Determine a pH range for which a buffer system containing benzoic acid would be appropriate. Devise a recipe for preparing 1.0 L of buffer solution that contains a total of 0.150 mol of buffer components (acid plus conjugate base) and has a pH of 4.48. The conjugate base will be added in the form of sodium benzoate.
i dont really know what this problem is asking me to do or how to approach it?
The pH range is pKa for benzoic acid +/- 1 and you will need to look up the pKa for benzoic acid.
Where are you having trouble with the problem. You have two ways to go.
1. Start with benzoic acid and add enough NaOH to get the pH you want, or
2. Start with benzoic acid and add sodium benzoate.
Which is the way you've been doing it.
so i found pH and pKa then set up molbase+molacid=.150
then solved what melbase/molacid is and did simple algebra
i got .099?
OK I don't know what pKa you are using but I obtained 0.0984 for mols base using pKa of 4.20.
mol = grams/molar mass.
You know mols and you know molar mass, solve for grams.
grams = 0.099 x 122 = ?
To determine a pH range for which a buffer system containing benzoic acid would be appropriate, you need to consider the pKa of benzoic acid. The pKa is a measure of the acid's tendency to lose a proton and become its conjugate base.
In this case, benzoic acid (C6H5COOH) dissociates into its conjugate base, called benzoate (C6H5COO-), and a proton (H+). The pKa of benzoic acid is 4.20.
For a buffer solution to function effectively, the pH of the solution should be within approximately ±1 unit of the pKa value. In this case, a suitable pH range for the buffer system containing benzoic acid would be around 3.20 to 5.20.
Now, let's devise a recipe for preparing a 1.0 L buffer solution with a pH of 4.48 and a total of 0.150 mol of buffer components (acid plus conjugate base):
Step 1: Calculate the ratio of benzoic acid to sodium benzoate required to achieve the desired pH.
Since the Henderson-Hasselbalch equation for a buffer system is pH = pKa + log([conjugate base]/[acid]), we can rearrange the equation to solve for the ratio:
[conjugate base]/[acid] = 10^(pH - pKa)
Plugging in the values, [conjugate base]/[acid] = 10^(4.48 - 4.20) = 2.5119.
Step 2: Determine the amount of benzoic acid and sodium benzoate needed.
First, calculate the moles of benzoic acid and sodium benzoate required using the total moles of buffer components:
moles of benzoic acid = [acid] = (0.150 mol) / (1 + 2.5119) = 0.05768 mol
moles of sodium benzoate = [conjugate base] = (0.05768 mol) * 2.5119 = 0.145 mols
Step 3: Calculate the masses of benzoic acid and sodium benzoate.
Using the molar masses of benzoic acid (C6H5COOH) and sodium benzoate (C6H5COONa):
mass of benzoic acid = moles of benzoic acid * molar mass of benzoic acid
mass of sodium benzoate = moles of sodium benzoate * molar mass of sodium benzoate
Step 4: Dissolve and mix the calculated masses of benzoic acid and sodium benzoate in distilled water to make a 1.0 L solution.
Make sure to calculate the volume of water needed accurately, as you need a total volume of 1.0 L.
That's it! You have now prepared a 1.0 L buffer solution that contains a total of 0.150 mol of buffer components and has a pH of 4.48, using benzoic acid and sodium benzoate as the buffer components.