Question

you are assigned the task of determining the identity of an unknown weak base. if a 4.70x10^-6 M solution of the weak base has a pH of 7.820, determine the kb value of the weak base.

answer = 1.08x10^-7

however i keep getting 9.29x10^-8

how do i solve

Answer #1

**Answer** - We are given, [B] =
4.70*10^{-6} M, pH = 7.820

We know,

pH +pOH = 14

so, pOH = 14 -pH

= 14 – 7.820

= 6.18

So, [OH^{-}] = 10^{-pOH}

= 10^{-6.18}

= 6.61*10^{-7} M

So at equilibrium , x = [OH^{-}] = 6.61*10^{-7}
M

So, Kb = [OH^{-}][BH^{+}] / [B]

[B] = 4.70*10^{-6} M – 6.61*10^{-7} M

=
4.04*10^{-6} M

**Kb** = 6.61*10^{-7} *
6.61*10^{-7} / 4.04*10^{-6}

=
**1.08*10 ^{-7}**

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A student was assigned the task of determining the identity of
an unknown liquid. The student weighed a clean, dry 250-mL
Erlenmeyer flask. The student completely filled the flask with
water. He then proceeded to weigh the flask containing the
water.
Mass of 250-mL Erlenmeyer flask: 78.639 g
Mass of 250-mL Erlenmeyer flask and water: 327.039 g
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± Determining the pH of a Weak Base and the Percent Ionization
of a Weak Acid
Unlike strong acids and bases that ionize completely in
solution, weak acids or bases partially ionize. The tendency of a
weak acid or base to ionize can be quantified in several ways
including
Ka or Kb,
pKa or pKb,
and percent ionization*.
*This assumes that species of equal concentrations are being
compared as percent ionization is affected by concentration.
Part A
Pyridine is a...

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ph=
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