Robin the Research scientist prepares 100 mLs of a solution of 100 mM of Tris HCl. What is the pH? and part two for this question
Calculate the pH when the scientist adds 100 ul of 50% NaOH
To calculate the pH of a solution, you need to know the concentration of the acidic or alkaline component, as well as any dissociation constants involved. In the case of Tris HCl, it is commonly used as a buffer in the range of pH 7-9.
Now, let's determine the initial pH of the 100 mM Tris HCl solution:
1. Convert the concentration from mM to M:
100 mM = 0.1 M
2. Tris HCl is a strong acid, which means it completely dissociates in water. The HCl portion of Tris HCl is what contributes to acidity. So, we need to calculate the pH of 0.1 M HCl.
Since Tris HCl is at a concentration of 0.1 M, it will be completely dissociated, resulting in a 0.1 M concentration of H+. The pH of HCl or any other strong acid is equal to the negative logarithm base 10 of the hydrogen ion concentration (H+).
pH = -log[H+]
pH = -log(0.1)
pH ≈ 1 (approximately)
Therefore, the initial pH of the 100 mM Tris HCl solution is approximately 1.
Moving to the second part of your question,
Robin adds 100 ul (microliters) of 50% NaOH to the solution.
Here's how you can calculate the new pH:
1. Determine the moles of NaOH added:
Since volume is in microliters and concentration is given as a percentage, convert the volume to liters and calculate the moles of NaOH added.
100 ul = 100 × 10^-6 L
Moles of NaOH added = volume × concentration
= 100 × 10^-6 L × 50% = 50 × 10^-6 moles
2. Determine the new total volume of the solution:
100 mL (initial volume) + 100 ul (added volume) = 100.1 mL or 0.1001 L
3. Determine the new concentration of NaOH in the solution:
Moles of NaOH in the solution = 50 × 10^-6 moles
Concentration of NaOH in the solution = moles/volume
= 50 × 10^-6 moles / 0.1001 L
4. NaOH is a strong base, so it will dissociate completely in water. The hydroxide ions (OH-) will react with the hydrogen ions (H+) in the solution, resulting in a change in pH.
To calculate the new pH, you will need to determine the new concentration of hydrogen ions after the reaction with the hydroxide ions.
Subtract the moles of OH- from the moles of H+ initially present in the solution (from Tris HCl), and then calculate the new concentration of H+ in moles per liter (M).
5. Finally, calculate the new pH using the formula:
pH = -log[H+]
Using these steps, you can determine the new pH of the solution after adding NaOH (50% NaOH in this case).