1. Calculate the concentration of the 25mL of phosphoric acid Which is neutraliz

Question

1. Calculate the concentration of the 25mL of phosphoric acid Which is neutralized with 7.8 mL of 0.2M NaOH?

2. In a solution of NH3, the concentration of NH3 is 0.01 M, Kb is 1.8 x 10-5. What is the concentration of the hydroxide ion? NH3 NH4 ++ OH-

3. Calculate the Ka for formic acid, HCHO2 if the H+ concentration is 1.5 x 10-3 M and the concentration of the HCHO2 is 0.0125M at equilibrium.

4. The ionization constant for the weak acid HA is 4.0 x 10-8. Calculate the equilibrium concentration of H+, A- and HA in a 0.050 M solution of the acid.

Explanation / Answer

1) H3PO4 + 3 NaOH -------------------> Na3PO4 + 3H2O

M1 V1 / n1 = M2 V2 / n2

M1 x 25 / 1 = 0.2 x 7.8 / 3

M1 = 0.0208 M

concentration of the 25mL of phosphoric acid = 0.0208 M

2)

[OH-] = sqrt (Kb x C) = sqrt (1.8 x 10^-5 x 0.01)

       = 4.24 x 10^-4 M

3)

HCHO2 --------------------> H+ + CHO2-

0.0125-x                             x            x

x = 1.5 x 10^-3

Ka = x^2 / 0.0125 -x

Ka = (1.5 x 10^-3)^2 / (0.0125 -1.5 x 10^-3)

Ka = 2.05 x 10^-4

4)

[H+] = [A-] = sqrt (Ka x C)

                    = sqrt (4.0 x 10^-8 x 0.050)

                   = 4.47 x 10^-5 M

[H+] = [A-] =4.47 x 10^-5 M

[HA] = 0.05 -4.47 x 10^-5 = 0.0499 M

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.