Question 10.6: The pH of a solution is 6.80. What is the molar hydronium io......
The pH of a solution is 6.80. What is the molar hydronium ion concentration for this solution?
From the defi ning equation for pH, we have
pH = -log [H_{3}O^{+}] = 6.80
log [H_{3}O^{+}] = -6.80
To find [H_{3}O^{+}], we need to determine the antilog of -6.80.
How an antilog is obtained using a calculator depends on the type of calculator. Many calculators have an antilog function (sometimes labeled INV log) that performs this operation. If this key is present, then
1. Enter the number -6.80. Note that it is the negative of the pH that is entered into the
calculator.
2. Press the INV log key (or an inverse key and then a log key). The result is the desired
hydronium ion concentration.
log [H_{3}O^{+}] = -6.80
antilog [H_{3}O^{+}] = 1.5848931 × 10^{-7}
\quadRounded off, this value translates into a hydronium ion concentration of 1.6 × 10^{-7} M.
Some calculators use a 10^{x} key to perform the antilog operation. Use of this key is based on the mathematical identity
antilog x = 10^{x}
In our case, this means
antilog -6.80 = 10^{-6.80}
If the 10^{x} key is present, then
1. Enter the number -6.80 (the negative of the pH).
2. Press the function key 10^{x}. The result is the desired hydronium ion concentration.