[Unit 4] Chemical Reactions

[wes-winter]

This question is based on the following reaction.

MnO₄^1-(aq) + 5Fe²⁺(aq) + 8H¹⁺(aq) -> 5Fe³⁺(aq) + Mn²⁺(aq) + 4H₂O(l)

a) Is this reaction an oxidation-reduction reaction? Justify your response by identifying the oxidation states for manganese (Mn).
b) An sample of unknown concentration of potassium permanganate (KMnO₄) is titrated with 25.0 mL of 1.25 M iron (II) nitrate (Fe(NO₃)₂). If the volume of potassium permanganate that was titrated is 12.7 mL, what is its concentration?
c) In a separate reaction, sodium hydroxide (NaOH) it used to standardize the iron (II) nitrate.

2NaOH(aq) + Fe(NO₃)₂(aq) -> Fe(OH)₂(s) + 2NaNO₃(aq)

If 40.0 mL of 0.95 M NaOH reacts with 31.0 mL of 0.65 M Fe(NO₃)₂, then what mass of the precipitate forms?
d) What are three major ions that remain in the filtrate?

[perlaalvarez431]

Side Note: I used a whiteboard but I wouldn’t for the test, I was just too lazy to get out paper

[wes-winter]

Solutions
a) The oxidation state for Mn in MnO₄^1- is +7. The oxidation state for Mn in Mn²⁺ is 2+. The oxidation state for manganese change, therefore, this is a redox reaction.
b)

c)

d) First, the spectator ions are Na¹⁺ and NO₃^1-. They do not participate in the reaction and remain dissolved in solution. The third ion is Fe²⁺. It is part of the excess reactant and while a majority of it ends up in the precipitate, some remains dissolved in solution.