Find the pH of 6.78 times 10^2 M Ca(OH)_2. (Strong bases dissociate completely)

Question

Find the pH of 6.78 times 10^2 M Ca(OH)_2. (Strong bases dissociate completely) So the final concentrations are If you had the some concentration of NaoH and Ca(oH)_2 which one would have the higher pH? Why? Explain. Determine the pH of a 1.09% by mass HCI solution with a density of 1.01 g/ml. What is the mass of HI should be present in 0.250 L of solution to obtain a solution to obtain a solution with a pH of 1.75? 3) What is the mass of NaOH should be present in 0.250 L of solution to obtain a solution to obtain a solution with a pH of 12.36? 4) What is the mass of Ca(OH)_2 should be present in 0.250 L of solution to obtain a solution with a pH of 13.06?

Explanation / Answer

challenge questions :

1) molarity = wt % x density x 10 / molar mass

                  = 1.09 x 1.01 x 10 / 36.5

                 = 0.302 M

HCl = 0.302 M

[H+] = 0.302 M

pH = -log [H+] = -log (0.302)

pH = 0.52

2)

[H+] = 10^-pH = 10^-1.75 = 0.0178 M

molarity = (mass / molar mass ) x 1/ volume

0.0178 = (mass / 127.9) x (1/ 0.250)

mass = 0.57 g

3)

pH = 12.36

pH + pOH = 14

pOH = 1.64

[OH-] = 10^-1.64 = 0.0229 M

NaOH molarity = 0.0229 M

molarity = (mass / molar mass ) x 1/ volume

0.0229 = mass / 40 ) x 1/ 0.250

mass = 0.229 g

4)

[OH-] = 0.1148 M

molarity = (mass / molar mass) x 1/ volume

0.1148 = (mass / 74) x 1 /0.250

mass = 2.127 g

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