Practice Problems Quantitative Aspects

How to keep things straight when solving quantitative problems: First identify what you are being asked to find – If it is not clear to you what the problem asks, list down the data or information you are provided with Connect this with a formula, a definition or a topic you have learned about Find out if you have all the information you need to use the formula. If not, find other information or other formulas that can be used to supply the missing information Check out the units. Find conversion factors or equivalences if necessary 1

Typical quantitative problems Questions based on defined terms – Atomic mass, molar mass – Average atomic mass of an element – Avogadro’s number – Molar volume Questions based on formulas – Density, volume, mass, # of moles – % composition – Empirical and molecular formulas – Balancing and Interpreting Chemical Equations 2

Questions based on the Chemical formula Given the formula, find the amount of one of its components Given a component in a formula, find the amount Questions based on the balanced chemical equation: Proportions, mole ratios 3

FYI: Terms that can be used as factors for dimensional analysis Conversion units(equivalences) Percentages (%) Density Molar mass Molar volume Avogadro’s number Mass ratios, mole ratios 4

3.2 Avogadro’s Number & the Molar Mass of an Element How many moles of magnesium (Mg) are there in 87.3 g of Mg? 5

Calculate the number of grams of lead (Pb) in 12.4 moles of lead Avogadro’s Number & the Molar Mass of an Element

Calculate the number of atoms in g of potassium (K) Avogadro’s Number & the Molar Mass of an Element

What is the molecular mass of methanol (CH 4 O)? Molecular Mass

Calculate the number of moles of chloroform (CHCl 3 ) in 198 g of chloroform Molecular Mass

How many H atoms are in 72.5 g of isopropanol (rubbing alcohol), C 3 H 8 O? Molecular Mass

Calculate the percent composition by mass of each of the elements in sulfuric acid (H 2 SO 4 ) Percent Composition of Compounds

Determine the empirical formula of a compound having the following percent composition by mass: K: 24.75%; Mn: 34.77%; O: 40.51% Percent Composition of Compounds

Calculate the number of grams of Al in 371 g of Al 2 O Percent Composition of Compounds

A sample of a compound containing boron (B) and hydrogen (H) contains g of B & g of H. The molar mass of the compound is about 30 g. What is its molecular formula? Experimental Determination of Empirical Formulas

Balance the equation representing the reaction between iron(III) oxide, Fe 2 O 3, & carbon monoxide (CO) to yield iron (Fe) & carbon dioxide (CO 2 ) Chemical Reactions & Chemical Equations

Methanol (CH 3 OH) burns in air according to the equation 2CH 3 OH + 3O 2 → 2CO 2 + 4H 2 O If 209 moles of methanol are used up in a combustion process, what is the number of moles of H 2 O produced? Amounts of Reactants & Products (Intro to Chapter 4)

3.11 Practice Writing and Balancing Equations; Identifying Type of Rxn Worksheet posted See also Notes on Types of Chemical Equations (Discussed in Lab March 4) END Test 2 Practice 17

The reaction between nitric oxide (NO) and oxygen to form nitrogen dioxide (NO 2 ) is a key step in photochemical smog formation: 2NO(g) + O 2 (g) → 2NO 2 (g) How many grams of O 2 are needed to produce 2.21 g of NO 2 ? 18 CHAPTER 4 Start : Amounts of Reactants & Products

The reaction between aluminum and iron(III) oxide can generate temperatures approaching 3000°C and is used in welding metals: 2Al + Fe 2 O 3 → Al 2 O 3 + 2Fe In one process, 124 g of Al are reacted with 601 g of Fe 2 O 3. (a) Calculate the mass (in grams) of Al 2 O 3 formed. (b) How much of the excess reagent is left at the end of the reaction? 19 Limiting Reagents CHAPTER 4

Industrially, vanadium metal, which is used in steel alloys, can be obtained by reacting vanadium(V) oxide with calcium at high temperatures: 5Ca + V 2 O 5 → 5CaO + 2V In one process, 1.54 x 10 3 g of V 2 O 5 react with 1.96 x 10 3 g of Ca. (a) Calculate the theoretical yield of V. (b) Calculate the percent yield if 803 g of V are obtained Reaction Yield CHAPTER 4

Solutions and Reactions The important thing to remember is that substances exist in different forms in solution 21 CHAPTER 4

4.2 Precipitation Reactions 22 Classify the following ionic compounds as soluble or insoluble: a) CuS b) Ca(OH) 2 c) Zn(NO 3 ) 2 CHAPTER 4

4.2 Precipitation Reactions 23 Predict the precipitate produced by mixing an Al(NO 3 ) 3 solution with a NaOH solution. Write the net ionic equation for the reaction. CHAPTER 4

4.3 Acid-Base Reactions 24 Classify each of the following species as a Bronsted acid or base: a) SO 4 2- b) HI CHAPTER 4

4.4 Oxidation-Reduction Reactions 25 Assign oxidation numbers to all of the elements in the following compound and ion: a) PF 3 b) MnO 4 - CHAPTER 4

4.4 Oxidation-Reduction Reactions 26 Identify the following redox reactions by type: a) Fe + H 2 SO 4 → FeSO 4 + H 2 b) S + 3F 2 → SF 6 c) 2CuCl → Cu + CuCl 2 d) 2Ag + PtCl 2 → 2AgCl + Pt CHAPTER 4

4.5 Concentration of Solutions 27 What is the molarity of an 85.0 mL ethanol (C 2 H 5 OH) solution containing 1.77 g of ethanol? CHAPTER 4

4.5 Concentration of Solutions 28 What volume (in milliliters) of a M NaOH solution contains 6.22 g of NaOH? CHAPTER 4

4.5 Concentration of Solutions 29 How would you prepare 2.00 x 10 2 mL of a M NaOH solution, starting with a 5.07 M stock solution? CHAPTER 4

Solution Stoichiometry Stoichiometry of solutions relies on the same pattern of using the mole ratios from balanced chemical equations When given grams moles can be calculated as usual from molar masses When given solutions, moles can be calculated from M and V 30 CHAPTER 4

4.6 Gravimetric Analysis 31 A sample of g of an ionic compound containing the bromide ion (Br - ) is dissolved in water and treated with an excess of AgNO 3. If the mass of the AgBr precipitate that forms is g, what is the percent by mass of Br in the original compound? CHAPTER 4

4.7 Acid-Base Titrations 32 How many grams of KHP (KHC 8 H 4 O 4 ) are needed to neutralize mL of a M NaOH solution? KHC 8 H 4 O 4 (aq) + NaOH(aq) → KNaC 8 H 4 O 4 (aq) + H 2 O(l) KHC 8 H 4 O 4 molar mass = g CHAPTER 4

4.7 Acid-Base Titrations 33 How many milliliters of a 1.28 M H 2 SO 4 solution are needed to neutralize 60.2 mL of a M KOH solution? CHAPTER 4

4.8 Redox Titrations 34 How many milliliters of a M HI solution are needed to reduce 22.5 mL of a M KMnO 4 solution according to the following equation: 10HI + 2KMnO 4 + 3H 2 SO 4 → 5I 2 + 2MnSO 4 + K 2 SO 4 + 8H 2 O CHAPTER 4

According to the following balanced reaction, how many moles of NO are formed from 8.44 moles of NO 2 if there is plenty of water present? 3 NO 2 (g) + H 2 O(l) → 2 HNO 3 (aq) + NO(g) 35 CHAPTER 4

A g sample of N 2 reacts with 3.02 g of H 2 to form ammonia (NH 3 ). If ammonia is the only product, what mass of ammonia is formed? 36 CHAPTER 4