Chemistry SOL Review— Molar Relationships The Mole and Mole Calculations The molar mass = the sum of all the atomic masses. Example Ca(NO 3 ) 2 = 40.08

Chemistry SOL Review— Molar Relationships

The Mole and Mole Calculations

The molar mass = the sum of all the atomic masses.

Example Ca(NO3)2 = 40.08 + 2(14.01) + 6(16.00) = 164.10 grams

You try one:

What is the gram formula mass (molar mass) of Mg3(PO4)2?

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You try one:What is the gram formula mass (molar mass) of Mg3(PO4)2?

3(24.305) + 2(30.97376) + 8(15.9994) = 262.86 grams






3(24.305) + 2(30.97376) + 8(15.9994) = 262.86 grams

What is the percent Magnesium in Mg3(PO4)2?

Answer: 3(24.305) x 100 = 27.7% 262.86

What is the percent Lithium in Li2SiO3?molar mass = 2(6.941) + 28.0855 + 3(15.9994) = 89.9657 g% Li = 2(6.941) x 100 = 15.4% 89.9657






3(24.305) + 2(30.97376) + 8(15.9994) = 262.86 grams

What is the percent Magnesium in Mg3(PO4)2?

Answer: 3(24.305) x 100 = 27.7% 262.86

What is the percent Lithium in Li2SiO3?


A Brief Return to Empirical Formulas

Empirical Formulas are the reduced form of Molecular formulas.

For example: The empirical formula for C5H10 is CH2.

A favorite SOL type question:

What is the empirical formula of a compound that contains 30% Nitrogen and 70% Oxygen?

a) N2Ob) NO2

c) N2O5

d) NO

This is really a percent composition problem. Figure out which compound contains 30% nitrogen.

Nitrogen gas is a diatomic molecule. What is Nitrogen gas is a diatomic molecule. What is the mass of one mole of nitrogen gas?the mass of one mole of nitrogen gas?AA 7 g7 gBB 14 g14 gCC 28 g 28 g DD 6 x 106 x 102323 g g

How many grams of nitrogen are present in How many grams of nitrogen are present in 2 moles of HNO3?2 moles of HNO3?A A 11B B 22C C 1414D D 28 28

What is the mass in grams of one mole of What is the mass in grams of one mole of sulfur dioxide (SO2)?sulfur dioxide (SO2)?A A 48.1 g48.1 gB B 64.1 g 64.1 g C C 80.1 g80.1 gD D 96.1 g96.1 g

What is the molar mass of Al(NO3)3?What is the molar mass of Al(NO3)3?A A 57 g/mol57 g/molB B 103 g/mol103 g/molC C 165 g/mol165 g/molD D 213 g/mol 213 g/mol

What is the percentage of aluminum in What is the percentage of aluminum in aluminum oxide (Al2O3)?aluminum oxide (Al2O3)?AA 47%47%BB 48%48%CC 53% 53% DD 54%54%

A compound is composed of 85.64% carbon A compound is composed of 85.64% carbon and 14.36% hydrogen. The compound has a and 14.36% hydrogen. The compound has a formula mass of 42.08 grams. What is the formula mass of 42.08 grams. What is the molecular formula?molecular formula?AA CH2CH2B B C3H6 C3H6 CC C2H4C2H4DD C2H18C2H18



At Standard Temperature and Pressure (STP) 1 mole of gas = 22.4 L

You can use this to calculate the density of a gas in g/Liter at STP.

Example: What is the density of CO2 gas at STP?

The molar mass of CO2 = 12.0111 + 2(15.9994) = 44.0099 g

Density = mass/volume = 44.0099 g/22.4 L = 1.96 g/L








What is the density of Cl2 gas at STP?








What is the density of Cl2 gas at STP?

Answer: molar mass = 2(35.453) = 70.906 g

70.906 g/22.4 L = 3.165 g/L

What is the density of carbon What is the density of carbon dioxide at STP?dioxide at STP?

AA 1.96 g/L 1.96 g/L

BB 22.0 g/L22.0 g/L

CC 46.0 g/L46.0 g/L

DD 5.09 x 105.09 x 10-1-1 g/L g/L



One mole = 6.02 x 1023 representative particles

One mole = 22.4 Liters of gas at 0°C and one atmosphere of pressure

One mole = the atomic mass listed on the periodic table.

For example: one mole of Helium contains 6.02 x 1023 atoms of Helium and it has a mass of 4.00260 grams. At 0°C and one atmosphere of pressure, it would occupy 22.4 Liters.

GivenGiven UnknownUnknown

1 1 XX KnownKnown

UnknownUnknown GivenGiven

How many liters would 2.0 moles of Neon occupy?

Sample problem: How many liters would 2.0 moles of Neon occupy?

Answer:2.0 moles Ne x 22.4 Liters Ne = 44.8 Liters Ne

1.0 moles Ne

Sample problem: How many moles are in 15.2 grams of Lithium?

Answer: 15.2 g Li x 1 mole Li = 2.19 mole Li

6.941 g Li






Sample problem: How many liters would 14 grams of Helium occupy?

Answer:14 g He x 22.4 L He = 78 Liters He 4.0026 g He






You try one:

What is the mass of 9.0 Liters of Argon gas at 0°C and one atmosphere of pressure?






What is the mass of 9.0 Liters of Argon gas at 0°C and one atmosphere of pressure?

9.0 L Ar x 39.948 g Ar = 16 g Ar 22.4 L Ar

Which volume will be occupied by a gas containing 6.02 Which volume will be occupied by a gas containing 6.02 x 10x 102323 atoms at STP? atoms at STP?AA 1.0 L1.0 LBB 11.2 L11.2 LCC 22.4 L 22.4 L DD 44.8 L44.8 L

Which of these is about 2 moles?Which of these is about 2 moles?AA 2.0 liters (dm3) of H22.0 liters (dm3) of H2BB 4.0 grams of H2 4.0 grams of H2 CC 2.0 x 102.0 x 102323 molecules of H2 molecules of H2DD 4.0 kilograms of H24.0 kilograms of H2

The gas with the largest volume at STP is —The gas with the largest volume at STP is —A A 10.0 g He 10.0 g He B B 10.0 g Ne10.0 g NeC C 10.0 g Ar10.0 g ArD D 10.0 g Kr10.0 g Kr

How many moles of copper are equivalent to 3.44 x 1023 How many moles of copper are equivalent to 3.44 x 1023 atoms of copper?atoms of copper?A A 0.571 moles 0.571 moles B B 1.75 moles1.75 molesC C 5.41 x 105.41 x 102121 moles molesDD 5.71 x 105.71 x 1022 22 molesmoles


Stoichiometry

For reaction calculations, the molar ratio is used.

Example:How many moles of nitrogen will react with 9 moles of hydrogen to produce ammonia according to this equation?

2N2(g) +3 H2(g) → 3NH3(g)

Given: 9 moles H2, Find moles N2

9 mol 9 mol HH22

xx 2 mol 2 mol NN22

= = 6 mol 6 mol NN22

3 mol 3 mol HH22

Mole ratio


Stoichiometry

For reaction calculations, the molar ratio is used.

Example 2:How many grams of nitrogen are needed to react with 2.0 grams of hydrogen using this equation?

2N2(g) +3 H2(g) → 3NH3(g)2 moles 3 moles 28.02 g 2.02 g

Given: 2.0 grams H2, Find grams N2

2.0 g H2.0 g H22 XX 2 X2 X 28.0228.02 = = 19 g N19 g N22

1 3 X 2.021 3 X 2.02

Formaldehyde (H2CO) reacts with oxygen to form CO2 and Formaldehyde (H2CO) reacts with oxygen to form CO2 and H2O. How many moles of CO2 will be produced from H2O. How many moles of CO2 will be produced from reacting 2 moles of H2CO with oxygen?reacting 2 moles of H2CO with oxygen?A A 11B B 2 2 C C 44D D 88

NN22 + 3H + 3H22 → → 2NH2NH33

If 6 liters of hydrogen gas are used,how many liters of If 6 liters of hydrogen gas are used,how many liters of nitrogen gas will benitrogen gas will be

needed for the above reaction at STP?needed for the above reaction at STP?A A 2 liters 2 liters B B 3 liters3 litersC C 4 liters4 litersD D 12 liters12 liters

2KOH + H2KOH + H22SOSO44 → → 2H2H22O O + + KK22SOSO44

What mass of potassium hydroxide is required to react What mass of potassium hydroxide is required to react completely with 2.70 g of sulfuric acid to produce potassium completely with 2.70 g of sulfuric acid to produce potassium sulfate and water?sulfate and water?A A 4.73 g4.73 gB B 3.09 g 3.09 g C C 2.36 g2.36 gD D 1.54 g1.54 g


Solution Concentrations

Calculating molarity:

Memorize this equation: Molarity = moles/liters or M = mol L

Memorize conversion factor: 1000 mL = 1 L

Some example of using this equation:

Example 1: the molarity of 2.0 moles of HCl in a 0.50 L solution of water is:

molarity = 2.0 mole HCl/0.50 L = 4.0 Molar or 4 M

Example 2: The molarity of 0.40 moles of HCl in a 300. mL L solution of water is:

molarity = 0.40 moles HCl/0.300. L = = 1.3 M



Example 3:

The molarity of 72.9 g of HCl in 5.0 liters of aqueous solution is:

Answer: first calculate the moles of HCl

72.9 g HCl72.9 g HCl xx 1 mol HCl1 mol HCl = = 2.00 mol HCl2.00 mol HCl

36.46 g HCl36.46 g HCl

Then calculate molarity of solution:

2.00 mol HCl/5.0 L = 0.40 M HCl



You try one:

What is the molarity of 1.2 grams LiF in a 50. mL aqeous solution?

Answer: first calculate the moles of LiF

1.2 g LiF1.2 g LiF xx 1 mol LiF1 mol LiF = = 0.046 mol LiF0.046 mol LiF

25.94 g 25.94 g LiFLiF

Then calculate molarity of solution (remember convert mL to Liters):

0.046 mol LiF/0.050 L = 0.95 M LiF



Diluting concentrated solutions

Memorize: C1V1 = C2V2

•C1 and V1 are the beginning molarities and volumes

•C2 and V2 are the ending molarities and volumes

•V1 and V2 can be in Liters or mLs, but must be the same units for both

Example:

What is the molarity of a 10. mL sample of 2.0 M aqueous HCl diluted to 40. mL

Answer:

(2.0)(10.) = (M2)(40.) so M2 = 0.5 Molar HCl



Diluting concentrated solutions

Memorize: C1V1 = C2V2

•C1 and V1 are the beginning molarities and volumes

•C2 and V2 are the ending molarities and volumes

•V1 and V2 can be in Liters or mLs, but must be the same units for both

You try one:

How many milliliters of 6.0 Molar HCl are required to prepare 240 mL of 2.0 Molar HCl?

Answer:

(6.0)(V1) = (2.0)(240) so V1 = 80. mL HCl

How many milliliters of 2.00 M H2SO4 are needed How many milliliters of 2.00 M H2SO4 are needed to provide 0.250 mole of H2SO4?to provide 0.250 mole of H2SO4?AA 125 mL 125 mL BB 1.25 x 101 mL1.25 x 101 mLCC 8.00 x 103 mL8.00 x 103 mLDD 8.00 mL8.00 mL

What is the molarity of a solution prepared by What is the molarity of a solution prepared by dissolving 27.2 g of sodium chloride in enough dissolving 27.2 g of sodium chloride in enough water to prepare 500.0 mL of solution?water to prepare 500.0 mL of solution?AA 0.186 M0.186 MBB 0.465 M0.465 MCC 0.930 M 0.930 M DD 1.860 M1.860 M

A solution contains 225 g of glucose, C6H12O6, A solution contains 225 g of glucose, C6H12O6, dissolved in enough water to make 0.825 L of dissolved in enough water to make 0.825 L of solution. What is the molarity of the solution?solution. What is the molarity of the solution?AA 0.66 M0.66 MBB 0.97 M0.97 MCC 1.03 M1.03 MDD 1.52 M 1.52 M

Chemistry SOL Review--Molar Relationships

Chemical Equilibrium

Exothermic and Endothermic Reactions

Exothermic reactions release heat

Endothermic reactions absorb heat

0

100

rxn progress >

Jou

les

>

0

100

rxn progress >

Joul

es >

A + B = AB + heat A + B + heat = AB

Catalysts lower the Activation energy barrier, making reactions faster.

http://jchemed.chem.wisc.edu/JCESoft/CCA/pirelli/pages/cca6hotglass.html



Reversible Reactions

Some reactions are REVERSIBLE, which means that they can go backwards (from product to reactant)

Example: The reaction between nitrogen and hydrogen, where a “” indicates a reversible reaction

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

The forward reaction takes place at the same rate as the reverse reaction. The equilibrium position of products and reactants depends on the conditions of the reaction. If we change the reaction conditions, the equilibrium changes.

“UP UP AND AWAY!”




Le Chatelier’s Principle: If a system at equilibrium is stressed, the equilibrium will shift in a direction that relieves that stress.

Equilibrium will shift AWAY from what is added. Here, N2 is added.

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

N2 More “product” made






Equilibrium will shift AWAY from what is added. Here, NH3 is added.

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

NH3More “reactants” made






Equilibrium will shift TOWARDS what is removed. Here H2 is removed.

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

H2

More “reactants” made





Equilibrium will shift TOWARDS what is removed. Here heat is removed.

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

heat

More “product” made



Methods to Speed up Reactions:

•Use a catalyst

•Reduce the particle size

•Increase the heat

•Increase reactant concentration

http://jchemed.chem.wisc.edu/JCESoft/CCA/pirelli/pages/cca2icebomb.html

In the reaction 2SO2 (g)In the reaction 2SO2 (g) + + O2 (g) O2 (g) 2SO3 (g), which change would cause the 2SO3 (g), which change would cause the greatest increase in the concentration of greatest increase in the concentration of SO3?SO3?AA Decrease the concentration of SODecrease the concentration of SO22BB Decrease the concentration of ODecrease the concentration of O22CC Increase the concentration of SOIncrease the concentration of SO22 DD Increase the concentration of OIncrease the concentration of O22

Which condition will cause a shift inWhich condition will cause a shift inthe equilibrium of the above reaction?the equilibrium of the above reaction?

A A Double the concentration of reactants Double the concentration of reactants and productsand productsB B Increase the reaction temperature Increase the reaction temperature C C Reduce the concentration of products Reduce the concentration of products and reactants by and reactants by 10%10%D D Keep the reaction temperature constantKeep the reaction temperature constant


Acid/Base Theory

Acids and BasesGeneric formula for acids = HX (HCl, HNO3, H2SO4)

Generic formula for bases = MOH where M is any metal (NaOH, KOH, Ca(OH)2 Ammonia, NH3, is also a base.

Acid solutions have a pH less than 7

Basic solutions have a pH more than 7

Arrhenius acids:Taste _______ turn litmus paper red.

Arrhenius bases Taste _______Feel __________Turn litmus paper blue.

sour

bitterslippery

SAFETY NOTES

Always add acid to water when diluting (AAA)

If you spill acid or base on yourself, rinse with lots of water.

http://jchemed.chem.wisc.edu/JCESoft/CCA/pirelli/pages/cca5denature1.html


Acid/Base Theory

What is pH?

pH indicates the hydrogen ion molarity [H+] in a solution

pH = -log[H+]

pOH indicates the hydroxide ion molarity [OH-] in a solution.

pOH = -log[OH-]

Example: A 1.0 x 10-3 molar solution of HCl would have a pH of ___

Example: A 1.0 x 10-4 molar solution of KOH would have a pOH of ___

Memorize: pH + pOH = 14.

Example: A solution with a pH of 8 will have a pOH of: ____.

3

4

6

Which pair of solutions would be acidic if mixed in Which pair of solutions would be acidic if mixed in equal quantities?equal quantities?A A A and B A and B B B B and CB and CC C B and DB and DD D C and DC and D

What is represented by the pH of a solution?What is represented by the pH of a solution?AA Partial pressure of hydrogen ions in the solutionPartial pressure of hydrogen ions in the solutionB B Electronegativity of dissociated hydrogen ions in the Electronegativity of dissociated hydrogen ions in the solutionsolutionC C Concentration of hydrogen ions in the solution Concentration of hydrogen ions in the solution D D Temperature of hydrogen ions in the solutionTemperature of hydrogen ions in the solution

The hydrogen ion concentration is 1 x 10The hydrogen ion concentration is 1 x 10-7-7. What is the pH of . What is the pH of this solution?this solution?AA 11BB 7 7 CC 1010DD 1414

SolutioSolutionn

AA BB CC DD

pHpH 22 66 99 1212

Ulcers are often caused by an excess Ulcers are often caused by an excess of stomach acid. Milk of magnesia is of stomach acid. Milk of magnesia is often used to soothe the irritation. often used to soothe the irritation. Milk of magnesia is probably —Milk of magnesia is probably —AA an acidan acidBB a base a base CC an indicatoran indicatorDD a colloida colloid

The pH of a 0.1 molar aqueous The pH of a 0.1 molar aqueous solution of HCl would equal —solution of HCl would equal —AA -1-1BB 1 1 CC 1111DD 1313

Documents

Chemistry SOL Review— Molar Relationships The Mole and Mole Calculations The molar mass = the sum of all the atomic masses. Example Ca(NO 3 ) 2 = 40.08