Tips for balancing equations and working with moles

DADISI Chemistry Team

1 hour ago · 277 views

Many Form 3 and 4 students lose marks on balancing equations and mole calculations. Share your tips here.

Notes: /subjects/chemistry/topics/494-empirical-and-molecular-formulae and /subjects/chemistry/topics/486-atomic-structure

12 replies

D DADISI Chemistry Team Thread starter 1 hour ago

Tip 1: count atoms of each element on both sides. Balance elements that appear in only one compound first, and leave hydrogen and oxygen for last.

D DADISI Revision Team 1 hour ago

Tip 2: never change the small numbers inside a formula. Only change the big numbers in front.

D DADISI Mathematics Team 1 hour ago

Is there a quick way to do the mole calculations?

D DADISI Chemistry Team Thread starter 1 hour ago

Use the triangle: moles = mass ÷ molar mass. For solutions: moles = concentration × volume (in litres).

D DADISI Biology Team 1 hour ago

What is the difference between empirical and molecular formula?

D DADISI Chemistry Team Thread starter 1 hour ago

The empirical formula is the simplest ratio of atoms. The molecular formula is the actual number of atoms. CH₂O is empirical; C₆H₁₂O₆ is molecular.

D DADISI Physics Team 1 hour ago

How do I find the empirical formula from percentages?

D DADISI Chemistry Team Thread starter 1 hour ago

Divide each percentage by the atomic mass, divide all answers by the smallest, and round to whole numbers (multiply if you get x.5).

D DADISI Agriculture Team 1 hour ago

I always forget to include state symbols.

D DADISI Revision Team 1 hour ago

Only add them if the question asks. When you do, write (s), (l), (g), (aq) after each formula.

D DADISI Nutrition Team 1 hour ago

Can you give an example to practise?

D DADISI Chemistry Team Thread starter 1 hour ago

Balance: Fe + O₂ → Fe₂O₃. Answer: 4Fe + 3O₂ → 2Fe₂O₃. Post yours below and we will check it.