O level question - Blast Furnace

Metanoia SG

Hi all, would like to check on an MCQ from 2013.

Which gases that go into the bottom of the blast furnace undergo a reaction during the extraction of iron?

1. Carbon dioxide 2. Nitrogen 3. Oxygen

A. 1 only B. 1, 2 and 3 C. 1 and 3 only D. 3 only

Would you include nitrogen (forming nitrogen oxides) as your answer?

Zzzfrendzzz SG

Nope

jurongresident SG

~~deleted~~

Metanoia SG

Well, according to a guide book,
- hot air is blown into the furnace near the bottom.
- Carbon burns in oxygen to form carbon dioxide.
- Carbon dioxide reacts with more coke (Carbon) to form carbon monoxide.
- Carbon monoxide reduces iron(III) oxide in haematite to iron.

:. Carbon Dioxide

Yup, that would be within the context of the blast furnace.

Thinking beyond this chapter, wouldn't students be required to be aware (from the chapter of Air) that nitrogen oxides are formed in high temperature enviroments?

jurongresident SG

I am sorry, but I think the correct answer should be that both carbon dioxide and oxygen react in the blast furnace.

Let me explain. (You may want to Google for images and videos of furnace, to see how a blast furnace looks like)

Say we have an iron ore (haematite) and we want to extract iron from it.

Haematite contains iron(III) oxide and impurities, such as sand and clay (limestone).

To extract the iron, we add the haematite, limestone and coke (carbon) from the top of the blast furnace.

Next, we blow hot air into the furnace near the bottom.

The oxygen in the hot air reacts with coke (carbon) to form carbon dioxide.

The carbon dioxide in the hot air, as well as the carbon dioxide formed, reacts with more coke (carbon) to form carbon monoxide.

This carbon monoxide reacts with iron(III) oxide to form iron and carbon dioxide.

The carbon dioxide formed (and not used at all) escapes through the top of the furnace, along with carbon monoxide (either did not react or not used at all) and nitrogen, as waste gases.

The iron is formed in molten state and it runs to the bottom of the furnace.

As mentioned earlier, the haematite contains impurities such as sand and clay (limestone). When iron is formed in molten state, it is mixed with the impurities.

The heat decomposes the limestone (calcium carbonate) into quicklime (calcium oxide) and carbon dioxide.

This quicklime (calcium oxide) then reacts with acidic impurities such as silicon(IV) oxide (sand) to form a liquid called slag.

This slag floats on top of the molten iron and they run off separately at the bottom of the furnace. Slag can be sold for use as a constituent of cement.

With that, we obtain the molten iron.

jurongresident SG

Air is a mixture of several gases.

The percentage composition (by volume) of clean air is as follows,

Nitrogen: 79%
Oxygen: 20%
Carbon Dioxide: 0.03%
Water vapour: 0-5%
Noble gases: Argon: 0.9%
Noble gases: Neon and Helium: 0.002%

Oxides of Nitrogen (nitrogen monoxide and nitrogen dioxide) are formed from the following sources, when the temperature is very high:
- lightning activity during thunderstorms
- internal combustion engines

jurongresident SG

I confess that the contents I write here are written word-for-word from a guidebook titled “Perfect Guide ‘O’ Level Science (Chemistry)”. I know this is plagiarism, but I feel that to avoid saying the wrong stuff, it’s better that I write word-for-word. If this violates rules and regulations, the moderators may remove the plagiarised content.

UltimaOnline SG

Hi all, would like to check on an MCQ from 2013.

Which gases that go into the bottom of the blast furnace undergo a reaction during the extraction of iron?

1. Carbon dioxide 2. Nitrogen 3. Oxygen

A. 1 only B. 1, 2 and 3 C. 1 and 3 only D. 3 only

Would you include nitrogen (forming nitrogen oxides) as your answer?

Both of you (Metanoia and jurongresident) are O level Chemistry tutors, yes?

Again, it's Cambridge's fault for setting ambiguous qns like these (every year there'll be a couple of such qns, in which different school teachers will disagree with each other and/or with Cambridge, and teach their students different answers) at both O levels and (especially) A levels.

The most correct answer (regardless of whether it's the answer Cambridge wanted, which is always debatable for such qns), is that all 3 gases do indeed react at the high temperatures present in blast furnances (whether for extraction of iron from its ore, or other purposes).

As nitrogen (the most abundant gas in the atmosphere) is inevitably present in the air used by blast furnaces (air is afterall, the cheapest source of oxygen, and obviously all industries are profit-oriented and want to make as much money as possible by reducing costs), at such high temperatures of blast furnaces, it's inevitable that various oxides of nitrogen (NOx) are generated. Such oxides of nitrogen are toxic to humans, and are known to be a industrial medical health hazard for blast furnace workers.

While the O level syllabus doesn't specifically include mention of this health hazard suffered by blast furnace workers, nonetheless (assuming you believe Cambridge wants you to including nitrogen as the correct answer) at O levels and A levels, students are arguably expected to put 2 and 2 together (presence of nitrogen and oxygen, and at high temperatures) and conclude oxides of nitrogen may (and are) being produced in blast furnaces, albeit as undesirable (and medically hazardous) side-products.

lixuansim SG

Yes

Metanoia SG

Yup, I'm a tutor and I raised this question to check the consensus; its one of those that could be argued either way.

Appreciated Jurongresident's detailed reply, apologies if he spent the extra time to do it thinking I'm a student.

For what it's worth, the publishers (cambridge?) suggested answer is only carbon dioxide and oxygen, but I thought a student shouldn't be faulted to include nitrogen also.

Accounts of the need for NOX control in blast furnace has been documented, within the secondary textbook; we might also link it to the chapter on Air and Air pollution.

Alas, its one of those ambiguous questions for tutors and students to take note.

UltimaOnline SG

Yup, I'm a tutor and I raised this question to check the consensus; its one of those that could be argued either way.

Appreciated Jurongresident's detailed reply, apologies if he spent the extra time to do it thinking I'm a student.

For what it's worth, the publishers (cambridge?) suggested answer is only carbon dioxide and oxygen, but I thought a student shouldn't be faulted to include nitrogen also.

Accounts of the need for NOX control in blast furnace has been documented, within the secondary textbook; we might also link it to the chapter on Air and Air pollution.

Alas, its one of those ambiguous questions for tutors and students to take note.

TYS publishers are not certainly not Cambridge. TYS publishers pay MOE for the right to publish the questions (the answers are by the various authors hired by the publishers), as the copyrights are co-owned by Cambridge and MOE. The official Cambridge mark schemes are (by law, due to a legal agreement between MOE and Cambridge) confidential and cannot be revealed to the public. It is fairly common (especially for A levels, when it becomes even more complicated) for all the different TYS publications available on the market to all give different answers for an ambiguous, challenging or problematic, open-ended Singapore A level exam question (every year there's a couple of such qns). This happens even for MCQs, but naturally to a lesser extent.

Metanoia SG

Yup, I understand the publishers are not Cambridge, I was just wondering if they have any access to the marking scheme.

Its unfortunate that the marking schemes and markers reports for the CIE exams are so freely avalible online while the Singapore-Cambridge versions are shrouded in mystery.

jurongresident SG

Yup, I understand the publishers are not Cambridge, I was just wondering if they have any access to the marking scheme.

Its unfortunate that the marking schemes and markers reports for the CIE exams are so freely avalible online while the Singapore-Cambridge versions are shrouded in mystery.

From what I heard, if I heard correctly, the people who create the "answer key" for TYS open-ended questions are JC students or University students, who are hired by the publisher to write the answer for them.

eagle SG

TYS answer keys are not written by JC students. They are qualified educators usually I guess.

I was approached by one publisher for the O Level Physics before, but I was hesitant because of the numerous conceptual errors that the TYS answers contain for previous years and do not really want my name to be on the answer key. Fortunately they managed to find another person to author the answers.

Different TYS will have different mistakes. The main problem is that students may not be able to understand that the answers are conceptually wrong because they may regard TYS answers as the holy grail.

OrdinaryStudent123 SG

The correct answer based on Cambridge Examiner's Report is A, CO2 ONLY.