Worksheet 15
Supplemental Instruction
Iowa State University
Leader: Prina
Course: Chem 177
Instructor: Dr. Greenbowe
Date: 10/08/2014
1) An experiment needs you to use 200.00 ml of 0.262M HBr solution. In your lab however, you
have a stock solution of 4M HBr solution. What procedure will you follow to get the required
concentration of HBr solution needed for this experiment. Also draw a diagram to show this
procedure.
2) N2(g) + 3 H2(g) → 2 NH3(g)
a) Assign oxidation numbers to each of the atoms in the reaction.
N (in N2) =
N (in NH3) =
H (in H2) =
H (in NH3) =
b) When an oxidation number increases, that species has been oxidized. Which reactant
undergoes an increase in its oxidation number?
c) When an oxidation number decreases, that species has been reduced. Which reactant
undergoes an decrease in its oxidation number?
d) The species that is oxidized is called the reducing agent because it gives up an electron, so
hat another species can gain that electron and be reduced. What is the reducing agent in this
equation?
e) What is the oxidizng agent in this reaction?
3) Assign oxidation numbers to the following species and identify and write the oxidation and the
reduction half reaction. Find out the oxidizing and reducing agent and which species looses or
gains electrons.
a) Sr + O2 -> SrO2
b) Cl2 + 2NaBr -> 2NaCl + Br2
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c) 3Mg + N2 -> Mg3N2
d) 4Fe + 3O2 -> 2Fe2O3
4) Calculate the oxidation number of chromium in each of the following.
a. Cr2O3
b. Na2Cr2O7
c. CrSO4
d. Cr2O72-
5) Make sure you know your definitions! Classify the following reactions as acid-base, oxidationreduction, double-displacement, single displacement, decomposition, combustion, precipitation,
gas evolution etc. Choose all that apply.
a) 2HF -> H2 (g) + F 2 (g)
b) Na2SO4 + CaCl2 ----> NaCl + CaSO4
c) Zn + 2 HCl -> ZnCl 2 + H 2
d) NaOH +HCl -> NaCl + H2O
6) How many ml of a 2.5 M NaOH are required to make 250 ml of a 0.5 M NaOH solution.
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