How would you do this question:

A student dissolved 5.0 g of vitamin C in
250 mL of water. The molar mass of ascorbic acid is 176 g/mol, and its Ka is 8.0 × 10−5. Calculate the pH of the solution. Note: Abbreviate the formula of ascorbic acid to HAsc.

mols HAsc = 5/molar mass = approx 0.03 but you need to do it more accurately.

........HAsc ==> H^+ + Asc^-
I......0.03......0......0
C.......-x.......x.......x
E......0.03-x....x......x

Substitute the E line into Ka expression for HAsc and solve for x, then convert to pH.

To calculate the pH of the solution, we need to determine the concentration of H+ ions in the solution. We can do this by first finding the concentration of ascorbic acid (HAsc) using the given mass and molar mass, and then considering its dissociation in water.

Here's how you can solve this question step-by-step:

Step 1: Calculate the moles of ascorbic acid (HAsc)
Moles of HAsc = Mass of HAsc / Molar mass of HAsc

Given: Mass of HAsc = 5.0 g
Molar mass of HAsc = 176 g/mol

Substituting the values:
Moles of HAsc = 5.0 g / 176 g/mol

Step 2: Calculate the concentration of ascorbic acid (HAsc)
Concentration of HAsc = Moles of HAsc / Volume of solution

Given: Volume of solution = 250 mL = 0.250 L

Substituting the values:
Concentration of HAsc = (5.0 g / 176 g/mol) / 0.250 L

Step 3: Determine the concentration of H+ ions
Since ascorbic acid is a weak acid, it partially dissociates in water. The dissociation reaction can be written as follows:

HAsc (ascorbic acid) ⇌ H+ (aq) + Asc- (ascorbate ion)

The Ka value given (8.0 × 10^-5) represents the acid dissociation constant, which is the ratio of the concentrations of the products (H+ and Asc-) to the concentration of the reactant (HAsc). We can assume that the concentration of H+ ions formed is equal to the concentration of the dissociated HAsc.

Therefore, [H+] = [HAsc]

Step 4: Calculate the concentration of H+ ions (acidic concentration)
[H+] = Concentration of HAsc

Step 5: Calculate the pH of the solution
The pH is the negative logarithm (base 10) of the concentration of H+ ions:

pH = -log10([H+])

Substitute the value of [H+] into the equation and calculate the pH.

And that's how you would answer the question to calculate the pH of the solution.