Review for chapter 8Review for chapter 8

Problem-solving practiceProblem-solving practice

Calculating massesCalculating masses

1)1) Calculate the molecular mass of Calculate the molecular mass of pentanepentane

2)2) Calculate the formula mass of calcium Calculate the formula mass of calcium sulfatesulfate

3)3) Calculate the molar mass of sodium Calculate the molar mass of sodium carbonatecarbonate

Answers: 1) CAnswers: 1) C55HH1212 = 72.1 u = 72.1 u

2) CaSO2) CaSO44 = 136.2 u = 136.2 u

3) Na3) Na22COCO33 = 106.0 g = 106.0 g

Conversions Conversions

1)1) What is the mass of 7.20 moles of COWhat is the mass of 7.20 moles of CO22??

2)2) How many moles of water molecules How many moles of water molecules are there in 212 grams of water?are there in 212 grams of water?

3)3) How many formula units are there in How many formula units are there in 5.00 moles of NaCl?5.00 moles of NaCl?

Answers: 1) 7.20 moles COAnswers: 1) 7.20 moles CO22 = 317 g CO = 317 g CO22

2) 212 g H2) 212 g H22O = 11.8 moles HO = 11.8 moles H22OO

3) 5.00 moles NaCl = 3.01 x 103) 5.00 moles NaCl = 3.01 x 102424

Percent CompositionPercent Composition

1)1) Calculate the percent composition of Calculate the percent composition of potassium chromatepotassium chromate

2)2) Which has a higher % of oxygen: Which has a higher % of oxygen: potassium chromate or carbon potassium chromate or carbon dioxide?dioxide?

Answers:Answers:

1) 40.3% K, 26.8% Cr, 33.0% O1) 40.3% K, 26.8% Cr, 33.0% O

2) CO2) CO22 has 72.7% O, higher than has 72.7% O, higher than KK22CrOCrO44

Empirical FormulaEmpirical Formula

1)1) What is the empirical formula for a What is the empirical formula for a compound that is 43.7% phosphorus and compound that is 43.7% phosphorus and 56.3% oxygen? Name the compound.56.3% oxygen? Name the compound.

2)2) Name the compound whose composition Name the compound whose composition is 36.5% Na, 25.4% S, and 38.1% O.is 36.5% Na, 25.4% S, and 38.1% O.

Answers:Answers:

1) P1) P22OO55, diphosphorus pentaoxide, diphosphorus pentaoxide

2) Na2) Na22SOSO33, sodium sulfite, sodium sulfite

Molecular formulaMolecular formula

A compound’s empirical formula is A compound’s empirical formula is CHCH33, and its molar mass is 75.0 g. , and its molar mass is 75.0 g. What is its molecular formula?What is its molecular formula?

Answer: CAnswer: C55HH1515

Hydrate FormulaHydrate Formula

A hydrate is found to be 54.3% A hydrate is found to be 54.3% cobalt(II) chloride and 45.7% water. cobalt(II) chloride and 45.7% water. Calculate the empirical formula of Calculate the empirical formula of the hydrate, and name it.the hydrate, and name it.

Answer: CoClAnswer: CoCl22 * 6 H * 6 H22OO

cobalt(II) chloride cobalt(II) chloride hexahydratehexahydrate

Molarity Molarity

1)1) Find the molarity of a solution made Find the molarity of a solution made with 90.0 grams of NaOH in 500. mL with 90.0 grams of NaOH in 500. mL

2)2) How many grams of NaOH are needed How many grams of NaOH are needed to make 100. mL of 0.25 M NaOH?to make 100. mL of 0.25 M NaOH?

3)3) How many mL of 2.00 M NaOH can be How many mL of 2.00 M NaOH can be made with 60.0 g of NaOH?made with 60.0 g of NaOH?

Answers: 1) 4.50 M NaOHAnswers: 1) 4.50 M NaOH 2) 1.00 g NaOH2) 1.00 g NaOH 3) 750. mL of 2.00 M NaOH3) 750. mL of 2.00 M NaOH