Brainlag PlusTurning measured masses into moles to find the numbers in a balanced equation, the simplest formula of a compound, and its molecular formula.
Masses to an equation
If you know the mass of every substance in a reaction, you can find the balancing numbers without guessing.
- 4.8 g Mg reacts with 3.2 g O₂ to make 8.0 g MgO (Mg = 24, O = 16)
- moles: Mg 4.8 ÷ 24 = 0.20, O₂ 3.2 ÷ 32 = 0.10, MgO 8.0 ÷ 40 = 0.20
- divide by the smallest (0.10): 2 : 1 : 2
- 2Mg + O₂ → 2MgO
If dividing by the smallest leaves a half (1 : 1.5), multiply everything by 2.
The rest of this lesson and its 9 practice questions are in Plus.
Screen 1 of 4, free to read.
- 9 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards