1. Reminder
If you are opting out of lab, please Mr. Chris Scott ASAP!
11/23/2018

2. 3.70)
When baking soda (NaHCO3) is heated, it releases carbon dioxide gas, which is responsible for the rising of cookies, donuts, and bread. (a) Write a balanced equation for the decomposition of the compound (one of the products is Na2CO3). (b) Calculate the mass of NaHCO3 required to produce 20.5 g of CO2.
2NaHCO3 CO Na2CO H2O Δ
CO2 is ~44 g/mol and NaHCO3 is about 84 g/mol.
78.3 g NaHCO3
11/23/2018

3. Do You Understand Limiting Reagents?
In one process, 124 g of Al are reacted with 601 g of Fe2O3.
Which reactant is the limiting reagent?
2Al + Fe2O Al2O3 + 2Fe
g Al
mol Al
mol Fe2O3 needed
g Fe2O3 needed OR
g Fe2O3
mol Fe2O3
mol Al needed
g Al needed
1 mol Al
27 g Al x
1 mol Fe2O3
2 mol Al x
160 g Fe2O3
1 mol Fe2O3 x =
124 g Al
367 g Fe2O3
Start with 124 g Al
need 367 g Fe2O3
Have more Fe2O3 (601 g) so Al is limiting reagent
11/23/2018

4. Calculate the mass of Al2O3 that should be possible
to obtain with the amounts of reactants used. .
g Al
mol Al
mol Al2O3
g Al2O3
2Al + Fe2O Al2O3 + 2Fe
1 mol Al
27 g Al x
1 mol Al2O3
2 mol Al x
102 g Al2O3
1 mol Al2O3 x =
124 g Al
234 g Al2O3
Limiting reagent determines the amount
of product possible! This amount is called
the theoretical yield.
11/23/2018

5. Theoretical Yield is the amount of product that
would result if all the limiting reagent reacted.
Actual Yield is the amount of product actually
obtained from a reaction.
% Yield =
Actual Yield
Theoretical Yield
x 100
11/23/2018

6. A sample problem Calculate the % yield for the formation of Al2O3
assuming that you obtained 100 g.
% Yield =
Actual Yield
Theoretical Yield
x 100
% Yield =
100 g
234 g
x 100
= 42.7 %
11/23/2018

7. Remember Actual yield is the amount of product
obtained when the reaction is carried out
in the lab
(2) Theoretical yield is the amount of product
calculated from the balanced equation based on
a given amount of limiting reagent
(3) A measure of how well your reaction worked
% Yield =
Actual Yield
Theoretical Yield
x 100
11/23/2018

8. 8.86) Consider the reaction MnO2 + 4HCl MnCl2 + Cl2 + 2H2O
If 0.86 mole of MnO2 and 48.2 g of HCl react, which reagent will be used up first? How many grams of Cl2 will be produced? Calculate the % yield for an experiment that produced 10.0 g of Cl2.
125 g HCl needed, only have 48.2 g HCl…
so HCl must be the limiting reagent
considering 48.2 g HCl, 23.4 g Cl2 should be
produced
10.0g/23.4g x 100% = 42.7% yield
11/23/2018

9. Sample problem
3.73)
Each copper (II) sulfate unit is associated with 5 water molecules in crystalline copper (II) sulfate pentahydrate (CuSO4.5H2O). When this compound is heated in air above 100oC, it loses the water molecules and also its blue color. If 9.60 g of CuSO4 are left after heating g of the blue compound, calculate the number of moles of water originally present in the compound.
0.300 mol
11/23/2018

10. Reactions in Aqueous Solution
Chapter 4

11. A solution is a homogenous mixture of 2 or more substances
The solute is the substance present in the smaller amount
The solvent is the substance present in the larger amount
Solution
Solvent
Solute
Solder- usually a Pb-Sn alloy used to fuse metals.
Soft drink (l)
H2O
Sugar, CO2
Air (g) N2
O2, Ar, CH4
Soft Solder (s) Pb Sn
11/23/2018

12. An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity.
A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity.
nonelectrolyte
weak electrolyte
strong electrolyte
11/23/2018

13. Conduct electricity in solution?
Cations (+) and Anions (-)
Strong Electrolyte – 100% dissociation
NaCl (s) Na+ (aq) + Cl- (aq)
H2O
Weak Electrolyte – not completely dissociated
CH3COOH CH3COO- (aq) + H+ (aq)
11/23/2018

14. Hydration is the process in which an ion is surrounded by water molecules arranged in a specific manner.
-helps to stabilize ions in solution and prevents cation from combining
with anions δ+ δ-
H2O
11/23/2018

15. Ionization of acetic acid
CH3COOH CH3COO- (aq) + H+ (aq)
A reversible reaction. The reaction can occur in both directions.
Acetic acid is a weak electrolyte because its ionization in water is incomplete.
11/23/2018

16. Nonelectrolyte does not conduct electricity?
No cations (+) and anions (-) in solution
C6H12O6 (s) C6H12O6 (aq)
H2O
11/23/2018

17. Can we electrocute a pickle?
11/23/2018

18. Pickles are full of electrolytes…
11/23/2018

19. 3 types of reactions in aqueous medium
Precipitation
Acid-base
Oxidation-reduction
11/23/2018