Predictions for Chemistry 2014 HSC? (3 Viewers)

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seventhroot

gg no re
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enigma_1 said:
I don't get the point of lurking :/

Isn't it like a waste of time lol
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I think they're thinking we have some sort of information that will give us an advantage

engima; next cryptic message: apfe fnue eoraw rnuwfsr sfoenta qmwowo
 
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GOsie

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enigma_1 said:
Someone can answer this:

Describe a local catchment area and potential sources of contamination to the catchment (3 marks)
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The Warragamba system is a catchment area in Sydney that collects and stores water for purification at the Prospect water filtration plant. Whilst this dam provides water to a large number of people in Sydney, it has to potential to be contaminated, making the water temporarily undrinkable.

The water may become turbid if surface runoff and groundwater collects particles from bushlands in the catchment area. This typically occurs after heavy rainfall.
The mining of minerals can cause high levels of dissolved ions, this also typically occurs from heavy rainfall.

Water runoff from agricultural land may lead to a rise in the level of microbes living in the water. This occurred in Sydney in the 1990s, where cryptosporidium and giardia contaminated the dam, making it not suitable for drinking.


No idea :/
 
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seventhroot

gg no re
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faisalabdul16 said:
long responses + multiple choice is going to destroy me
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faisalabdul16 said:
The troposphere is within the sea level to 10km range. Here temperatures are at its lowest in comparison to the other spheres and this is where nitrogen is the predominant gas, making up 78% of the atmosphere, followed by oxygen (20%) and then argon. The troposphere is where pollutant gases may be formed through human activity such as ozone which is dangerous as it is an irritant, however in the stratosphere (second atmospheric layer) ozone is of a benefcial advantage to us humans as it forms a barrier, preventing strong UV rays from entering into the troposphere and causing cataracts along with an increase in skin cancer. Stratosphere is approximately 15-50km above sea level. The mesosphere is 50-85km where there is barely any gases but has a few gas particles that would not exist in the previous spheres, and the temperature is higher than that of the stratosphere and troposphere because here there are strong UV rays and no ozone to shield it. Thermosphere as its name suggests is the hottest 85km +, barely any gases or particles present due to the heat.
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no need to snake m9
 
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GOsie

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faisalabdul16 said:
Why is complete combustion favoured over incomplete? 3 marks
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Complete combustion is typically preferred over incomplete combustion, as the products of complete combustion tend to be safer for the environment and society.

In the complete combustion of octane,

C8H18 + 25/2O2 --> 8CO2 + 9H2O

25/2 moles of oxygen are used in the reaction. However the products are H2O and CO2. Neither product is toxic and whilst CO2 contributes to global warming, it is a more favourable product than in incomplete combustion.


In the incomplete combustion of octane,

C8H18 + 5O2 --> CO +7 C + 9H2O (one example of the reaction)

Only 5 moles of oxygen are used in the reaction. However, CO is formed, which is a toxic gas and very harmful for humans, and C is formed, which is a black sooty substance that is messy and harmful for the environment as it can land on plants and prevent photosynthesis.

Therefore despite CO2 being a product of complete combustion, it is still favourable over CO and C which comes from incomplete combustion.
 
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faisalabdul16

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tommoo said:
Can you please show me the working to get HCL concentration?
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<img src="http://latex.codecogs.com/gif.latex?\text{Concentration&space;of&space;sodium&space;carbonate}=&space;\frac{1.314}{105.99&space;\textup{x}&space;0.25}&space;\\&space;\\&space;Na_2CO_3&space;&plus;&space;2HCl&space;\rightarrow&space;2NaCl&space;&plus;&space;CO_2&space;&plus;&space;H_2O&space;\\&space;\text{Volume&space;of&space;sodium&space;carbonate&space;=&space;0.02345L}\\&space;\\n=cv&space;\therefore&space;n&space;=&space;\frac{1.314\textup{x}0.02345}{105.99\textup{x}0.25}\\&space;\\&space;\text{Ratio&space;of&space;sodium&space;carbonate&space;moles&space;to&space;HCl&space;is&space;1&space;to&space;2,&space;therefore&space;moles&space;of&space;HCl&space;is&space;double&space;moles&space;of&space;sodium&space;carbonate}&space;\\&space;c&space;=\frac{n}{v}" title="\text{Concentration of sodium carbonate}= \frac{1.314}{105.99 \textup{x} 0.25} \\ \\ Na_2CO_3 + 2HCl \rightarrow 2NaCl + CO_2 + H_2O \\ \text{Volume of sodium carbonate = 0.02345L}\\ \\n=cv \therefore n = \frac{1.314\textup{x}0.02345}{105.99\textup{x}0.25}\\ \\ \text{Ratio of sodium carbonate moles to HCl is 1 to 2, therefore moles of HCl is double moles of sodium carbonate} \\ c =\frac{n}{v}" />

And then sub in values, remember n of HCl = double of sodium carbonate
 
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