AQA GCSE Chemistry Unit 1 Unofficial Mark Scheme 09/06/2015

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11Jason11
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Questions and Answers:

Elements
a)
What is the atomic number? Number of protons (1 Mark)

What is the mass number? Number of protons plus neutrons (1 Mark)

b)
Why doesn't an atom have any charge? This is because they have the same number of positively charged protons in the nucleus, as the number of negatively charged electrons in their shells. (2 Marks)

C)
The periodic tables groups? This is because they have the same number of electrons in their outermost shell (7 electrons in their outermost shell) and thus have similar chemical properties. (2 Marks)

d)
Tick the correct box: S (Sulphur) (1 Mark)

e)
Particles that include non-metal and metal: Ions (1 Mark)
Particles that include two non-metals: Molecules (1 Mark)

Limestone
a)
Limestone is calcium… carbonate (1 Mark)
Calcium oxide is produced through thermal… decomposition (1 Mark)
Calcium hydroxide is created by adding… water (1 Mark)
How can limestone be used to neutralize acids? It’s an alkali. (1 Mark)

b)
Line of best fit (In red) (2 Marks)













How could the accuracy be improved?
By repeating the step shown in figure 2, calculating an average (discarding anomalies). OR Decreasing the intervals between results being taken. (2 Marks)

Estimate the force needed for 0g from the graph? 45 (This value will slightly vary) (2 Marks)

Why isn't his prediction about the trend correct? Because after 400 grams, the force needed begins to decrease as for 700 grams, the force needed is 100 newtons. (3 Marks)

The earth
a)
Why are there so many theories? Lack of reliable evidence from the time. Also some evidence conflicts causing many theories. (1 Mark)
Change in the earth's surface and atmosphere: In the early atmosphere billions of years ago, it is thought that, due to intense volcanic activity, in the Earth’s atmosphere, there was a lot of carbon dioxide, water vapour and small proportions of methane and ammonia. However, over this changed. As the Earth’s atmosphere began to cool down, the water vapour in the air condensed to form oceans. This caused a lot of the carbon dioxide within the air to be dissolved into the water and thus removing a lot of it from the atmosphere. Moreover, a lot of the carbon within the water, overtime, became carbonate. This then formed parts of the shells and skeletons of the sea creatures within the ocean. When they died, they became sedimentary rocks, thus locking up a lot of the carbon. Furthermore, when algae and plants came into existence, they were able to undergo a process called photosynthesis. Photosynthesis is a process which encompasses Carbon Dioxide converting into Oxygen. This meant that, as the years went by, there was a reduction in amount of Carbon Dioxide and increase amounts of oxygen. As a result of all of this, the atmosphere is around 80% nitrogen and 20% oxygen, however there are small proportions of carbon dioxide, water vapour and noble gases. This number is changing. This because, from the exponential rapid population increase of the human population, fossil fuels – made up of carbon and dead, fossilised plants and animals – are being used to generate electricity. This means that, at the moment, the increase rate in these being burnt has resulting in an increase in Carbon Dioxide in our atmosphere. (6 Marks)





Metals
a)
Why was stage 2 (separation) necessary? This is so that the ore is concentrated meaning that the metal produced will be purified, ridding of any impurities found within the ore. This is why you are separating so that when the metal is extracted, no impurities will be within. (2 Marks)

b)
Why isn’t cast Iron suitable for pylons? Too brittle, easily brakes. (1 Mark)
Describe the process shown in the diagram (Cast Iron + Oxygen --> Waste gases + Steel) Cast iron is heated in a furnace in the presence of oxygen, so that it can form an alloy with carbon to produce steel. At the high temperature at the bottom of the furnace, carbon dioxide reacts with carbon to produce carbon monoxide. It is the carbon monoxide which is the main reducing agent in this part of the furnace. In the hotter parts of the furnace, the carbon itself also acts as a reducing agent. As the cast iron is heated, the carbon and, in some parts of the furnace, the carbon monoxide react with the cast iron entering the furnace to form the alloy steel. The temperature of the furnace is hot enough to melt the steel which trickles down to the bottom where it can be tapped off. (2 Marks)

c)
Why is aluminium more suitable for pylons compared to copper? Its less
dense, therefore lighter. (1 Mark)

From the periodic table, how can we tell that copper is a transition metal?
Aluminium is found in group three meaning it has only 3 electrons in its outermost shell. Moreover as it is in this certain group, its charges of its ions can have only one set charge. However copper is not in any numbered group but in group which is between group 2 and 3, meaning that copper can have ions with different charges and thus is a transition metal. Furthermore, within the group that it in, it is surrounded by only transition metals. (2 Marks)

How is copper extracted from Copper salts using iron?
As iron is more reactive than copper, the scrap iron can displace the copper within the copper ions so that the copper produced will be pure./Removes the impurities (2 Marks)










Oils
a)
How are fractions of oil separated? Crude oil enters a fractionating column is hot vapour which has been heated up to around 350°C. At the top of the column it is cooler and towards the bottom it is hotter. As the hydrocarbons within the crude oil all have different boiling points, the long chain hydrocarbons with the highest boiling points will be separating out the bottom of the column, the rest of the hydrocarbons rise up through the column as a hot vapour. When the hydrocarbons reach a certain temperature which is their boiling points, the gases will condense into their liquid forms and be separated into fractions. (4 Marks)

b)
Suspension of limestone: Sulfur dioxide and Nitrogen oxide are slightly acidic, they therefore react with Calcium Carbonate to produce a salt, water and carbon dioxide. This reduces the amount of Sulfur dioxide and Nitrogen oxide in the air, thus reducing levels of acid rain. (3 marks)

c)
C2H4 (1 Mark)
Draw the hydrocarbon (3 Marks)










How to smart polymers differ from normal polymers?
The change their properties when there are changes in the environment i.e. they react to heat and temperature. (1 Mark)









6. Vegetable Oils
a)
Why are vegetable oils useful for both fuels and in food? They contain a lot of energy. (1 Mark)

Why are vegetable oils more useful compared to water in cooking?
They have a high boiling point, thus they provide a lot of energy. (2 Marks)

State two process used in extracting vegetable oil from seeds?
Plant Material is crushed and the oil is removed by pressing or distillation; water and other impurities are removed. (2 Marks)

How to emulsifiers work?
Its head is hydrophilic and the tail is hydrophobic the emulsifier is negative charge.The ‘tail’ dissolves in the oil making tiny droplets. The surface of each oil droplet is charged by the ‘heads’ sticking out into the water. As the head is negatively charged, the like charges repel each other. This keeps them spread throughout the water, stopping the oil and water separating into two layers. (4 Marks)

Credit to @Harrywigman for helping
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11Jason11
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11Jason11
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isthatmatilda
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slight correction for the metals section: the iron displaces the copper itself not the impurities
btw the graphs aren't showing up?
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Palette
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I prefer Decklan's mark scheme, as it gives me a higher score and doesn't have unnecessary information.
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Lola1244
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Thanks so much for this! would I get error carried forward if graph was wrong so like on the conclusion if I used my graph values
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aadil10
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(Original post by 11Jason11)
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The line of best fit there doesn't ignore the anomalous result, but it should.
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username1942323
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(Original post by aadil10)
The line of best fit there doesn't ignore the anomalous result, but it should.
Which on the anomalous then

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sandvika
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(Original post by mediaya)
Which on the anomalous then

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You ignore the middle cross on the first line
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aadil10
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(Original post by mediaya)
Which on the anomalous then

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that graph is inaccurate but it was either the 2nd or 3rd point, not sure. 3 of the first 4 points lined up perfectly and 1 didn't, that was the anomalous result. When drawing a line of best fit you should ignore anomalous results
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sandvika
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"Its less dense, therefore lighter" Someone really wants their mark.... Also you got a few wrong
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orangeee22
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(Original post by 11Jason11)
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I think this graph is wrong. It said one of the results is anomalous, which is the third one, because if you plot a line with the first two to the fourth point all the points are exactly on the line, so you need to ignore it the third point.

Therefore the answer to the b) (iii) is 38, not 44
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Fatimah21
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Why are vegetable oils more useful compared to water in cooking?
They have a high boiling point, thus they provide a lot of energy. (2 Marks)
For this question, I wrote it has a high boiling point and I crossed it out and wrote that oil makes the food have a better taste
Would I still get the mark?
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11Jason11
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(Original post by Fatimah21)
Why are vegetable oils more useful compared to water in cooking?
They have a high boiling point, thus they provide a lot of energy. (2 Marks)
For this question, I wrote it has a high boiling point and I crossed it out and wrote that oil makes the food have a better taste
Would I still get the mark?
Yes better taste will get you a mark
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Tulpa Kalamack
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(Original post by aadil10)
that graph is inaccurate but it was either the 2nd or 3rd point, not sure. 3 of the first 4 points lined up perfectly and 1 didn't, that was the anomalous result. When drawing a line of best fit you should ignore anomalous results
Yep. The first three line up and the highest one is the anomaly. You can see this as a double check on a graph because neither of the lines will be near it.
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Fatimah21
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(Original post by 11Jason11)
Yes better taste will get you a mark
YESSSSSSSSSSS!!!!!!!
Thank you
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Tulpa Kalamack
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(Original post by Fatimah21)
Why are vegetable oils more useful compared to water in cooking?
They have a high boiling point, thus they provide a lot of energy. (2 Marks)
For this question, I wrote it has a high boiling point and I crossed it out and wrote that oil makes the food have a better taste
Would I still get the mark?
That is one of the two points made in the revision guides so probably yes.
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Tulpa Kalamack
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(Original post by Lola1244)
Thanks so much for this! would I get error carried forward if graph was wrong so like on the conclusion if I used my graph values
Probably. They said to mark your graph so if you did based on your lines you will likely get a mark.
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helloeveryone123
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For 'how could the accuracy be improved' could you have put by using smallers weights?&could you have said that aluminium is resistant to corrosion?
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Burning
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Ugh I hate my life, I put oxygen instead of sulfur because I though there was only 16 electrons. Damn cheap 2 marks that I threw away hope it doesn't affect my grade
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