In this question, we have HClO4 and KOH being mixed together and then a final pH being calculated, one way of doing this calculation is by finding out how many moles are being equivalent to each other and how many we have left divided by the total volume, so lets work on that:
HClO4 = 0.200 (volume) * 0.180 (concentration) = 0.036 moles
KOH = 0.270 ( concentration) * 0.150 (volume) = 0.0405
Total volume will be = 0.150+0.200 = 0.350 L
Now we can do the next calculation
(0.036 - 0.0405)/0.350
0.0128
This final value will be placed in the pH formula, which is:
pH = -log [H+]
pH = -log [0.0128]
pH = 1.89, letter D
