NCEA Level 1 Chemistry (90932) 2012 Assessment Schedule

NCEA Level 1 Chemistry (90932) 2012 — page 1 of 6

Assessment Schedule – 2012 Chemistry: Demonstrate understanding of aspects of carbon chemistry (90932) Evidence Statement

Q Evidence Achievement Merit Excellence

ONE • Correct structure of • Links the (a) ethanol. conditions of fermentation to (Accept appropriate condensed or stick structures.) the conversion of glucose into (b) Fermentation involves the conversion of a solution of glucose molecules into ethanol and carbon ethanol. • Describes some dioxide in warm, anaerobic conditions using yeast as a catalyst. conditions of fermentation.

C6H12O6  2CH3CH2OH + 2CO2 • or C6H12O6  2C2H5OH + 2CO2 ONE balanced • TWO chemical unbalanced • States the products equation. (c) Ethanol undergoes complete combustion (with sufficient oxygen) to produce carbon dioxide and equations. of fermentation. water.

C2H5OH + 3O2  2CO2 + 3H2O • States that complete combustion occurs. (d) Complete combustion produces CO , which is a greenhouse gas. CO contributes to the greenhouse 2 2 • Lists products of effect, which leads to an increase in the amount of infra-red radiation trapped in the atmosphere. complete • Links the An increase in the concentration of CO2 on Earth is believed to lead to global warming and issues combustion. product of • Evaluates the around climate change. Some of the issues include extreme weather events, melting of ice at the poles, effect of a and decreased biodiversity. complete combustion to a product of The greenhouse effect is responsible for the Earth’s average temperature and is one of the reasons life • States a valid effect named complete exists on this planet. of combustion on the environmental combustion on environment (Water vapour, H2O gas, has also been shown to contribute to the greenhouse effect. When clouds are . effect. the environment. present in the atmosphere, more infra-red radiation is trapped.) NCEA Level 1 Chemistry (90932) 2012 — page 2 of 6

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No response or no 1a 3a 4a 5a 2m 3m 2e 2e relevant evidence. with minor error / with TWO omission balanced equations. NCEA Level 1 Chemistry (90932) 2012 — page 3 of 6

TWO Cracking is a thermal decomposition reaction using heat and / or a catalyst to vaporise a • Describes a condition of larger alkane and break its bonds to produce a smaller alkane and an alkene. cracking. • Explains the cracking Long chained hydrocarbons don’t flow as well, and are difficult to ignite (because process. bigger molecules don’t vaporise as easily), so they are less efficient fuels than shorter • Identifies large fractions as chained hydrocarbons. being inefficient as fuels

• Explains the An alkane and an alkene are produced. Since the number of carbon and hydrogen atoms cracking process does not change, 2 alkanes cannot be made (as there would be 2 H atoms short). • Links long chained which includes • Identifies an alkane and an Eg hexane hydrocarbons to a demonstrating an alkene as the products of feasible reason for understanding of cracking. not being used as a why it happens fuel. (large alkanes not EITHER useful) with valid Uses: uses for the Butane is used as a fuel in lighters, propellant in aerosol cans and is (mixed with products and an propane and) used to make LPG. understanding of why alkenes are Ethene is used to make ethanol and in polymerisation reactions to make polyethene. • States a use for the alkane produced in the • Explains why an OR produced. process. alkene is produced.

Uses: • States a use for the alkene produced. Propane is (mixed with butane and) used to make LPG. Propene is used in polymerisation reactions to make polypropene.

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No response or no 1a 2a 3a 4a 2m 3m e e relevant evidence. with minor error / minor omission NCEA Level 1 Chemistry (90932) 2012 — page 4 of 6

THREE (a) • Correct names for both alkanes.

• Correct structures for both alkanes.

(b) As the number of carbon atoms in alkanes increases, the boiling point increases. As the • States the trend for boiling • Links increasing size and boiling point of mass of the molecules increases, more energy is needed to separate molecules / particles to point. change state. This factor causes the boiling points to rise. alkanes to increased need for energy to (Note: as the size of the molecule increases so does the strength of the intermolecular separate the forces between the molecules. This means more energy is required to overcome the molecules / particles. intermolecular forces to allow a change in state. Candidates may use intermolecular forces in their answer correctly, though this aspect is outside of the scope of the standard.)

Oil floats on top of the water because it is insoluble in water (immiscible), so will not dissolve in it. Because the water molecules are more attracted to each other than they are • Explains why oil and (c) to oil molecules, a layer of oil forms on top of the water. (Candidates may say oil is less water are immiscible / dense than water, but this is outside the scope of standard, so it cannot be expected in the • States that oil is insoluble in insoluble in each • Explanation answer.) (less dense than) water. other OR links oil outlines The oil remains for a long time because it is insoluble in water, so the water cannot remaining for a long properties of oil disperse it. It is also a saturated / unreactive molecule so difficult to remove with other time to its lack of related to BOTH chemicals. (Candidates could say oil does not evaporate, due to the large size of the reactivity. observations. molecules, but again this is outside the scope of the standard.)

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No response or 1a 2a 3a 4a 1m 2m e e no relevant with minor error evidence. NCEA Level 1 Chemistry (90932) 2012 — page 5 of 6

FOUR • Draws and names ethene. (a)

• States a product of incomplete combustion. • Links ONE effect of • Explains TWO (b) Incomplete combustion produces C (soot) which can be inhaled and cause respiratory incomplete effects of problems and damage the heart. Soot is a carcinogen. CO can also be produced which is • States a valid effect on human combustion products incomplete a poisonous gas as it can replace oxygen’s position in red blood cells and cause death. health. to effects on human combustion health. products on human health. (c) LDPE and HDPE are both light, insoluble in water and have high chemical resistance. These properties make both of them suitable for storing food or drinks, as they won’t react with the food or drinks, and they are light, making them easy to carry. Links the flexibility • Explanation that LDPE is more flexible with its polymer chains loosely packed together, so it is suitable property of the polymer compares and for use as plastic food wrap, which needs to be flexible to wrap around any shaped food • Identifies TWO properties of to polymer chain contrasts at least (or food on plates) to store it. LDPE or HDPE in connection packing to explain their THREE HDPE is less flexible with its chains tightly packed together, so it is suitable to use to to its given use. difference of function. properties of each make plastic bottles, which need to be rigid enough to support the liquid drink that is polymer with stored in them. reference to the (Candidates are not required to know about branched chain hydrocarbons or inter given use. molecular forces.) • Links the lack of reactivity to the • Relates lack of Polythene is non-biodegradable because the single bonded hydrocarbon (alkane) chains (d) • Recognises that polythene is environment that reactivity to do not react (the strong covalent bonds between atoms need a lot of energy to be broken) not chemically reactive OR is breaks it down OR to strong covalent thus it can’t be broken down by chemicals in the environment (or decomposer a saturated hydrocarbon / has the type of bond. bonds / saturated organisms). strong covalent bonds. hydrocarbon and non- biodegradability in the environment.

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No response or no 1a 2a 3a 4a 2m 3m 2e 3e relevant evidence. NCEA Level 1 Chemistry (90932) 2012 — page 6 of 6

Judgement Statement

Achievement Achievement Not Achieved Achievement with Merit with Excellence Score range 0 – 9 10 – 16 17 – 24 25 – 32