2. Balancing Chemical Equations Molecular masses of compounds (review) Balancing simple equations Practice makes perfect!

3. Chemical Equations Al 2 (SO 4 ) 3 + H 2 O → Al(OH) 3 ↓ + H 2 (SO 4 ) – Is this equation “balanced” – “Conservation of Mass” principle – The number of moles on the left hand side of the equation has to equal the number of moles on the right hand side – Aluminum- 2 moles on left and 1 mole on right…the equation is NOT balanced. – Same for Oxygen, Hydrogen, Sulfur

4. So…how do we balance it? “a” Al 2 (SO 4 ) 3 + “b” H 2 O → “c” Al(OH) 3 ↓ + “d” H 2 (SO 4 ) – Start with the most complex product and work to the more simple – With the molecules you cannot change the formula! – Keep sacred the “Conservation of Mass” principle – Aluminum- 2 moles on left and 1 mole on. Try “2” for “c”…now aluminum balanced left and right.

5. Balancing equations…continued “1” Al 2 (SO 4 ) 3 + “b” H 2 O → “2” Al(OH) 3 ↓ + “d” H 2 (SO 4 ) – Substitute 1 for a and 2 for c. – Now look at the sulfate group (SO 4 )…there are three on the left (reactants) and one on the right. – Try 3 for d…now the sulfates balance. “1” Al 2 (SO 4 ) 3 + “b” H 2 O → “2” Al(OH) 3 ↓ + “3” H 2 (SO 4 ) Now count oxygens (not the one’s in the sulfate group…you already accounted for them)…6 on the left, so try subbing 6 for b. (next slide…)

6. Balancing equations…continued 2 “1” Al 2 (SO 4 ) 3 + “6” H 2 O → “2” Al(OH) 3 ↓ + “3” H 2 (SO 4 ) 2 Al, 3(SO 4 ), 12H, and 6O: 2Al, 6O, 6H, 6H, 3(SO 4 ) It’s balanced!!! Check page 161 of text…it’s wrong in the text! Assignments in text and trial quiz on website. This is great math and logic practice!