Untitled - Kelly Walsh High School

244 CHEMISTRY FOR THE UTTERLY CONFUSED
Quick Tip
We need to deal with the stoichiometry of this reaction. For this reason, we
need to know the moles of each of the reactants. We can find these from the
concentration and the volume of each solution.
Moles HNO2 a
0.0150 mol HNO2 0.300 mol NaOH 1L
Moles NaOH a ba b(25.00 mL)
L 1000 mL
0.00750 mol NaOH
0.150 mol HNO2 1L
ba b(100.00 mL)
L 1000 mL
We will need the moles of HNO 2 in all the remaining steps in this problem. The
moles of NaOH will be changing as we add more. The coefficients in the reaction
are all ones, thus, we can simply compare the moles to find the limiting
reactant. The sodium hydroxide, with the smaller number of moles is limiting.
We can add the mole information to the balanced chemical equation. (The
water, being neutral, will not be tracked.)
HNO2(aq) NaOH(aq) l Na + (aq) NO2 (aq) H2O(l)
Initial moles 0.0150 0.00750 0 0 —
The reaction will decrease the moles of reactants present and increase the moles
of products. This leads to a reacted line in the table. In this line, we subtract the
moles of limiting reactant from each reactant, and add the moles to each product.
HNO2(aq) NaOH(aq) l Na (aq) NO2 (aq) H2O(l)
Initial moles 0.0150 0.00750 0 0 —
Reacted moles 0.00750 0.00750 0.00750 0.00750
Adding each column in this table gives us the post-reaction amounts:
HNO2(aq) NaOH(aq) l Na (aq) NO2 (aq) H2O(l)
Initial moles 0.0150 0.00750 0 0 —
Reacted moles 0.00750 0.00750 0.00750 0.00750
Post-reaction 0.0075 0.00000 0.00750 0.00750
If any of the reactants or products has a coefficient other than one, you should
multiply the moles added or subtracted by this coefficient.