1. Unit 13: Stoichiometry -How can we quantitatively analyze reactions?
-What limits the yield of a reaction? Why should we care?
-How can a chemical equation best represent a reaction?
-What are the patterns we can use to accurately predict products?

2. State Symbols
In a chemical equation, we want to communicate as much information about our reaction as possible.
We often use a set of symbols to note what state of matter the __________ and the ____________ are in.
Consider the following reaction from our lab:
reactants
products

3. 2 Mg + O2  2 MgO State Symbols
In what state of matter were each of the products and reactants?
Reactants
Magnesium _________
Oxygen___________
Products
Magnesium oxide __________
solid
gas
solid

4. State Symbols Mg + 2 HCl  MgCl2 + H2
To indicate each of the states of matter, we use a subscripted letter or two after each substance in the reaction.
(s) – solid
(g) – gas
(l) – liquid
(aq) – aqueous solution

5. State Symbols Mg + 2 HCl  MgCl2 + H2
Incorporating them in to our equation makes it look like this:
Mg HCl  MgCl2 + H2
As you can see, the subcripted state symbols are written in the same position as the numerical subscripts for a compound
But how do we know what states of matter to expect from our products or reactants outside of the lab?
(aq)
(g)
(s)
(aq)

6. States of Matter for Elements and Compounds
In their elemental form, we know that most elements are solids at room temperature.
What elements are exceptions to this?
Liquids – _______________________
Gases – ________________________________ ________
For compounds, we will usually have them in one of two forms: solid or aqueous solution
How do we know if a substance is soluble or not?
Bromine and mercury
Hydrogen, nitrogen, oxygen, fluorine, chlorine

7. Solubility Chart
A very useful reference chart known as a solubility chart can tell you whether or not a substance is soluble in water.
If it is soluble, we would use the______ symbol.
If it is not, we would use the _____ to indicate that it had precipitated out of the solution.
The following page shows a common solubility chart.
(aq)
(s)

8. S = soluble I = insoluble SS = slightly soluble X = other Bromide Br-
Bromide Br-
Carbonate CO3-2
Chloride Cl-
Hydroxide OH-
Nitrate NO3-
Oxide O-2
Phosphate PO4-3
Sulfate SO4-2
Aluminum Al+3 S X I
Ammonium NH4+
Calcium Ca+2 SS
Copper (II) Cu+2
Iron (II) Fe+2
Iron (III) Fe+3
Magnesium Mg+2
Potassium K+
Silver Ag+
Sodium Na+
Zinc Zn+2
S = soluble
I = insoluble
SS = slightly soluble
X = other

9. Solubility Chart
To determine whether or not a substance is soluble, you look at its cation and anion and see where they cross in the chart.
Determine if the following are soluble:
Sodium nitrate – ______________
Magnesium oxide – ______________
Copper (II) chloride – ______________
Copper (II) hydroxide – ______________
Zinc sulfate – ______________
soluble
insoluble
soluble
insoluble
soluble

10. Solubility Chart What would the chemical equation look like?
What would happen if we put potassium chloride solution into a test tube with sodium nitrate?
What would the chemical equation look like?
KCl + NaNO3  KNO3 + NaCl
With the state symbols, how would it appear?
KCl(aq) + NaNO3(aq)  KNO3(aq) + NaCl(aq)
All of our reactants and products are soluble, so what would we see? - NOTHING!
We would say that there was “no visible reaction” which we abbreviate as NVR

11. Solubility Chart
Write the chemical equation for the reaction of magnesium sulfate and potassium phosphate.
Predict the products
MgSO4 + K3PO4  Mg3(PO4)2 + K2SO4
Balance the chemical equation
3MgSO4 + 2K3PO4  Mg3(PO4)2 + 3K2SO4
Write in the state symbols using the solubility charts
3MgSO4(aq) + 2K3PO4(aq)  Mg3(PO4)2 (s) + 3K2SO4(aq)

12. Activity Series
Single replacement reactions are different when it comes to predicting whether or not a reaction will occur.
A metal will replace another metal in an ionic compound if the metal element is more “active” than the metal in the compound
How do we know which metal is more active?
Look at an Activity Series!

13. Lithium Potassium Calcium Sodium Magnesium Aluminum Manganese Zinc
Metal Activity Series for Single Replacement Reactions
Metal
Metal Ion
Reactivity
Lithium
Potassium
Calcium
Sodium
Magnesium
Aluminum
Manganese
Zinc
Chromium
Iron
Lead
Copper
Mercury
Silver
Platinum
Gold
Li+ K+
Ca2+
Na+
Mg2+
Al3+
Mn2+
Zn2+
Cr2+, Cr3+
Fe2+, Fe3+
Pb2+
Cu2+
Hg2+
Ag+
Pt2+
Au+, Au3+
Most Reactive -
Least Reactive

14. Activity Series
The higher the metal is on the chart, the more active it is.
It can replace any metal underneath it in an ionic compound when in solution
Example: Al + CuCl2  Cu + AlCl3
This reaction was what you carried out at the end of the Chemical Changes lab, when the aluminum wire was placed into the solution of copper (II) chloride

15. Activity Series
Determine whether the following reactions will occur or not, based on the activity series:
Zinc and lead (II) nitrate _________
Calcium and copper (II) chloride __________
Iron and sodium hydroxide _________
Aluminum and zinc bromide _________
Aluminum and calcium carbonate ________
Aluminum and silver sulfide ________
Yes
Yes No
Yes No
Yes

16. Activity Series
The reaction occurs between the metal cations in solution gaining electrons from the metal atoms as they turn from atoms into ions
Have the cations been reduced or oxidized?
________________________
How do you know?
________________________________________ ________________________________________
Reduced
Gain electron – reduction , lose electron – oxidation

17. Quantitative Use of Equations
Possible interpretations:
Molecular ratios of reactants and products
Mole ratios of reactants and products
Mass ratios of reactants and products

19. Stoichiometry
The study of the amount of reactants needed and products generated in a _________ _________.
There are _________ steps needed to solve a Stoichiometry problem.
If your initial units are __________ and your final units are moles, skip steps ___ and ___.
You only need the mole-mole ratio from the coefficients of the chemical reaction.
chemical
reaction
five
moles 2 4

20. Stoichiometry Write a complete and _____________ chemical equation.
Convert quantity of given into __________.
Multiply by the mole _____ taken from the ________________ in the chemical equation.
Convert from moles into the desired unit.
_____________ units to ensure that correct conversion factors were used.
balanced
moles
ratio
coefficients
Cancel out

21. Stoichiometry
What volume of ammonia is produced if 25.0g of nitrogen (diatomic molecule) is reacted with excess hydrogen?
Write a complete and _____________ chemical equation.
_______________________________________
Convert mass of nitrogen into moles by dividing by the molar mass.
balanced
N2 + 3H2  2NH3
x 1mol N2
28 g N2
25.0 g N2

22. Stoichiometry Multiply by the mole ratio.
________________________________________
Convert moles into the desired units
Cancel units.
Answer: _______________
x 1mol N2
28 g N2
x 2 mol NH3
1 mol N2
25.0 g N2
x 1mol N2
28 g N2
x 2 mol NH3
1 mol N2
x 17.0 g NH3
1 mol NH3
25.0 g N2
x 1mol N2
28 g N2
x 2 mol NH3
1 mol N2
x 17.0 g NH3
1 mol NH3
25.0 g N2
30.4 g NH3

23. Limiting Reagents
A limiting reagent is a reactant that is in less molar quantity or the reactant that determines the quantity of _________________.
product produced

24. For example, if we react 2.5 grams of sodium with 300,000 grams of chlorine, we wouldn’t get 300,002.5 grams of sodium chloride
We would run out of sodium atoms before we ran out of chlorine atoms
Therefore, the sodium “limits” the amount of sodium chloride that can be produced and is our limiting reagent

25. Limiting Reagents
Problem: How many grams of NH3 can be produced from the reaction of 20 g of N2 and 6 g of H2?
Calculate the moles of each reactant.
_______________________________________
20 g N2
x 1 mol N2
28 g N2
= mol N2
x 1 mol H2
2 g H2
6 g H2
= 3 mol H2

26. Limiting Reagents According to the equation, N2 + 3H2  2NH3
Problem: How many grams of NH3 can be produced from the reaction of 20 g of N2 and 6 g of H2?
According to the equation, N2 + 3H2  2NH3
For every 1 mole of nitrogen, I would need ________ moles of hydrogen.
However, I have been given moles of N2 and 3 moles of H2. To use all the N2, I need 3 x = 2.14 moles of H2.
There would be __________________ moles H2 remaining.
Therefore, nitrogen is the ___________ reagent and hydrogen is the __________ reagent.
three
3 – 2.14 = 0.86
limiting
excess

27. Limiting Reagents
This means my Stoichiometry must be based on the quantity of nitrogen since I will need all of it producing the Ammonium.
_______________________________________
0.86 mol H2 x 2 g H2/1 mol H2 = 1.72 g H2 remains
How much hydrogen was used?
Answer: ______________________
x 1mol N2
28 g N2
x 2 mol NH3
1 mol N2
X 17.0 g NH3
1 mol NH3
20.0 g N2
= g NH3
6 g H2 – 1.72 g H2 = 4.28 g H2

28. -How can we quantitatively analyze reactions?
-What limits the yield of a reaction? Why should we care?
-How can a chemical equation best represent a reaction?
-What are the patterns we can use to accurately predict products?