pH is a logarithmic scale used to indicate the hydrogen ion concentration, [H^+]
ID: 525240 • Letter: P
Question
pH is a logarithmic scale used to indicate the hydrogen ion concentration, [H^+], of a solution: pH = log[H^+] Due to the autoionization of water, in any aqueous solution, the hydrogen ion concentration and the hydroxide ion concentration, [OH^-], are related to each other by the K_w of water. K_w = [H^+][OH^-] = 1.00 times 10^-14 where 1.00 times 10^-14 is the value at approximately 297 K. Based on this relation, the pH and pOH are also related to each other as 14.00 = pH + pOH 0.90 g of sodium hydroxide (NaOH) pellets are dissolved in water to make 7.5 L of solution. What is the pH of this solution? Express the pH numerically to two decimal places. pH = 11.48 What is the pOH of the solution in Part B? Express the pOH numerically to two decimal places. pOH =Explanation / Answer
Part B: 0.90 g of NaOH dissolved in 7.5 L.
No. moles of NaOH = wt/mol.wt = 0.90 g/ 40.0 (g/mol) = 0.0225 mol
molarity of NaOH = [OH-] = no. moles / volume in L = 0.0225 mol/7.5 L = 0.003 M
Kw = [H+][OH-]
[H+] = Kw/[OH-] = 1.00 x 10^-14/0.003 =3.333 x 10^-12 M
pH = -log[H+] = -log[3.333 x 10^-12] = 11.48
pH = 11.48
Part B:
14.00 = pH + pOH
pOH = 14.00 - pH = 14.00 - 11.48 = 2.52
pOH = 2.52
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