Date modified: Thu 2023-08-31 . 08:04 PM
Date created: Sat 2023-10-07 . 09:02 PM
# pH and chemistry. In chemistry one measures acid concentration by looking at concentration of hydrogen ions $\text{H}^{+}$. In particular, one denotes the concentration of hydrogen ions by the symbol $[\text{H}^{+}]$, and it is measured in molar concentration with units of mol/L. Here recall 1 mol = 1 Avogadro's number, which is approximately $6.022\times 10^{23}$. And here L denotes liters, which is a volume measure, and 1 L = $1000\text{ cm}^{3}$. So a molecule $X$ with a concentration $[X]$ of 1 mol/L means there is $6.022\times 10^{23}$ molecules of $X$ for every liter of volume, or 1 mol of molecules for every liter of volume. To express acidity, instead of reporting the molar concentration of hydrogen ions one uses the pH scale, where $\text{pH} = -\log_{10}[\text{H}^{+}]$, where $[\text{H}^{+}]$ is measured in mol/L. ![[---images/---assets/---icons/question-icon.svg]] If neutral water is to have a pH of 7, what is the concentration of hydrogen ions? Express in mol/L. ![[---images/---assets/---icons/question-icon.svg]] Two liquids A and B are presented to you. Liquid A has a pH of 9, and liquid B has a pH of 3. Calculate the concentration of hydrogen ions in liquid A and liquid B. Which one has a higher concentration of hydrogen ion? ![[---images/---assets/---icons/question-icon.svg]] Let us define $\text{pX}=-\log_{10}[X]$, where $[X]$ it the molar concentration of $X$ in mol/L. Suppose a 3L of solution with $\text{pX}=4$ is added to a 3L of solution with $\text{pX}=6$. What is the new volume and the new pX of the solution, assuming X does not react at all and this is a simple mixing. Suppose a 3L of solution with $\text{pX}=4$ is added to a 5L of solution with $\text{pX}=6$. What is the new volume and the new pX of the solution, assuming X does not react at all and this is a simple mixing.