I need to find the pH of a 500 mL solution of pure water after adding 33.0 mg of H2SO4 and 18.0 mg of HCl. Please help! So far I have tried to find the moles of 33.0mg of H2SO4 and got 3.24. Then I calculated pH by multiplying the subscript of H (2) by the moles (3.24) and then took the negative log (-0.8). Do I do the same for HCl...and then what?
To find the pH of the solution, you need to consider the dissociation of both H2SO4 and HCl in water. Here's how you can proceed:
1. Start by calculating the moles of H2SO4 and HCl that you added to the solution. You mentioned that you found 3.24 moles for the 33.0 mg of H2SO4. However, that seems incorrect. To calculate moles, you need to divide the mass of the substance by its molar mass. The molar masses of H2SO4 and HCl are approximately 98.09 g/mol and 36.46 g/mol, respectively. So, the correct calculations would be:
- Moles of H2SO4 = mass (33.0 mg) / molar mass (98.09 g/mol) = 0.336 moles
- Moles of HCl = mass (18.0 mg) / molar mass (36.46 g/mol) = 0.493 moles
2. Both H2SO4 and HCl are strong acids, which means they dissociate completely in water. H2SO4 will release 2 moles of H+ ions per mole, while HCl will release 1 mole of H+ ions per mole.
3. Calculate the total moles of H+ ions in the solution:
- Total moles of H+ ions = (2 moles H+ per mole of H2SO4) * (0.336 moles of H2SO4) +
(1 mole H+ per mole of HCl) * (0.493 moles of HCl)
4. Next, calculate the molarity (M) of the solution. Molarity is defined as moles of solute divided by the volume of the solution in liters. In this case, the volume of the solution is 500 mL, which is 0.5 L.
- Molarity (H+) = Total moles of H+ ions (from step 3) / Volume of the solution (0.5 L)
5. Finally, calculate the pH of the solution by taking the negative logarithm (base 10) of the H+ ion concentration:
- pH = -log10 (Molarity (H+))
Repeat steps 4 and 5 for each of H2SO4 and HCl, and then take the average of the resulting pH values to find the pH of the solution after adding both acids.
Note: It's worth mentioning that when acids are added to water, the water itself can also contribute to the H+ ion concentration and affect the pH. In this case, since you started with pure water, the contribution of water to the H+ ion concentration will be negligible. However, in more complex scenarios, the pH calculation might involve additional considerations.