Hi can u check my response?
- Is qualitative an indirect evidence and quantitative a direct evidence
- Am i allowed to omit the spectator ions for carbonate, iron reaction (below)
- is it enough to know the effects of acid rain as the only qualitative evidence
-For "discuss" questions i dont need a concluding statement right ?
There has been an increase in the concentration of the oxides of nitrogen and sulfur in the atmosphere. Assess both the evidence to support this statement and the need to monitor these oxides 8 marks
Oxides of sulfur has increased in concentration from burning sulfide ores to extract metals CuS(s) + O2(g) -->Cu(s) + SO2(g) which releases SO2(g)
Whereas, acidic oxides of Nitrogen has increased mainly due to internal combustion engines and coal burning power stations.
N2(g) + O2(g) -->2NO(g)
2NO(g) + O2(g) -->2NO2(g)
These oxides the react with the water in the atmosphere:
SO2 (g) + H2O(l) -->H2SO3(aq)
2NO2(g) + H2O (l)-->HNO2(aq) + HNO3 (aq)
The evidence for the increase in these oxides comes from both direct of measurements of gas concentrations in the atmosphere and indirectly through effect of the increase in acid rain due to these oxides. The quantitative measurements are accurate and reliable due to the development of technologies in recent time. For eg. levels of SO2 and NO2 gases measured by analysing the gases trapped in bubbles of Antarctic ice which is a sample of the atmosphere from the past 200 years.
The indirect evidence comes from the effects of acid rain formed by these oxides. The acids H2SO3(aq) and HNO2(aq)/HNO3(aq) react and dissolves carbonates, which destructs historically important buildings and statues made of limestone and marble thus this becomes a record for the increase in levels of these oxides. 2H+(aq)+CaCO3(s)-->CO2(g) + H2O(l)+ Ca2+(aq) . Steel bridges and other steel structures also show evidence of damage due to acid rain since it reacts iron and dissolves it. 2H+(aq)+ Fe(s)-->H2(g)+Fe2+(aq). However, these evidences are less reliable as they could be resulted due to other oxides or factors.
It is vital to record the monitor and record increasing levels of pollution so that we will know when to act and reduce the levels of NOx and SO2 as they are respiratory irritants therefore can cause asthma and other respiratory diseases and thus have a devastating impact on population’s health. They also lead to formation of acid rain which will cause cuticle on leaves to strip off leading to degradation of forest.
Overall, the direct and indirect evidence both shows the increase in concentration of these oxides, however, they are not completely reliable as the concentration of oxides changes over time and they are not representative of all parts of the world.
Hey Amanda!
I will just start off answering your questions first:
1. Both qualitative and quantitative are direct evidences (not necessarily first-hand evidences though!). Qualitative requires you to describe this evidence. So for example in this case if you mentioned photochemical smog, you would need to account for this evidence and explain how this evidence affects monitoring oxide levels in the future. Quantitative evidence requires numbers, either from data that the question perhaps gives you in an exam or from data you've already known beforehand. Just making up some statistics here, for example you can say about 100000 tonnes of nitrogen oxides are contributed by internal combustion engines or 5000 tonnes of nitrogen oxides are measured to be released everyday or something like that.
2. With extended response questions like this, unless they ask you for a net ionic equation, you only need to include a balanced chemical equation. Of course, it is up to you whether you would want to delete spectator ions or not! For me, I usually wouldnt unless the spectator ions really causes confusion.
3. No definitely not! Know at least 3 evidences, because questions like "assess the evidence for nitrogen oxides/sulfur oxides" are extremely common in exams. You would need around 3-4 evidences and account for those evidences and what they suggest about what we should do in the future to produce less of those oxides. Some evidences are NOAA flask and gas chromatograph measurements, increase in coal burning power plants and photochemical smog. There! You already have 3 more evidences besides acid rain!
4. Personally I do, but it doesnt make such a big impact upon your final mark for the response if you dont include a concluding statement. You've gotta present both sides (i.e. positive and negative) of the question and then have one short last sentence that expresses your opinion (e.g. the benefits of _______ outweighs the disadvantages of ________ and hence _________ definitely benefits the society more).
Ok so I've had a look at your response now, and I will just point out some of the good stuff and some of those not-so-good stuff that you can improve on. But look, overall I reckon this would be a response somewhere between
band 5 - band 6, and your teacher might choose to give you a high band 5. You have
fluently illustrated what the question asks you to do and demonstrated a
good understanding of those evidences and their impacts. You have in your establishing sentences
accounted for the occurrence of your acidic rain and stated briefly the reason for concentrations of these oxides in atmosphere (to be brief with these things is good because they dont directly answer the question but you are providing examiners with backgrounds). I must also applaud you on your
assessment of the evidences which is the question! Many candidates would forget or include very little judgments in their responses. What I often tell people to do is in the end just explicitly state the word judgment and state what your judgment is (i.e. "Judgment: __________________________"). It sounds a bit clumsy but it tells the teacher you are answering the assess part of the question!
Ok now lets move onto the defects of your response. The biggest defect in your response is that your evidences are limited. You have mentioned two evidences: gas measurement and a
whole tonne of info on acidic rain. This imbalance between the amount of explanation you put on gas measurement and the amount of explanation you put on acidic rain makes the examiner feel like "okay so this girl really knows her acidic rain stuff but she's just stating this gas measurement for the sake of stating it". I would recommend to either
take out some information about acid rains and put more information into gas measurement. Or you can just simply add more information in gas measurement. To make your response stronger, you should really
include another evidence such as photochemical smog.
Another defect is about your monitoring part of the question. You have used cause and effect language to explain the need for monitoring these acidic oxides but like what I said before, you are
focusing a little too much on the evidence part and you are not balancing out your monitoring part. You can
add one more point about the necessity to monitor these oxides (for example Nitrogen oxide's greenhouse effect is 100 times stronger than carbon dioxides) and you can also relate photochemical smog to your statement of acidic oxides being respiratory irritants.
Ok so out of 8 I would give a 6-7/8, and your teacher would most likely give you a mark like that as well (definitely not anything below 6). Overall its a very good piece of writing, well done!
Best Regards
Happy Physics Land