Answer
(a) $pH = 1.301$
(b) $pH = -0.7781$
(c) $pH = 14.602$
(d) $pH = 12.301$
Work Step by Step
(a) $HClO_4$: Monoprotic (One $H^+$) strong acid:
$[H_3O^+] = [HClO_4] = 0.050M$
$pH = -log[H_3O^+]$
$pH = -log( 0.05)$
$pH = 1.301$
(b) $HCl$: Monoprotic (One $H^+$) strong acid:
$[H_3O^+] = [HCl] = 6.0M$
$pH = -log[H_3O^+]$
$pH = -log( 6)$
$pH = -0.7781$
(c) $KOH$: Strong base with one $OH^-$:
$[OH^-] = 1 * [KOH] = 4.0M$
$pOH = -log[OH^-]$
$pOH = -log( 4)$
$pOH = -0.602$
$pH + pOH = 14$
$pH + -0.602 = 14$
$pH = 14.602$
(d) $Ba(OH)_2$: Strong base with 2 $OH^-$:
$[OH^-] = 2 * [Ba(OH)_2] = 0.010 * 2 = 0.020M $
$pOH = -log[OH^-]$
$pOH = -log( 0.02)$
$pOH = 1.699$
$pH + pOH = 14$
$pH + 1.699 = 14$
$pH = 12.301$
