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Chemistry 122 (General College Chemistry I)- Fall 2021
Discussion Worksheet Week 3
Topics: empirical and molecular formulas, writing and balancing chemical equations,
stoichiometry of formulas and equations, limiting reactants and yields
Relevant Chapters in Silberberg, 9e: Chapter 3.2-3.4
Student Directions: Try all problems with your best effort and submit your completed work to
Assignments by the due date. Use your text as a resource for any constants or relationships
needed which are not given in the problem. NOTE: Some answers are shown in brackets.
You may have to work ahead depending on your discussion day. When topics are fully
covered in lecture, go back and redo problems you did not understand. Practice problem
solving!
1. You are asked to determine the empirical and molecular formulas of an unknown white
powder. The powder contains only carbon, hydrogen, and oxygen. A 3.786 g sample of the
powder (molar mass = 270.36 g/mol) was subjected to combustion analysis. When
combustion was complete, 11.09 g of CO2 and 2.776 g of H2O were collected.
a) Determine the empirical formula.
[C! H"" O]
b) Determine the molecular formula
[C"# H$$ O$ ]
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2. During combustion analysis, the unknown white powder in problem 2 was burned in the
presence of oxygen gas to produce gaseous carbon dioxide and gaseous water.
a) Write a complete, balanced chemical equation for this reaction. (Use the molecular formula
of the unknown powder in your equation.)
b) Using the balanced equation, calculate how much oxygen gas (in grams) is required to
completely combust 3.786 grams of the white powder?
[10.08 g]
3. Balance the following equations. (Include states of matter for parts c and d.)
a) RuBr3 + CO + Ag → Ru(CO)5 + AgBr
b) NH% NO& → N$ + O$ + H$ O
c) Write a balanced equation for the reaction of solid sulfur (S# ) with chlorine gas to produce
gaseous sulfur hexachloride.
d) Write a balanced equation for the reaction of aqueous potassium hydroxide with aqueous
iron (III) nitrate to form solid iron (III) hydroxide and aqueous potassium nitrate.
4. Liquid disilicon hexachloride (1.10 mol) reacts with liquid water (2.10 mol) to produce solid
silicon dioxide, hydrogen chloride gas and hydrogen gas. The reaction goes to completion.
a) Write a balanced equation for this reaction.
b) Which reactant is the limiting reactant? Show work.
c) Which reactant is the excess reactant? ___________________
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d) How many moles of limiting reactant remain when the reaction is complete? Explain your
answer.
[0 mol]
e) How many moles of excess reactant remain when the reaction is complete? [0.575 mol]
5. Cisplatin, Pt(NH& )$ Cl$ , is a chermotherapy medication used to treat many types of cancer. It is
prepared as follows:
K $ PtCl% + 2 NH& → 2 KCl + Pt(NH& )$ Cl$
a) When 64.8 g of K $ PtCl% is reacted with 44.6 g of NH& , how many grams of cisplatin are
produced?
[47.0 g]
b) When this reaction was carried out in the lab, the percent yield for cisplatin was 88.0 %.
How many grams of cisplatin were produced in the lab?
[41.4 g]