What is the hydroxide-ion concentration in a solution formed by combining 200.mL of 0.16 M HCl with 300.mL of 0.091 M NaOH at 25°C?
HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

Question

Quizplus · Accepted Answer

First, we need to find how much of each reactant is consumed in the reaction. From the balanced chemical equation, we see that 1 mol of HCl reacts with 1mol of NaOH. Using the concentrations and volumes given, we can find the moles of each reactant:

moles of HCl = (0.16 mol/L)(0.2 L) = 0.032 mol 
moles of NaOH = (0.091 mol/L)(0.3 L) = 0.0273 mol

Since NaOH is the limiting reactant (less moles than HCl), all of it will be used up in the reaction. Therefore, the amount of NaOH that reacts is also 0.0273 mol.

The balanced chemical equation tells us that 1 mol of NaOH reacts with 1 mol of H+ (from HCl) to produce 1 mol of water and 1 mol of Na+ (from NaOH). Therefore, the amount of H+ that reacts is also 0.0273 mol.

Now we can find the concentration of OH- in the solution using this amount of H+. Since water autoionizes to produce equal amounts of H+ and OH- ions, and we know the total volume of the solution, we can use the following equation:

Kw = [H+][OH-] 
1.0 x 10^-14 = (0.0273 mol / (0.2 L + 0.3 L)) x [OH-] 
[OH-] = 1.1 x 10^-12 M

Therefore, the hydroxide-ion concentration in the solution is 1.1 x 10^-12 M.

What Is the Hydroxide-Ion Concentration in a Solution Formed by Combining