1. Atoms must be conserved!
Balancing equations
Atoms must be conserved!

2. Balancing equations What you learn in this section:
How to balance simple equations.
Tests for anions (negative ions)
Chlorides Cl-
Sulfates SO42- and Sulfites SO32-
Carbonates CO32- and hydrogencarbonates HCO3-
Nitrates NO3-
Phosphates PO43-

3. Balancing equations
The law of conservation of mass states the total mass of the products in chemical reaction = to the total mass of the reactants.
Law of Conservation of Matter states in any chemical reaction matter is neither created or destroyed but is changed from one form to another.

4. Balancing equations Counting Atoms
How many atoms of each element are in the following molecules?
1. H2SO4
2. Ca(OH)2
3. NaCl
4. (NH3)3P04
5. 3H2O
6. 4Al2(CO3)3
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5. Balancing equations Answers
1. 2 hydrogen, 1 sulfur, 4 oxygen
2. 1 calcium, 2 oxygen, 2 hydrogen
3. 1 sodium, 1 chlorine
4. 3 nitrogen, 9 hydrogen, 1 phosphorus, 4 oxygen
5. 6 hydrogen, 3 oxygen
6. 8 aluminum, 12 carbon, 36 oxygen

6. Balancing equations
A chemical equation is a way of representing a chemical change.
It shows reactants and products.
To balance an equation means to change the numbers of each molecule involved, so that the same number of atoms of each element appear on the reactants side and on the products side.
Chemical equations balance on an atomic level, not molecular.

7. Balancing equations
You cannot change the formula of a substance, i.e. if the equation has NH3 you cannot change this you can only put a number in front of it, 2NH3, increasing the number of N’s and the number of H’s.
Never change the subscripts (small numbers).
It is possible to write balanced equations for lots of reactions but that does not mean that the reaction actually takes place.

8. Balancing equations Is this equation balanced?
NaCl + H2O  NaOH + Cl2
left side has 1Na, 1Cl, 2H, and 1O
right side has 1Na, 1O, 1H, and 2Cl
NO!!!!!! It is not balanced!!
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9. Balancing equations Yes!!!!!! It is balanced!! HCl + NaOH NaCl+ H2O
left side has 2H, 1Cl, 1Na, and 1O
right side has 1Na, 1Cl, 2H, and 1O
Yes!!!!!! It is balanced!!
5/17/2018

10. Balancing equations Is this equation balanced?
Ca + H2O Ca(OH)2 + H2
left side has 1Ca, 2H, 1O
right side has 1Ca, 2O, 4H
No!!!!!! It is not balanced!!
How can we make it balance????
5/17/2018

11. Balancing equations Ca + H2O  Ca(OH)2 + H2
We need more H’s, but we can’t add just the H atom, we have to add the entire molecule the H is attached to:
Putting a 2 in front of the H2O gives
1 Ca + 2 H2O  1 Ca(OH) H2

12. Balancing equations 1 Ca + 2 H2O  1 Ca(OH)2 + 1 H2
Just like in math, this equation may be written in a simpler way:
Ca + 2 H2O Ca(OH)2 + H2
(be sure you write the “2” on your worksheet!)

13. Balancing equations What is balanced in a chemical equation?
Three things are balanced in a chemical equation:
1. Atoms
2. Mass
3. Charge

14. For now, you will only be concerned with balancing atoms
For now, you will only be concerned with balancing atoms. Remember, the number of atoms of each element on the reactants side must equal the number of atoms of each element on the products side!
When we do redox equations we will need to balance the electrons too.

15. Balancing equations Balance the following

16. Balancing equations Balance the following
NaPO3 + CuO -> NaCuPO4
SO3 + H2O -> H2SO4
Be(OH)2 -> BeO + H2O
BaO + H2O -> Ba(OH)2
Na2SO3 + S -> Na2S2O3
SO2 + H2O -> H2SO3
Li2O + H2O -> LiOH
Na2HPO4 -> Na4P2O7 + H2O
H4As2O7 -> As2O5 + H2O
CaC2 + N2 -> CaCN2 + C
HAsO3 -> As2O5 + H2O

17. Tests for Anions Anion test observation inference Chloride
Add a few drops of AgNO3 to a soln. of the solid
White ppt formed that is soluble in ammonia soln.
Ag+ + Cl-  AgCl
Sulfate or
Sulfite
1. add BaCl2 soln. to a soln. of the solid
2.add dil HCl
1. white ppt formed.
2. ppt disolves = sulfite, or
ppt remains = sulfate.
Ba2+ + SO42-  BaSO4 or
Ba2+ + SO32-  BaSO3
BaSO4 + HCl no reaction or
BaSO3 +2HClBaCl2 +SO2 +H2O

18. Tests for Anions Anion test observation inference Nitrate
To a soln of the solid add freshly made FeSO4 soln then add conc H2SO4 BROWN RING TEST
A brown ring is formed at the junction between the two liquids.
Brown ring due to presence of the nitrate ion.
phosphate
Ammonium molybdate added to a soln of the solid. Conc. HNO3 added and the soln warmed
Yellow ppt is formed.
Phosphate ions are present.

19. Tests for Anions Anion test observation inference Carbonate CO32-
Hydrogen-carbonate
HCO3-
1. add dilute HCl to the solid.
Fizzing, gas given off that turns limewater milky
CO32-+2H+CO2+H2O
HCO3-+H+CO2+H2O
Limewater
Ca(OH)2+CO2 CaCO3+H2O
2. add MgSO4 to a fresh soln of the solid.
White ppt  carbonate
no. ppt.  hydrogencarbonate. Boiling gives a ppt.
Mg2++CO32-MgCO3
Mg2++HCO3- Mg(HCO3)2
Boiling
Mg(HCO3)2MgCO3+ CO2+H2O