massa Na2CO3 (Mr=106) yang harus dilarutkan dalam 200 mL air agar diperoleh pH = 10 (Ka=10-5)

pH = 10
pOH = 4
OH- = 10-4 M

OH- = akar Kw/Ka [G]
10-4 = akar 10-14/10-5 [G]
10-8 = 10-9 [G]
[G] = 10 M

M = m/Mr x 1000/v
10 = m/106 x 1000/200
m = 212 gram