The pH of the test tube can be calculated by knowing the concentration of hydrox

Question

The pH of the test tube can be calculated by knowing the concentration of hydroxide ions in solution. The pH = 14 + log10([OH-]). For example, the 0.1 M stock of NaOH has a pH = 14 + log10(0.1) = 13. Using the dilution (5 mL 0.1 NaOH: 5 mL H2O). What is the pH of tube 1? Choose the closest answer. The pH of the test tube can be calculated by knowing the concentration of hydroxide ions in solution. The pH = 14 + log10([OH-]). For example, the 0.1 M stock of NaOH has a pH = 14 + log10([0.1]) = 13. Based on the dilution used, what is the pH of tube 4? Choose the closest answer.

Explanation / Answer

First we have to calculate concentration of hydroxide ion after dilution.

Number of moles of OH- in 5 ml of 0.1 M NaOH = Volume x molarity = 5 x 0.1 = 0.5 mmole

Molarity = number of moles of solute / Volume of solution

Volume (after dilution) = 5 + 5 = 10 ml

[OH-]after dilution = 0.5 / 10 = 0.05 M

pH = 14 + log10([OH-]) = 14 - 1.30 = 12.7

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