Final answer:
Significant digits for pH and pOH are determined by the number of digits after the decimal point, which indicates the precision of the hydrogen or hydroxide ion concentration. For example, a pH of 7.00 has two significant figures. In pH calculations, the resulting pOH will keep the same number of significant figures as the original pH value.
Step-by-step explanation:
Understanding significant digits for pH and pOH calculations is crucial in accurately reporting the concentration of hydrogen or hydroxide ions in a solution. Because the number(s) before the decimal point in the pH value relate to the power on 10, it's the number of digits after the decimal point - the part that is underlined - that determines the number of significant figures in the final answer. For example, a pH of 7.00 indicates two significant figures because there are two digits following the decimal point.
Let's look at several examples to discern significant figures in pH calculations:
pH = -log [1 × 10⁻³] = 3.0, which has one decimal place, indicating that 1 has one significant figure.
pH = -log [2.5 ×10⁻¹¹] = 10.60, which has two decimal places, showing that 2.5 has two significant figures.
pH = -log [4.7 ×10⁻⁹] = 8.30, which has two decimal places, similarly indicating two significant figures for 4.7.
In a pH calculation, the resulting pOH is the difference after subtracting from 14. The answer will maintain the same number of significant figures as the initial pH value.