1. Practice Problems Chang, Chapter 4 Reactions in Aqueous Solutions

2. 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

3. 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, moles
% composition
Molarity

4. 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 (Stoichiometry)

5. Terms that can be used as factors for dimensional analysis
Unit conversion equivalences
Percentages (%)
Density
Molar mass
Molar volume
Avogadro’s number
Concentration expressions
Ratios, mole ratios

6. The following exercises are a review of basic calculations done in Chapter 3 as a foundation for dong problems in Chapter 4

7. 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?

8. 3.2 Avogadro’s Number & the Molar Mass of an Element
Calculate the number of grams of lead (Pb) in 12.4 moles of lead.

9. 3.2 Avogadro’s Number & the Molar Mass of an Element
Calculate the number of atoms in g of potassium (K).

10. What is the molecular mass of methanol (CH4O)?

11. 3.3 Molecular Mass
Calculate the number of moles of chloroform (CHCl3) in 198 g of chloroform.

12. 3.3 Molecular Mass
How many H atoms are in 72.5 g of isopropanol (rubbing alcohol), C3H8O?

13. 3.5 Percent Composition of Compounds
Calculate the percent composition by mass of each of the elements in sulfuric acid (H2SO4).

14. 3.5 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%.

15. 3.5 Percent Composition of Compounds
Calculate the number of grams of Al in 371 g of Al2O3.

16. 3.6 Experimental Determination of Empirical Formulas
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?

17. 3.7 Chemical Reactions & Chemical Equations
Balance the equation representing the reaction between iron(III) oxide, Fe2O3, & carbon monoxide (CO) to yield iron (Fe) & carbon dioxide (CO2).

18. 3.8 Amounts of Reactants & Products
Methanol (CH3OH) burns in air according to the equation
2CH3OH + 3O2 → 2CO2 + 4H2O
If 209 g of methanol are used up in a combustion process, what is the mass of H2O produced?

19. 3.8 Amounts of Reactants & Products
The reaction between nitric oxide (NO) and oxygen to form nitrogen dioxide (NO2) is a key step in photochemical smog formation: 2NO(g) + O2(g) → 2NO2(g) How many grams of O2 are needed to produce 2.21 g of NO2?

20. 3.9 Limiting Reagents
The reaction between aluminum and iron(III) oxide can generate temperatures approaching 3000°C and is used in welding metals: 2Al + Fe2O3 → Al2O3 + 2Fe In one process, 124 g of Al are reacted with 601 g of Fe2O3. (a) Calculate the mass (in grams) of Al2O3 formed. (b) How much of the excess reagent is left at the end of the reaction?

21. 3.10 Reaction Yield
Industrially, vanadium metal, which is used in steel alloys, can be obtained by reacting vanadium(V) oxide with calcium at high temperatures: 5Ca + V2O5 → 5CaO + 2V In one process, 1.54 x 103 g of V2O5 react with 1.96 x 103 g of Ca. (a) Calculate the theoretical yield of V. (b) Calculate the percent yield if 803 g of V are obtained.

22. Solutions and Reactions
The important thing to remember is that substances exist in different forms in solution

23. 4.2 Precipitation Reactions
Classify the following ionic compounds as soluble or insoluble:
a) CuS
b) Ca(OH)2
c) Zn(NO3)2

24. 4.2 Precipitation Reactions
Predict the precipitate produced by mixing an Al(NO3)3 solution with a NaOH solution. Write the net ionic equation for the reaction.

25. Classify each of the following species as a Bronsted acid or base:
4.3 Acid-Base Reactions
Classify each of the following species as a Bronsted acid or base:
a) SO42-
b) HI

26. 4.4 Oxidation-Reduction Reactions
Assign oxidation numbers to all of the elements in the following compound and ion:
a) PF3
b) MnO4-

27. 4.4 Oxidation-Reduction Reactions
Identify the following redox reactions by type:
a) Fe + H2SO4 → FeSO4 + H2
b) S + 3F2 → SF6
c) 2CuCl → Cu + CuCl2
d) 2Ag + PtCl2 → 2AgCl + Pt

28. 4.5 Concentration of Solutions
What is the molarity of an 85.0 mL ethanol (C2H5OH) solution containing 1.77 g of ethanol?

29. 4.5 Concentration of Solutions
What volume (in milliliters) of a M NaOH solution contains 6.22 g of NaOH?

30. 4.5 Concentration of Solutions
How would you prepare 2.00 x 102 mL of a M NaOH solution, starting with a 5.07 M stock solution?

31. 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

32. 4.6 Gravimetric Analysis
A sample of g of an ionic compound containing the bromide ion (Br-) is dissolved in water and treated with an excess of AgNO3. If the mass of the AgBr precipitate that forms is g, what is the percent by mass of Br in the original compound?

33. 4.7 Acid-Base Titrations
How many grams of KHP (KHC8H4O4 ) are needed to neutralize mL of a M NaOH solution?
KHC8H4O4(aq) + NaOH(aq) → KNaC8H4O4(aq) + H2O(l)
KHC8H4O4 molar mass = g

34. 4.7 Acid-Base Titrations
How many milliliters of a 1.28 M H2SO4 solution are needed to neutralize 60.2 mL of a M KOH solution?

35. 10HI + 2KMnO4 + 3H2SO4 → 5I2 + 2MnSO4 + K2SO4 + 8H2O
4.8 Redox Titrations
How many milliliters of a M HI solution are needed to reduce 22.5 mL of a M KMnO4 solution according to the following equation:
10HI + 2KMnO4 + 3H2SO4 → 5I2 + 2MnSO4 + K2SO4 + 8H2O

36. According to the following balanced reaction, how many moles of NO are formed from 8.44 moles of NO2 if there is plenty of water present? 3 NO2(g) + H2O(l) → 2 HNO3(aq) + NO(g)

37. A g sample of N2 reacts with 3.02 g of H2 to form ammonia (NH3). If ammonia is the only product, what mass of ammonia is formed?