Detail in Answering Long Response Questions

[davemate03]

You can hide this advertisement by registering.

Hey guys, i was just wondering, for an 6 mark question in Shipwrecks, how much would you expect to write, hypothetically?

For example,
"One of the most common allows of iron is stainless steel. Outline how you could compare the rate of corrosion of i) Iron ii) Steel iii) Stainless steel"
6 MARKS

The success one answer says:
"Obtain identical samples of iron, steel and stainless steel.
Leave several samples of each in:
1) Air
2) Water
3) Acidic Solution
4) Salt Solution
5) Alkaline solution

Keep all other conditions (e.g. temperature and quantities) constant
Leave for several days then record any changes and hence evidence of corrosion. Repeat the experiment to confirm the result.

In my answer, I did the above, except
1) I only did a "salt solution" since it only asks for the rate of corrosion, not to test whether corrosion works in only air/water/alkaline solutions etc. Is this valid?
2) I quantitatively massed the samples before and after to determine any mass changes therefore, corrosion.

Am I going into too much detail? Or is the success one answer just too shallow? It doesn't seem like much to write for 6 marks.

[sam5]

Originally Posted by davemate03

Hey guys, i was just wondering, for an 6 mark question in Shipwrecks, how much would you expect to write, hypothetically?

For example,
"One of the most common allows of iron is stainless steel. Outline how you could compare the rate of corrosion of i) Iron ii) Steel iii) Stainless steel"
6 MARKS

The success one answer says:
"Obtain identical samples of iron, steel and stainless steel.
Leave several samples of each in:
1) Air
2) Water
3) Acidic Solution
4) Salt Solution
5) Alkaline solution

Keep all other conditions (e.g. temperature and quantities) constant
Leave for several days then record any changes and hence evidence of corrosion. Repeat the experiment to confirm the result.

In my answer, I did the above, except
1) I only did a "salt solution" since it only asks for the rate of corrosion, not to test whether corrosion works in only air/water/alkaline solutions etc. Is this valid?
2) I quantitatively massed the samples before and after to determine any mass changes therefore, corrosion.

Am I going into too much detail? Or is the success one answer just too shallow? It doesn't seem like much to write for 6 marks.

to further draw it out for the 6 marks, i would talk about reliability (repetition and validity (is the experiment testing what you want it to test?)

I would have done the experiment in a salt solution (NaCl is good...dont do ammonium chloride as the pH of this solution will impact on the results) and also in water (as a control, to see what it is like in a solution that isnt really an electrolyte).

A quantitative analysis isnt required unless stated. Its good to see that u r thinkin like that...but corrosion experiments tend to be more qualitative. Observation is generally a good enough measure of corrosion extents, but u can do quantitative if u want. remember that all original samples should be the same mass.

the question was too vague to be talking about pHof the solutions. The text should have specified for effects of pH if thats what it wanted.

Remember to always stay true to scientific method. Also remember that textbook questions arent as good as the real hsc questions.

[jellybelly59]

salt solution isn't enough to get you the mark... you have to know that to contribute to rusting you have to have air and water... so have one with just air inside, one with silicon oxide grains (to make it oxygen free), one with water filled half way and one with water all the up and finally one with salt water halfway and one all the way up. I have a 1 - 10 scale of rusting. 10 being super rusty and 1 being not so rusty lol.

As sam5 said... this experiment is qualitative>quantitative. Make sure you talk about reliability, validity and accuracy.. oh and talk about the chemistry behind the experiment placing chemical equations where appropriate.