# General Chemistry/Titration and pH/Answers

1. 5.00g of NaOH are dissolved to make 1.00L of solution.

- a) What is the concentration of H
^{+}? (8x10-14 mol/L)

K_{w}= [H^{+}] * [OH^{-}] [H^{+}] = K_{w}/ [OH^{-}]

The concentration of anything is the amount per unit volume:

[NaOH] = amount / volume

The amount of anything can be found from the mass and the molar mass:

amount = mass / mass per mole (molar mass)

We know the mass and we can find the mass per mole, so substitute amount into the above equation:

[NaOH] = amount / volume [NaOH] = ( mass / molar mass ) / volume [NaOH] = mass / ( volume * molar mass )

Since NaOH is a strong base, [OH^{-}] = [NaOH].

Substitute [NaOH] for [OH^{-}] in the above [H^{+}] equation:

[H^{+}] = K_{w}/ [OH^{-}] [H^{+}] = K_{w}/ ( mass / ( volume * molar mass ) [H^{+}] = K_{w}* ( volume * molar mass ) / mass

K_{w}: 1x10^{−14}mol^{2}/L^{2}mass: 5.00g volume: 1.00L molar mass: 40.0g/mol (add up the molar masses of Na, O, and H)

[H^{+}] = 1x10^{−14}mol^{2}/L^{2}* 1.00L * 40.0g/mol / 5.00g [H^{+}] = 40x10^{−14}mol/L * g / 5.00g [H^{+}] = 8x10-14 mol/L

- b) What is the pH? (13.10)

pH = -log_{10}( [H^{+}] / 1M ) pH = -log_{10}( 8x10-14 mol/L / 1 mol/L ) pH = -log_{10}( 8x10-14 ) pH = - ( -13.10 ) pH = 13.10