O Levels Chemistry Question: Metals & Reactivity Series

06 Oct

Posted by: sean in: Chemistry Notes & Tips

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Halo Students,

Chemistry Practical is round the corner and Chemistry Paper 2 in less than 3 week time.
Hope your preparation is going well.

Since this is the weekend, i think you might want some more conceptual chemistry questions to think it through. Here is the start of more to share:

Question:
Calcium Carbonate decomposes more readily on heating than sodium carbonate. Suggest a reason for this.

CaCO3 –> CaO + CO2
Na2CO3 –> Na2O + CO2

Think about it.

PS: Leave your suggested answers in the “Comments” section below.

Rgds
Sean

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12 Responses

zhengning
07|Oct|2007 1

I would like to give this a try, not sure of the correct answer however.

Hmmm is it because Na is a more reactive metal as compared to Ca? The more stable the compound, the higher the temperature is needed for decomposition. Hence, Na2CO3 will takes a longer time…

I think? hahaha.

Reply
lijun(:
07|Oct|2007 2

actually, i do somewhat understand this, but i can never get it penned down in words. =/

all i know is that,
since sodium is more reactive than calcium, it will form a more stable carbonate than calcium. hence, sodium carbonate will not decompose as easily as calcium carbonate.

can u please explain this in greater detail? thanks.

Reply
Anonymous
07|Oct|2007 3

Sodium is higher than calcium in the reactivity series, thus making it more reactive and forming more stable compounds. Thus calcium carbonate decomposes more readily than sodium carbonate.

I hope I’m right. :\

Reply
Sean Chua
09|Oct|2007 4

Halo Zhengning, Lijun and Anonymous.

Well Done. In fact all three of you got the concepts spot-on and i thought your answers are GOOD.

“Na is more reactive than Ca, and thus forms a much stable compound with Carbonate. It is like Na is so reactive that they “hold” carbonate so tightly and strongly that they requie higher heat energy to break the ionic bondig”-informal annswer for understanding.

Rgds,
Sean
SimpleChemConcepts
“Learning Experience with A Difference”

Reply
FluffySnow
16|Oct|2007 5

hmm. IMO, shouldn’t Calcium carbonate be more stable than sodium carbonate?

Calcium carbonate is infact Ca2(CO3)2, which means that the electrostatic forces between the calcium and carbonate ion should be stronger as compared to Sodium carbonate, which only has 2 sodium ions forming bonds with a single carbonate ion.

So, shouldn’t calcium carbonate, with 2 calcium ions attached to 2 carbonate ions, be more stable?

Reply
sean Reply:
January 17th, 2009 at 6:27 pm
Hello FluffySnow,

Do note that the correct chemical formula for calcium carbonate is CaCO3, which are formed by the Cation Ca2+ and Anion CO32-.

Back to the question on the stability of the carbonates from decomposition due to heating.

You need to understand the Metals & Its Reactivity Series.

Na metal is more reactive than Ca metal. As such, Na would love to react more readily with any substance, as compared to Ca.

The compound that is formed by Na will be more stable now..ie, the electrostatic attraction btw the Na+ & CO32- in the compound is much stronger.

The compound that is formed by Ca will be less stable (as compared to Na compound), i.e. the eletrostatic attraction btw the Ca2+ & CO32- in the compound is less strong.

As such, CaCO3 is more easily to decompose by heat, as compared to Na2CO3.

Hope this explanation helps.

Cheers
Sean =)

As such,

Reply
Okpewho Princess
21|Jul|2009 6

why is chlorine used in water treatment

Reply
sean Reply:
October 15th, 2009 at 1:41 pm
Hi Okpewho,

Chlorine water is used as an disinfectant for municipal water for developed and developing countries. Chlorine can be applied for the deactivation of most microorganisms and it is relatively cheap.

Hope this information helps.

To Your Academic Success in Chemistry,
Sean Chua =)

Reply
waleed bin qasim
09|Oct|2009 7

K
Na higher in reactivity series. very reactive but also forms a very stable compound. like a stronger magnet forms a stronger attraction.
Ca. hence below in the reactivity series less reactive as compared.and forms less stable or strong bond as compared.
Mg
.
.
C

sir do comment. waiting.

Reply
sean Reply:
October 15th, 2009 at 1:37 pm
Hi Waleed Bin Qasim,

Yes. Your thought on this question is spot on. Very good analogy using magnet also.

Keep up your good work.

To Your Academic Success in Chemistry,
Sean Chua

Reply
Saud
27|Feb|2010 8

observing the reactivity series of the metals…………….Ca is below Na …………..this depicts that calcium is relatively less reactive than sodium. this means that calcium “less” prefers to be in forms of ions than sodium. this is said as sodium carbonate is more to heat than Calcium carbonate therefore CaCO3 decomposes better than Na2CO3.

Reply
sean Reply:
May 6th, 2010 at 1:02 am
cool.

Reply