With $3g$ of an unknown monoprotic weak base, $50ml$ of solution is made. $15ml$ of this

solution is titrated with a $0\mathrm{.}1M$ nitric acid solution the equivalence point of this titration is

reached after adding $35ml$ of the nitric acid solution. The $pH$ at the equivalence point is $4\mathrm{.}7.$

Calculate the basicity constant of the unknown weak base. Assume volumes are additive

$(10$ pts$){?}^{\text{d}\text{a}\text{r}\text{r}}longrightarro{w}^{K_b}H{O}_3$

How should be answered?

Write the titration reaction, this is a reaction that goes to completion

Recall that the equivalence point is defined as the point at which the reactants have reacted

according to the stoichiometry of the reaction i$.$e$.$ the reactants are $($both$)$ just completely

consumed. This means that at the end of the titration reaction all weak base $($B$)$ has been

converted into its conjugate acid $(B{H}^{+}).$ So at that moment there are only conjugated acid ions

and nitrate ions in the solution. The nitrate ions do not affect the $pH,$ but the conjugate acid of a

weak base is itself a weak acid that will react with water.

Calculate the molarity of the conjugate acid and calculate its acid constant by writing the

equilibrium reaction of the weak acid with water, here you know the initial concentration of

the acid and the equilibrium concentration of the reaction products since you know the $pH$

from which you calculate the $H^{+}.$

Calculate $K_b$ of the weak base using. $K_w=K_{a}x{K}_b$

What usually went wrong?

The formula of nitric acid was wrong

The titration reaction was considered to be an equilibrium reaction and the I,C$,$E method used.

please show every step to solve