What is the pH change of a 0.220M solution of citric acid (pKa=4.77) if citrate is added to a concentration of 0.155M with no change in volume?
pKa = 4.77 is pK2; therefore, I assume you are asking for the change in pH of that solution, not necessarily that of citric acid. Use the HH equation.
I tried the HH equation and got pH=4.92 when I placed the acid on top of the fraction and that was wrong. I got 4.61 when I placed the citrate on top and that was also wrong...
Well, well, well, looks like we've got ourselves a chemistry question!
Now, citric acid is a real prankster when it comes to pH changes. Let's break it down and make it less acidic for you:
The pKa of citric acid is 4.77, which means that at a pH of 4.77, citric acid and its conjugate base, citrate, are present in equal concentrations.
So, when you add citrate to the solution, it's like inviting more of its laid-back buddy to the party. This means the concentration of citrate will increase to 0.155M, while the concentration of citric acid will decrease slightly.
Now, the pH change. Since citric acid is a weak acid, its pH change depends on the ratio of citric acid to citrate. With a higher concentration of citrate, the pH will increase because the solution becomes more basic.
But the question says there's no change in volume, so if you do the math, you'll find the pH change won't be too drastic. The addition of the citrate will make the solution a bit less acidic, but I doubt it will throw any pH clowns off balance.
Just make sure you keep an eye on those partygoers, because you never know when they might start juggling H+ ions while standing on one foot!
To determine the pH change of a solution when citrate is added, we need to calculate the change in concentration of the citric acid and citrate ions, and then use the Henderson-Hasselbalch equation to calculate the pH change.
First, let's calculate the change in concentration of citric acid (C6H8O7) and citrate ions (C6H5O73-) when citrate is added.
The chemical equation for the dissociation of citric acid can be written as follows:
C6H8O7 ⇌ C6H7O72- + H+
From the balanced equation, we can see that for every one molecule of citric acid, one H+ ion and one citrate ion are produced. Therefore, when citrate is added, the concentration of citric acid will decrease by the same amount as the concentration of citrate ions increases.
Given:
Initial concentration of citric acid (C6H8O7) = 0.220 M
Concentration of added citrate ions (C6H5O73-) = 0.155 M
Since there is no change in volume, the change in concentration of citric acid and citrate ions will be equal.
Change in concentration of citric acid = -0.155 M
Change in concentration of citrate ions = +0.155 M
Now, let's use the Henderson-Hasselbalch equation to determine the pH change:
pH = pKa + log([A-]/[HA])
Given:
pKa of citric acid (C6H8O7) = 4.77
Substituting the values into the equation, we have:
pH = 4.77 + log(0.155/0.220)
Using a logarithmic calculator, we can evaluate the logarithm to get the pH change.
Therefore, the pH change of the 0.220 M solution of citric acid when 0.155 M of citrate is added can be determined using the Henderson-Hasselbalch equation.