Final answer:
To obtain a solution with a pH of 1.20, 1.6146 grams of HI are required in 0.200 L of solution. The provided answer options do not match the calculated mass.
Step-by-step explanation:
To determine what mass of HI is needed to obtain a solution with a pH of 1.20 in 0.200 L of solution, we must first convert the pH into hydrogen ion concentration [H+], use the concentration to find the number of moles of HI, and then calculate the mass from the moles.
pH is related to hydrogen ion concentration by the formula:
pH = -log[H+]
By inversely calculating the hydrogen ion concentration from the given pH, we have:
[H+] = 10-pH = 10-1.20 = 0.0631 M
Now, we can find the moles of HI in 0.200 L of solution:
moles HI = volume (L) × molarity (M) = 0.200 L × 0.0631 M = 0.01262 moles
Hydroiodic acid (HI) has a molar mass of approximately 127.91 g/mol, thus:
mass HI = moles × molar mass = 0.01262 moles × 127.91 g/mol = 1.6146 g
None of the given mass options (a) 0.010 g, (b) 0.025 g, (c) 0.050 g, or (d) 0.100 g correspond to the calculated mass of 1.6146 g necessary for a pH of 1.20.