Names of Ions vs Elements (Sec 3)

This is another area that seems to be causing confusion to at least half of the students. The good news is that it is only half the students who don't get it.

This is what I saw in the test.

CaCO3 - Calcium Carbonate :)

Elements present in the compound: Calcium, Carbonate :( !!!

Obviously, there are some misconceptions here. Carbonate is the name given for a group of elements which form the CO3^2- ion. However, the elements that made up that ion are carbon and oxygen.

(Note: I used ^ as a sign that it is superscript for the charge as there is none in this blog, but bear in mind ^ is not part of chemical formulas of ions)

Likewise, in naming compounds, we have the halogens (F, Cl, Br, I) which are named as fluorine, chlorine, bromine and iodine respectively.

However, when they are written as part of a compound, their -ine would change to -ide.

e.g. NaCl is named as sodium chloride and not as sodium chlorine, but the element that is present in that compound is chlorine and not chloride.

Shockingly, such a simple knowledge is lacking even in the sec 4s who wrote that I^- as iodine instead of iodide ion.

Conclusion?

Naming of coumpounds:

CaSO4 - calcium sulphate
CaCO3 - calcium carbonate
KNO3 - potassium nitrate
KOH - potassium hydroxide
NaF - sodium fluoride
NaCl - sodium chloride
NaBr - sodium bromide
NaI - sodium iodide

Elements present in compounds:

CaSO4 - calcium, sulphur, oxygen
CaCO3 - calcium, carbon, oxygen
KNO3 - potassium, nitrogen, oxygen
KOH - potassium, hydrogen, oxygen
NaF - sodium, fluorine
NaCl - sodium, chlorine
NaBr - sodium, bromine
NaI - sodium, iodine

Test for carbon dioxide (Sec 3)

Okay, now this question came out in the 3B class test and it was kinda disappointing cos it was done in lab and who would have thought that hands on activity would not leave an impression with the students. For those who did not know, naturally left it blank, however, some had a vague impression and this was the answer.

"...add limewater to the solution, and it will turn chalky...."

2 mistakes... Firstly, we are testing for gas, so what does the word "solution" mean? The word "solution" means mixture in liquid state ... so it is kind of a contradicting as adding limewater in a liquid is not going to test for any gas.

I guess that is why most chemistry student do badly as they just write everything vaguely. Secondary 3/4 Science is not like Primary school science. More precise words need to be used.

Secondly, the word "chalky" is outdated. It will be marked as wrong. White solids are seen and in this case the solid has a name, called "precipitate" and I must mention someone spelt it as "perticipate" -_-"

Conclusion?

Test for carbon dioxide:

Bubble gas through calcium hydroxide (limewater) and white precipitate is formed.

To all students, pls read!!!!

Disclaimer:

This blog is to clear misconceptions of students in Chemistry and help them in the way they chose their use of words to answer.

It is not a blog whereby:

1. students come in hope that whatever is discussed here would come out in the class test/common test/exams/O levels.

2. students come in here for a quick summary of the various chapters in which they did not revise earlier for any test/exam.

It is only used as an aid to help students and students should not be too dependant on it. After every month, I'll post a summary of what is discussed so that it would be easier to refer to when the previous posts are archived.

This is for all levels that take Chemistry. Study this as a subject, not by topics. Feel it and you will realize that everything is interlink, if you treat it as a subject whereby you need to memorise without understanding much, you will have difficulty. Application is heavily tested now, especially in the new syllabus of Chemistry.

Keep loving Chemistry!!! :p

(A Big THANK YOU to former Maths and current Chemistry student of mine, Xinying, for helping me set this up as I haven't meddled with blog since NUS days... Also, I'm NOT linking my personal blog with this so forget about using this to read my other blog (not the livejournal one which I don't intend to update) which no one knows yet...hehe..)