1. Balancing equation
Use visualizer is better

2. Chemical equation 2 No There are 3 H in the products
Word equation: potassium + water potassium hydroxide solution + hydrogen Chemical equation: K (s) + H2O (l)  KOH (aq) + H2(g)
reactants
products 2
How many H in the reactants?
Is it equal to the number of H in the products? No
There are 3 H in the products

3. What can we do? Balance it!
Chemical equation: K (s) + H2O (l)  KOH (aq) + H2(g)
2 H(Hydrogen) in reactants
3 H (Hydrogen)
in the products
We can’t change to H3O

4. What can we do? Balance it! 2
Chemical equation: K (s) + H2O (l)  KOH (aq) + H2(g) 2
2 H(Hydrogen) in reactants
3 H (Hydrogen)
in the products
We can’t change to KOH2, but
we can multiple KOH by 2

5. What can we do? Balance it! 2
Chemical equation: K (s) + H2O (l)  KOH (aq) + H2(g) 2
2 H(Hydrogen) in reactants
4 H (Hydrogen)
in the products

6. What can we do? Balance it! 2 2
Chemical equation: K (s) + H2O (l)  KOH (aq) + H2(g) 2 2
2 H(Hydrogen) in reactants
4 H (Hydrogen)
in the products
multiple by 2 in the beginning

7. What can we do? Balance it! 2 2 However…….. K ….
Chemical equation: K (s) + H2O (l)  KOH (aq) + H2(g) 2 2
4 H(Hydrogen) in reactants
4 H (Hydrogen)
in the products
YEAH~~~Hydrogen is now balanced~~
Oxygen is now balanced~~~
However…….. K ….

8. What can we do? Balance it! 2 2 2
Chemical equation: K (s) + H2O (l)  KOH (aq) + H2(g) 2 2 2
Don’t worry~
Write 2 in front of K, it will be balanced~

9. What can we do? Balance it!
Chemical equation: 2 K (s) + 2 H2O (l)  2 KOH (aq) + H2(g)

10. Challenge Exercise: Hydrogen + oxygen  water
Write the chemical equation with the correct states of matter
2H2(g) O2(g)  2H2O (l)

13. Common ions
Cations Li+ Na+ K+ Group I Mg2+ Ca2+ Group II Al3+ Group III Common metals: Ag+ Cu+ Cu2+ Fe2+ Zn2+ Pb2+

14. Anions F- Cl- Br- I- Group VII O2- Group VI Polyatomic Ion: OH- (hydroxide) NO3- (nitrate) CO32- (carbonate) SO42- (sulphate)