Semester 2 Review. THE MOLE Using the mole and molar mass, make conversions between moles, mass and number of particles. Use molar mass to calculate percent.

Semester 2 Review

THE MOLE

Using the mole and molar mass, make conversions between moles, mass and number of particles.

Use molar mass to calculate percent composition, empirical formula, and molecular formula.

How many moles are equivalent to 2.58x1024 atoms of gold?

Answer: 4.29 mol

What is the molar mass of ammonium phosphate? (NH4)2SO4

Answer: 132.16 g/mol

A chemical used in batteries is 63.0% Manganese and 37.0% Oxygen. What is the empirical formula?

Answer: MnO2

The empirical formula of a compound is P2O5. The molar mass of the compound is 284 g/mol. What is the molecular formula?

Answer: P4H10

Calculate the percent composition of copper (I) sulfide (Cu2S).

Answer: 79.85% Cu and 20.15% S

STOICHIOMETRY

Convert from one substance to anotherDetermine amount of reactant/productDetermine limiting reactant/excessDetermine theoretical & percent yieldUse density to convert between

substances

Using the following balanced chemical reaction:

CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

How many molecules of oxygen are needed to react with 2.45 mol of CH4?

2.95 x 1024 molecules O2

What volume of hydrogen gas is produced if there are 112 g NH3 in the following reaction at 1.15 atm and 23

degrees Celsius? 2NH3(g) N2(g) + 3H2(g)

208 L

If reactant “A” runs out before reactant “B” and the reaction stops, then reactant “A” is known as the …

LIMITING REACTANT

Using the following reaction,

2Na(s) + 2H2O(g) 2NaOH(aq) + H2(g)

If you have 15.2 g of Na and 12.5 g of H2O, how many grams of H2 gas can be made?

0.658 g H2

If the theoretical yield of a reaction is 125 g and the actual yield is 115 g, what is the percent yield?

92.0 %

GASES

STP valuesUse gas laws to determine pressure,

volume, and temperature.Use gas laws to determine moles or grams

or molar mass.Use gas laws and stoich. to determine

amounts of reactants and products.

What are STANDARD conditions for gases?

0oC or 273 K and 1 atm or 101.3 kPa pressure

A sample of gas has a volume of 25 mL and a temperature of 65oC. What will the volume be if the temperature is raised to 125oC?

29 mL

How many grams of gas are present in a sample that has a molar mass of 70.0 g/mol and occupies 2.00 L at 117 kPa and 35.1oC?

6.36 g

What is the pressure in atmospheres of a 0.108 mol sample of helium gas at a temperature of 20.0oC if its volume is 0.505 L?

5.14 atm

Calculate the mass of solid ammonium nitrate that must be used to obtain 0.100 L of dinitrogen monoxide gas at STP.

NH4NO3(s) N2O(g) + 2H2O(g)

0.357 g

SOLUTIONS

Solubility (“like dissolves like”)Concentration (molarity)Vocab

unsaturated, saturated, supersaturated, soluble, insoluble, miscible, immiscible

Electrolytes and Non-Electrolytes

What is the molarity of a 500. mL solution that contains 125 g of sodium hydroxide?

6.25 M

How many milliliters of a 0.850 M solution of sodium thiosulfate, Na2S2O3, contain 0.350 mol of Na2S2O3?

0.412 L

Identify which of the following substances are soluble in water:

CaF2 Al

C3H8

CCl4

CaF2

For which type of substance does an increase in pressure increase solubility?

gases

A ____________ solution contains the maximum amount of solute it can hold. An __________ solution contains less than the maximum amount. A ____________ solution contains more than the maximum amount.

saturated, unsaturated, supersaturated

RATES

Collision Theory Factors that Affect RateHow and Why Rate Changes Over TimeCatalysts

Reactants must collide (with enough energy and the correct orientation) in order to produce an activated complex and form product.

Describe collision theory.

How does a catalyst increase the rate of a reaction?

It lowers the activation energy by creating an alternate path.

How does the rate of a reaction change over time?

The rate slows down because the concentration of the reactants decreases over time.

EQUILIBRIUM

Completion vs. ReversibleRates of Reactions at EquilibriumKeqLeChatelier’s PrincipleEquilibrium ExpressionsCalculating KKsp

A ________ reaction is represented by , while a ______ reaction is represented by .

completion, reversible

2 NO2 (g) N2O4 (g) + Energy

What happens if we… Lower the Temperature

Increase N2O4

Decrease NO2

Increase PressureIncrease Volume

Shift rightShift leftShift leftShift rightShift left

What does it mean if the reaction shifts to the right? How would the amounts of reactants and products change?

The reactions favors the forward reaction so the amounts of reactants decrease and products increase.

Equilibrium Expressions

Write the equilibrium constant for the following reaction:

N2 (g) + 3 H2(g) 2 NH3(g)

Keq = Keq = [NH[NH33]]22 [N[N22][H][H22]]33

Calculate Keq for the reaction below if [S2] = 0.0540 M, [H2] = 0.0377 M, and [H2S] =

0.184 M.2 H2S (g) 2 H2(g) + S2(g)

Keq = 2.27 x 10-3

What does a large value for Keq mean? A small value for Keq?

Large means products are favored at equilibrium while small means reactants are favored

Which of the substances below is most soluble? Least soluble?CaF2 – 3.5 x 10-11

PbCrO4 – 2.3 x 10-13

Al(OH)3 – 4.6 x 10-33

MgCO3 – 6.8 x 10-6

Most soluble = MgCO3

Least soluble = Al(OH)3

ACIDS & BASES

Electrolytes and Strong vs. WeakBronsted – LowryAmphoprotic – AmphotericpH calculationsTitrations

What is the pH of 0.00025M HCl (a strong acid)?

Answer: 3.60

What is the concentration of H+ if the pOH is 7.82?

6.61 x 10-7M

What word is used to describe substances that can act as an acid or a base?

Answer: Amphoteric

Strong acids and bases ionize ___________ while weak acids and bases ionize __________.

completely, partially

Label the A, B, CA, CB in the following reaction:

HSO4- (aq) + H2O (l) H3O+ (aq) + SO4

2-

HSO4- (aq) + H2O (l) H3O+ (aq) + SO4

2-

A B CA CB

A student titrates 40.0 mL of an H2SO4 solution of unknown concentration with 24.64 mL of a 0.550 M NaOH solution. What is the molarity of the H2SO4 solution?

H2SO4 + 2 NaOH 2 H2O + Na2SO4

[HCl] = 0.169 M