As you can see from the on-going survey on the right hand side, Mole Calculations (commonly known as Mole Concepts) has been voted by students as the #1 Killer Topic in O Level Chemistry (and other equivalent basic Chemistry Syllabus).
In fact, a large number of students skip the calculation-based questions when they see it on Chemistry examination, fearing that they spend alot of time on that question, and yet could not answer it.
Over the years, this topic is often voted the “Hot Favorite” on students’ challenging topics. Some:
- have problems understanding what the question is asking for
- do not know where to start
- totally blank when they read the question
- too confused with the formulae to use
- gave up on Mole Calculations totally
Many a times, question will require you to write a Balance Chemical Equation in order to solve the question. Other times, they will also require you to write the Ionic Equation and state the Spectator Ion.
As such you will need the following basic foundations that i have shared some time ago:
4 Steps-Process to write a Balanced Chemical Equation
7 Steps-Strategy to write the Ionic Equation & Spectator Ion
The best way to learn is NOT TO READ, but to DO IT!
Let’s try out one exam-based question(similar to O Level Chemistry Exams):
Question 1:
Copper (II) oxide reacts with dilute sulfuric acid to produce a salt, copper (II) sulfate and water. This process is known as Neutralisation.
i) Write a balanced chemical equation with state symbols
ii) Write the ionic equation and state the spectator ion of this reaction
PS: Try it out and leave your answers below.
a)CuO+H2SO4–>CuSO4+H20(already balanced)
b)Cu(2+)+O(2-)+2H(1+)+SO4(2-)–>
Cu(2+)+SO4(2-)+H20
Therefore,the ionic equation is:
2H(1+) + O(2-)–>H20
The spectator ions are:
Cu(2+) and SO4(2-)
Sean,i hope these are the correct answers but i have a little confusion about souluable and insoluable bases.can u tell which are soluable and insoluable cuz i cant find them anywhere.
Thanx!
Reply
sean Reply:
May 6th, 2010 at 12:30 am
Hi Varda,
You chemical equation is balanced, and thus correct,
However, your Ionic Equation is not correct.
CuO is an insoluble base and thus it will have the state symbol (S).
Which also means you can’t split CuO. Try it out again.
Regards,
Sean Chua
Reply
Varda Reply:
October 12th, 2010 at 11:25 pm
so the ionic equation will be:
CuO+2H(1+)->Cu(2+)+H2O
is it correct?
Reply
Please reply!!!my exams are near…..i really need help on which are soluable and which are insoluable bases!!!!
Reply
sean Reply:
May 6th, 2010 at 12:34 am
Most metal oxides are insoluble in water. (General)
Several common oxides are known to dissolve in water such as:
Sodium Oxide
Potassium Oxide
all other group I Metal Oxide
Barium Oxide
The above are the common ones.
Reply
Can any one tell me if this is correct?
Umm, varda, if what i’m saying is correct might answer your question.
Soluble salts:
-All sodium
-All potassium
-All ammonium
-All nitrates
-All chloride except Lead (ii) Chloride,Silver chloride.
-All sulphates except Barium , Calcium, Lead (ii).
Insoluble salts
All carbonate except sodium carbonate, potassium carbonate, ammonium carbonate.
Reply
sean Reply:
May 6th, 2010 at 12:31 am
Hi Carlyn,
This is correct for the Table of Solubility of Common Salts. Check out my archive blogpost on SALTS to find more discussions.
Regards,
Sean
Reply
Sean, is it correct?
And can you tell me how to solve a ionic equation?
And the topic on mole?
Reply
sean Reply:
May 6th, 2010 at 12:32 am
Use the SEARCH bar or “SEARCH BY TOPICS” on the RHS column to access past discussions on it.
All The Best! Enjoy!
Reply
balanced equation is
cuo(s)+H2SO4(aq)=cuso4(aq)+H2O(l)
thus ionic is
cuo+2H+=CU2++H2O
Reply
a) CuO (s)+ H2SO4(aq) = CuSo4(aq) + H2O(l)
b) Cu+2 + SO4_2 = CU + SO4
Reply