**Question 1: **The molar concentration of OH^{–} ions in a certain solution is 1.04 x 10^{-5} mol L^{-1}. Calculate the pOH and then the pH of the solution.

**Question 2: **Death occurs if the pH of human blood plasma changes by more than about ±0.4 from its normal value of about pH = 7.4, the “safe” range is from neutral to slightly alkaline. What is the corresponding range of molar concentrations of hydrogen ions for which human life can be sustained?

**Solution 1: **

**[OH ^{–}] = 1.04 x 10^{-5} mol L^{-1}**

**pOH = – log _{10} (1.04 x 10^{-5}) = 4.98**

**pH + pOH = 14.00**

**pH = 14.00 – 4.98 = 9.02**

**Solution 2:**

Maximum pH = 7.8 | 7.8 = -log_{10}[H^{+}]_{max} | [H^{+}]_{max} = 10^{-7.8} |

Maximum pH = 7.0 | 7.0 = -log_{10}[H^{+}]_{max} | [H^{+}]_{max} = 10^{-7.0} |

From the definition of a logarithm we have [H^{+}] = 10^{-7.8} . The easiest way of solving this on your calculator is to use “shift-log” (which is 10^{x}) then type —7.8 then equals. Take care to use “shift-log” = 10^{x} not “shift-In” = e^{x}.

**[H ^{+}]_{MAX} = 1.58 x 10^{-8} mol L^{-1} **

**[H ^{+}]_{MIN} = 1.00 x 10^{-7} mol L^{-1} **

Human blood covers only a small range of proton concentrations. Here all explanation based on Acid Base Equilibrium.