
used:

Titration
1: 24.60 cm3

Titration
2: 24.25 cm3

Titration
3: 24.35 cm3

1(c)(iii) According
to the wording in this question, the student is required to use values from all three titrations to calculate the average volume used. This however, is not what should actually be done
inthelab.Correcttreatmentof
this data says that you should ignore Titration 1 and find the average of volumes used in Titrations 2 and 3. Bothversionsareshownhere. The one in which all
three values were used, is
in red and the other in green. Please ask your teacher at school whether they subscribe to the literal interpretation of this question (in red) or
not.

Average
volume used = 24.40 cm3

Average
volume
used = 24.30
cm3

1(c)(iv)0.000244 mol

0.000243
mol

1(d)(i)0.001220
mol

0.001215mol

1(d)(ii) 0.01220
mol

0.01215
mol

1(e) 1.85 g

1.85g

1(f)1.31 g

1.31 g

1(g) 0.07278
mol

0.07278mol

1(h)5.97which
is 6 to the nearest whole number.

5.97
which is 6 to the nearest whole number.

1(i)Thesolutiongoesfrompalegreentoverypalepink/purple.

1(j) The
unreacted potassium permanganate present show that the end point has been reached because its colour does not
disappear.

2(a)(i) Electrolysis
is defined as the chemical decomposition of an electrolyte by the passage of an electric current.

2(a)(ii) Electroplating
is the deposition of a metal on the cathode of an electrolytic cell, via the passage of an electric current,
if therightcombinationof electrolyte
and electrodes (or electrode system) is used.

2(a)(iii) The
extraction of reactive metals e.g. Na and Al from their ores/compounds.

Extraction of active non-metals
e.g. thehalogens, like Cl2 from NaCl(aq) using the diaphragm cell.

3(b)(i)
A polymer is a substance with (macro) molecules built up from many smaller repeating units, which are connected
by covalent bonds: -P-P-P-P-P- or – (P)n -.

3(b)(ii) Type
of polymerization: Addition polymerization.

Name
of polymer: Polypropene

Use
of polymer: In the manufacture of bottles and containers.

3(c)(i) The
functional group present is the ester linkage (group).

3(c)(ii) Type
of polymerization: Condensation polymerization.

Use
of polymer: Manufacture of automobile bodies.

3(c)(iii) Water
is the by-product formed in this polymerization reaction.

Question 4

4(a)An isotope is a
species of an element having a different mass number, but the same atomic number as another species of
the same element, due to a difference in
the number of neutrons in the nuclei.

For carbon-12, number of protons = 6, and mass
number, i.e. number of (protons
+ neutrons) = 12 therefore number of neutrons = (12-6) = 6.

For carbon-13, number of protons = 6, and mass
number, i.e. number of (protons +
neutrons) = 13 therefore number of neutrons = (13-6) = 7.

So carbon-12 and carbon-13 have the same number of protons (6)
and different numbers of neutrons (6 and
7 respectively). They are therefore isotopes of carbon.

4(b) Radiocarbon dating uses carbon-14.

Treatment of cancer uses cobalt-60

Tracing of blood flow and locating of
obstructions in the circulatory system uses
sodium-24.

4(c)(i) Period number = number of occupied electron
shells. Group number = number of outer
electrons. W is in period 2, group 7 and X is in period 3, group 2. X is a metal and W is
a non-metal. The bonding between them is ionic
bonding. W forms W- and X
forms X2+, so the
formula of the compound formed is XW2.

4(c)(ii) The compound will dissolve in water. This is
because it consists of positive and
negative ions whose charges result in ion-dipole attractions with water, a polar solvent. In reality, this compound, MgF2 is one of a small number of insoluble fluorides so the correct answer is
that it is insoluble in water, but a CSEC
student normally does not know how to explain why a compound is insoluble. I can only guess what would be done
in a case where this question was
answered correctly in terms of lattice and hydration enthalpies.

Question 5

5(a)Ammonia is a
colourless gas with a pungent odour.

5(b)(i)

5(b)(ii) 2NH4Cl(s) + Ca(OH)2(s)→ 2NH3(g) + CaCl2(aq) + 2H2O(l)

5(b)(iii) Ammonia gas is a weak base and will react, in
a neutralization reaction , with sulfuric
acid. Hence calcium oxide (CaO(s)) can be
used as the drying agent since CaO is basic
and will not react with/neutralize the ammonia gas.

5(d) Three harmful effects of excessive nitrates in
the environment are:

1. Eutrophication of water bodies results from
high nitrate content.

2. Nitrates in drinking
water is poisonous to humans, especially babies.

3. Nitrosamines, which have been found in
foods are carcinogenic and are thought to orignate from
nitrates.

Question 6

6(a)1. Water is a very
good solvent as it dissolves both ionic and covalent compounds. Since
chemical reactions occur much more readily when in solution, water is important
for metabolic processes such as digestion and respiration. The ability of water
to dissolve oxygen is necessary for the survival of aquatic life.

2. Water has a high specific heat capacity and
can absorb a large amount of heat without a large change in temperature. This
helps living organisms, which contain approximately 70% water, to maintain a
relatively constant body temperature.

6(b)(i) Ca2+(aq) + Na2CO3(aq)→ CaCO3(s) + 2Na+(aq)

6(b)(ii) Boiling can remove temporary hardness. The
soluble hydrogencarbonates decompose to form the insoluble carbonates. Boiling
therefore softens the water by removing the Ca2+ and Mg2+ ions
that were in solution:

M(HCO3)2(aq)→ MCO3(s) + H2O(l) + CO2(g)

Where M is Ca and/or
Mg.

6(c) Hard water is water that does not
readily form a lather with soap.

Soft water is water
that readily forms a lather with soap.

To distinguish between hard and soft water
samples, the following method can be used. Equal volumes of both samples are
added to identical test tubes and the test tubes labelled. 1 cm3 of soap solution is
added to both water samples and shaken for 30 seconds. The height of lather
produced by each sample is measured. The water sample giving the greater height
of lather is the soft water. The hard water may either give a lower height of
lather, or no lather at all depending on the degree of hardness.