Hi.

As far as ‘‘O’’ level is concerned, there are 3 standard reactions for acids i.e. 1) acid + metal, 2) acid + base and 3) acid + metal carbonate. Meanwhile, there are 2 standard reactions for bases i.e. 1) base + acid (same as that for acid) and 2) base + ammonium salt. Therefore, we have the so-called 4 standard reactions since the acid-base neutralization repeats itself in both categories. Of course, there are cases when a given reaction doesn’t come under any of these 4 categories. Then, we just have to adopt the displacement reaction i.e. exchanging partners, such as the example which you had given. Sodium is a more reactive metal than iron(II), therefore it will displace iron(II) from its sulfate. If you cannot categorize a given reaction under any of these 4 categories, it is ‘‘safe’’ to adopt the displacement reaction, as far as ‘‘O’’ level is concerned. Actually, there is one more reaction too i.e. metal + water to give salt and hydrogen.

Chemistry Teacher

Sure, no problem.


Cheers,
Chemistry Teacher

Hi. Firstly, we have to be clear on one thing: Are you talking about valence electrons or the total number of electrons? For instance, if A has 3 electrons in total, then A has to be from Group 1 ( Remember your electronic configuration-2,1) If A has 3 valence electrons then, A has to be from Group 3.


In this question, there is no ambiguity because there is no way an element has 12 valence electrons (octet rule), although elements in Period 3 can expand their octet configuration. Therefore, it is safe to declare that W has 12 electrons in total. If that is the case, then W has to be from Group 2 i.e. magnesium (electronic configuration-2,8,2). Logically, Y has to be hydrogen.

The result is an ionic compound which is magnesium hydride. In this special scenario, the hydrogen takes on a -1 charge i.e. H-. H+ is more common, but in the presence of a highly electropositive element such as magnesium, H takes on a -1 charge. Therefore, you have to draw the dot and cross diagram for magnesium hydride (ionic compound) i.e. MgH2 or WY2

Chemistry Teacher

Hi all,


I am opening this thread to assist students who have difficulties in their ‘‘O’’ level and ‘‘A’’ level chemistry.
I will try my best to answer your questions.

Cheers,
Chemistry teacher

Personally, I feel that we should not stress the students unnecessarily. Let me state a few reasons for my '‘optimism’. Most of our kids started their preparation rather late. In fact, I feel that one should already start to prepare for PSLE since primary 4. Yes, primary 4, no kidding. The students need to have a solid foundation before they proceed to more difficult concepts. Nope, this is not an act of "kiasu-ness". In my view, it is better for the students to learn the difficult concepts slowly (2 years to learn), rather than letting them cram everything into their tiny brains at the last minute (in their final P6 year).

Even if the students do badly for their PSLE, it is not the end of the world. Touch wood! Should they end up in the normal stream, they will still have a chance to fight back at the end of year 2 (streaming). If they do well for the streaming, they will be converted back to the express stream. I know it is easier said than done. That is why we should show care and concern for our kids. We need to be patient with them. Nevertheless, we should not forget that some students are late-boomers. As long as they get themselves promoted to secondary schools, then we should thank our lucky stars already

Hi.

Nope, it is not necessarily to use model drawings to solve all the maths problems. For instance, if the number involved is fairly large, it will be difficult and tedious for the student to draw so many units of boxes. In fact, the use of model drawings is only one of the few techniques that the child has to know. Other techniques include:
1. Use Before & After
2. Look for Patterns
3. Work Backwards
4. Use Guess & Check etc.
Personally, I have always preferred the use of ratios over modelling. As for speed-related questions, it is advisable for the student to "draw out’’ the question, since a picture speaks a thousand words.

Chess will be a good board game to start with. If you are interested in chess coaching, do drop me an email at [email protected].