Chemistry 11: Video Solutions for Mathematical based Problems.
Instructions: Use the following video’s for further clarification.
Unit 5
S. 5.2 – The Mole
Calculations Relating the Number of Moles and The Mass of Substance.
Ex. 1: What is the mass of 5.21mol NH3 (soln)
Ex. 2: What is the mass of 1.46·102 NaBr? (soln)
Ex. 4: Determine the number of moles of C2H5OH there are in 355 g C2H5OH. (soln)
Finding molar mass from amount of substance and mole of substance.
Ex. If 0.140 mol of acetylene gas has a mass of 3.64 g, what is the molar mass of acetylene?
(soln)
Calculations relating the number of moles and the volume of gas.
Ex. 1: What is the volume occupied by 2.30 mol of O2(g) at STP? (soln)
Ex. 2: How many moles of any gas is contained in a 25 L sealed container at STP? (soln)
Converting moles to particles.
Ex. 1: How many particles are there in 0.252 mol CO. (soln)
Ex. 2: How many moles of NO3 are there in 9.88·1020 particles of NO3. (soln)
S. 5.3 – Multiple Conversions Between Moles, Mass, Volume and Number of Particles.
Ex. 1: What is the mass of 2.35·1025 particles of NaCl. (soln)
Ex. 2: How many particles of C3H8(g) (propane) at STP are contained in a 200 L tank. (soln)
Ex.3: What is the volume at STP of 63.56 g CH4 gas? (soln)
Liquid and solid volumes involving the mole.
Ex. 1: What is the volume occupied by 6.00 mol methane CH4(l)? (d = 0.466g/mL) (soln)
Ex. 2: How many moles of C3H8O (propanol) are contained in 350 mL (d = 0.800 g/mL)
(soln)
Ex. 3: What is the density of Cl2(g) at STP? (soln)
Ex. 4: A 4.00 L jug of milk contains 34.56 g of gas at STP. What is the molar mass of the
gas? (soln)
Ex. 5: C3H8O (propanol) has a density of C3H8O = 0.800 g/mL. How many atoms of C are
in 250 mL of C3H8O? (soln)
S. 5.4 Percentage Composition.
Ex. 1: What is the percentage composition of H2O. (soln)
Ex. 2: What is the percent composition of C3H8O.(soln)
Ex. 3: What is the percentage of phosphate in the compound V3(PO4)5· 4H2O. (soln)
S. 5.5 – Empirical and Molecular Formulae.
Empirical Formula
Ex. 1: What is the empirical formula of a compound consisting of 15.9 % B, 84.1 % F.
Assume 100.0 g of the compound is taken. (soln)
Ex. 2: What is the empirical formula of a compound consisting of21.8 % Mg, 27.9 % P,
50.3 % O. Assume 100.0g of the compound is taken. (soln)
Molecular Formula
Ex. 1: A molecule has an empirical formula of CH2 and a molar mass of 54.06 g. What is
the molecular formula? (soln)
Ex. 2: A gas has the empirical formula POF3. If0.350 L of the gas at STP has a mass of 1.62
g, what is the molecular formula of the compound? (soln)
Ex. 3: The empirical formula of a compound is SiH3. If 0.0275 mol of a compound has a
mass of 1.71 g, what is the compound's molecular formula? (soln)
S. 5.6 - Molar Concentration
Molarity.
Ex. 1: Find [NH4Cl] if you have 50.0 mL of 0.0700 mol NH4Cl. (soln)
Ex. 2: What is the molarity of 45.56 g NaCl(s) being dissolved in 3 L of water. (soln)
Ex. 3: How many moles of CH4 are in 3.5 L solution of 2.23 M CH4. (soln)
Ex. 4: The molarity of CS2 is 16.6M. What is the density of CS2. (soln)
Simple Dilution Calculations.
Ex. 1: If 50 mL of 12 M HCl was added to 450 mL water, what is the final[HCl]. ([ ] =
concentration). (soln)
Ex. 2: How much 12.0 M HCl is required to make up a 1.00 L solution of 2.00 MHCl. (soln)
Mixing two solutions having different concentrations.
Ex. 1: If 500 mL 2.00 M HCl was added to 300 mL 1.00 M HCl, what is theresulting [HCl].
(soln)
Unit 7
S. 7.1 - The Meaning of the Coefficients in a Reaction Equation.
Ex. 2: C3H8(g) + 5 O2(g)→ 3 CO2(g) + 4 H2O(l)
a) How many molecules of C3H8are required to react with 10 molecules of O2? (Soln)
b) How many moles of CO2 areproduced when 2 mole of C3H8 are reacted? (Soln)
S. 7.2 - Stoichiometry Calculations Involving Moles, Mass, Gas Volume and Molecules.
Ex. 1: Convert moles of A into moles of B for the equation of: A + B → C (Soln)
Ex. 2: Nitromethane, a fuel occasionally used insome drag racers, burns according to the
reaction: 4 CH3NO2(l)+ 3 O2(g) → 4 CO2(g)+ 6 H2O(l) + 2 N2(g)
a) What mass of H2O is produced when0.150 g of CH3NO2(g) is burned? (Soln)
b) What combined volume of gas at STP isproduced if 0.316 g of CH3NO2 is burned?
(Soln)
c) What volume of O2(g) is requiredto produce 0.250 g of CO2? (Soln)
d) What mass of H2O is produced when0.410 g of CO2 is produced? (Soln)
S. 7.3 - Stoichiometry Calculations Involving Molar Concentration.
Ex. 1: What volume of 0.556 M HCl has enough hydrochloric acid to combine exactly with
25.4 mL of aqueous hydroxide with a concentration of 0.458 M? The equation for the
reaction is: HCl(aq) +NaOH(aq) → NaCl(aq)+ H2O (Soln)
Ex. 2: A student prepared a solution of HCL that was approximately 0.1 M andwished to
determine its precise concentration. A25.00 mL portion of the HCl solution was transferred
to a flask, and after a few drops of indicator were added, the HCl solution was titratedwith
0.0775 M NaOH solution. The titration requiredexactly 37.46 mL of the standard NaOH
solution. What was the exact molarity of the HClsolution. HCl(aq) + NaOH(aq) → NaCl(aq) +
H2O (Soln)
S. 7.4 - Stoichiometry of Excess Quantities.
Ex. 1: Use the following reaction to answer the proceeding questions.
2 Al + 3 Cl2 → Al2Cl6
a) What is the limiting reactant if 20.0 g of Al and 30.0 g of Cl2are used to produce
Al2Cl6.(Soln)
b) By how much is the excess reactant in excess. (Soln)
Ex. 2: Use the following reactionequation to answer the proceeding questions.
2Ca3(PO4)2+ 6 SiO2 + 10 C → P4+ 6 CaSiO3 + 10 CO
a) What mass of P4 is produced when 41.5 g of Ca3(PO4)2,26.5 g of SiO2 and 7.80 g of
C are reacted according to the equation: (Soln)
b) How many grams of each excess reactant will remain un-reacted? (Soln)
S. 7.5 – Percentage Yield and Percentage Purity.
Percent yield calculations
Scenario 1:
Ex: When 19.5 g of CH4 is reacted with an excess of Cl2according to the
reaction:
CH4 + Cl2→ CH3Cl + HCl
A total of 15.7g of CH3Cl is formed. What isthe percentage yield of the
reaction? (Soln)
Scenario 2.
Ex: What mass of K2CO3 is produced when 2.50 g of KO2is reacted with an
excess of CO2 according to the reaction.
4 KO2(s) +2 CO2(g) → 2 K2CO3(s)+ 3 O2(g)
If the reaction has a 23.0 % yield? (Soln)
Scenario 3.
Ex: What mass of CuO is required to make 15.0 g of Cu according to the
reaction:
2 NH3 + 3CuO → N2 + 3 Cu + 3 H2O
If the reaction has a 60.2 % yield? (Soln)
Unit 9
S. 9.6 – Calculating the Concentration of Ions in Solution.
Ex.1: What is the molar concentration of the chloride ions in 0.75 M AlCl3(aq)? (soln)
Ex. 2: What is the concentration of each type of ion in a solution made by mixing 200
mL of 0.355 M AlBr3 and 250 mL of 0.300 M CaBr2. (soln)