Question

5. Distilled water in equilibrium with air contains dissolved CO2 at a concentration of 1.0x10-5 M. Given that the Keq is 4.47x10-7, calculate the pH of such a solution.

6. If 100 mL of a 0.10M NaOH solution is added to 75mL of a 0.15M HCl solution, then what is the pH of the resultant solution?

7. If the pH of a patient’s blood plasma is 7.2 and the HCO3- concentration is 18 mM, then how much CO2 is dissolved in the blood? The Keq is 4.47x10-7

8. A plasma sample had P(CO2) 28 mm Hg and [HCO3-] 15 mM. What are the pH and the [HCO3-]/[CO2] ratio? Is it more acidic than normal? Use body temperature of 37°C.

9. A buffer solution consists of 0.50 M nitrous acid (HNO2) and 0.60 M sodium nitrite (NaNO2). Ka=4.5x10-4

a) What is the pH of this buffer solution?

b) What is the pH when 10.0 ml of 3.0 M HCl is added to 250 ml of buffer solution?

Answer 1

5)

CO2 + H2O    --------------> H2CO3

concentration of CO2 = 1.0 x 10^-5 M

concentration of H2CO3 = 1.0 x 10^-5 M

H2CO3    ------------------>   H+    +    HCO3-

1.0 x 10^-5                           0              0

1.0 x 10^-5 - x                      x               x

Keq = x^2 / 1.0 x 10^-5 - x

4.47 x 10^-7 = x^2 / 1.0 x 10^-5 - x

x = 1.9 x 10^-6 M

[H+] = 1.9 x 10^-6 M

pH = -log (1.9 x 10^-6 )

pH = 5.72

6) If 100 mL of a 0.10M NaOH solution is added to 75mL of a 0.15M HCl solution, then what is the pH of the resultant solution?

millimoles of NaOH = 100 x 0.1 = 10

millimoles of HCl = 75 x 0.15 = 11.25

millimoles of NaOH < millimooles of HCl

[H+] = 11.25 - 10 / (100 + 75) = 7.14 x 10^-3 M

pH = log ( 7.14 x 10^-3)

pH = 2.15