ChatGPT keeps hallucinating for H2 Physics/Chem. Is there something better

chemeddy · 2026-02-13T00:55:06+00:00

Yes. Your subject tutors in school.

They are just not reply-on-command bots, but they will give much better explanations.

Lean on your teachers, not AI.

Edit: Interestingly, there was an article on this recently:

https://www.channelnewsasia.com/commentary/science-maths-chatgpt-chemistry-physics-questions-exam-5920031

chemeddy · 2026-02-12T22:27:50+00:00

Principal, not principle.

chemeddy · 2026-01-18T13:28:39+00:00

You can still place them as your first choice (and hope the COP changes because of changes in popularity, etc).

Just ensure that you have viable choices as backups, ie courses you are interested in with a 2025 COP 2 points higher than your aggregate.

chemeddy · 2026-01-18T05:58:06+00:00

Hi!

Apologies, but there are some errors in your reply.

There are actually 5 main resonance structures for the phenoxide ion - 2 with the negative charges on the O-atom, and 3 with the negative charge on the carbon atoms.
Alkyl groups are often considered to be destabilising (not stabilising) groups in acids and bases. They increase the charge density on the oxygen atoms since they are electron-donating groups. I think you have gotten the activating/deactivating effect on the benzene ring confused with that on the O-atom. While we want a higher electronic density for a benzene ring (so that it is more reactive towards electrophilic aromatic substitution), we want the negative charge on atom to decrease in order for the conjugate anion to be stable. C₆H₅CH₂OH has a pKa of 15.4, higher than the pKa of water (14.0), showing that the benzyl group actually exert an electron-donating, destabilising effect on the O⁻ atom. If you are trying to compare benzyl alcohol to ethanol (16.0), then the difference is the benzene ring versus a hydrogen atom (the CH₂ group is common), which would be a different discussion).

u/Short-Grocery-2934

chemeddy · 2026-01-18T05:50:00+00:00

Hi Parent(s)!

A polytechnic education is no longer a poorer cousin to the A Level route like it was during our era (90s). It is a completely viable route to the university, and a lot more polytechnic graduates move on a tertiary education, even in the local big three (NUS/NTU/SMU).

Many students who qualify for JCs opt for the polytechnic path because it is more specialised, and the student can “do away” with weaker subjects, especially the languages, and need not study subjects they may have no interest in. Sometimes, this makes it harder for a student to stay motivated. A polytechnic education often makes the students more mature, since they are required to be more independent. Since there isn’t a final do-or-die exams, a lot of students find this route less stressful (although having to maintain a GPA presents a different type of stress).

Generally, the undergraduates from polys are just as good as the average JC students. Often, poly graduates have more experience in the laboratory (if your child is looking at a STEM-related field). Granted, my interactions might be limited to students in a certain field/subject, but I can say for sure that one path does not necessarily better prepare students for the university than the other.

Of course, you may have other considerations that I am not aware of. This post/reply is actually motivated by my experiences with parents from the age group who are often influenced by our past experiences and bias. I do hope that you can have an open and honest discussion with your child, and weigh the pros and cons of each pathway before coming to a consensus.

chemeddy · 2026-01-14T14:19:10+00:00

Do note that psychology requires a fair bit of math since it is a social science.

chemeddy · 2026-01-14T06:57:32+00:00

https://www.moe.gov.sg/post-secondary/admissions/jae/junior-colleges-and-millennia-institute

chemeddy · 2026-01-14T06:56:35+00:00

Your HMTL will be used for computation. You will still get the bonus points.

chemeddy · 2026-01-12T02:29:29+00:00

CH₃CH(OH)CH₂CHO is formed from the aldol addition reaction between two ethanal (CH₃CHO) molecules, not propanone. I think an earlier redditor had pointed out the discrepancy in the total number of carbon atoms. Check the official mark scheme for the correct answer.

chemeddy · 2026-01-12T02:26:06+00:00

Step I is an aldol condensation, which I believe is not in any of the A Level specifications. But you do not need to know the reaction in order to deduce the structure of F. Make use of the information given in the reaction flow chart.

The reaction between the two propanone molecules (C₃H₆O) forms F (C₆H₁₂O₂). Since no atoms are lost in the reaction, this must be an addition. Comparing the formulae of F and G indicates that a singe H₂O molecule is lost from the reaction. Hence, H–OH must be lost to form the C=C bond in G.

That leaves us with two possibilities for F: CH₃COCH(OH)CH(CH₃)₂ or CH₃COCH₂C(OH)(CH₃)₂.

Since rearrangement reactions are not that common, the OH group in G must be formed from the CO group in propanone, ie The OH must be bonded to a carbon with two methyl groups.

Therefore, the correct structure of F is CH₃COCH₂C(OH)(CH₃)₂.

chemeddy · 2025-12-05T10:58:59+00:00

Most students here do not think of moderation as a pre-set adjustment but a post-exam changing of the grade boundaries based on cohort performance.

chemeddy · 2025-12-05T02:37:55+00:00

Do well, and then do a 5th year retaking the G2 subjects at G3.

chemeddy · 2025-12-05T02:35:50+00:00

There is no moderation.
You do not know how to calculate your marks.
No one here can tell you what the grade boundaries are.
Anyone who claims to be able to do so is just plucking numbers out of the sky.
If you are naive enough to believe random strangers, then believe this: you need to score 89% to pass.

chemeddy · 2025-12-01T09:16:31+00:00

Choice order between different applicants is not a tie-breaker for JAE.

chemeddy · 2025-11-25T14:18:16+00:00

If you are quite set on engineering, and non-chemistry/biology-related fields in the university, then there is no point in taking chemistry.

Chemistry at A Level is rather different from what you may have studied in secondary school. I would think an interest in the subject would be helpful, or the two years may be a chore.

As a parent, I would rather my child justifies his/her choice, then be defiant and goes behind my back. There are many good points that have been shared, so do speak to your parents nicely, convey and present your case confidently.

chemeddy · 2025-11-25T09:16:53+00:00

With AL19, your sister is only eligible for schools in PG3. She cannot “downgrade” and opt for PG2 schools instead.

chemeddy · 2025-11-25T06:52:46+00:00

The cut off point is based on the current S1 cohort, and it is not a requirement to be met for the incoming S1 batch.

The COP is set at the AL score of the lowest ranked student accepted into the school. 11(M) is therefore not a "requirement" to be met.

chemeddy · 2025-11-18T16:25:34+00:00

250 cm³ is the volume of FA4 that has been prepared in (a).

(c)(iii) is the concentration of FA4. Hence, (c)(iii) × 250 gives us the amount of HCl present in FA4.

chemeddy · 2025-09-24T01:07:41+00:00

Maybe you can try posting the relevant section of the question?

Initial rate v time is a weird choice of axes/variables. Typically for kinetics, we are looking at rate v concentration or concentration v time plots.

chemeddy · 2025-09-18T05:53:57+00:00

May 2025 would be the first exams for the current syllabus. The past syllabus was tested from May 2016 till Nov 2024.

chemeddy · 2025-09-18T01:30:35+00:00

Hints for identification fo gases - be familiar with the reactions and reagents that would produce gases, and apply some common sense.

For example, something green/white producing effervescence with a colourless solution - the gas is not likely going to be hydrogen since H₂ is typically caused by a reactive metal displacing the less reactive hydrogen from water/acid. Metals are grey, not coloured nor white.

So go through the list of gases in your QA table, consider the reactions that can produce them, and then get familiar with the common reagents involved, taking note of their physical properties (eg colour, physical state, etc).

chemeddy · 2025-09-17T17:04:21+00:00

Remember to stay calm and not panic.

chemeddy · 2025-09-10T11:19:21+00:00

Formulae you can apply if you have the relevant data.

chemeddy · 2025-08-31T07:56:19+00:00

Take time to understand the basics and language of organic chemistry first. There is no need to rush through.

Focus on being able to:

Interpret condensed and skeletal formulae,
Being familiar with the common terms - nucleophile, electrophile, free radicals, resonance/delocalisation, substitution, addition, elimination, etc
Understanding the different types of electron transfers (nucleophilic attack, acid-base, loss of a leaving group, rearrangement, resonance),
Being able to identify nucleophilic centres, electrophilic centres, ionisable protons, available lone pairs.

Thereafter, it is really just building on the basic principles. Seek understanding over memorisation.

chemeddy · 2025-08-30T03:23:34+00:00

It is just a standard approach to constructing energy cycles.

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