A chemist dissolves 245.mg of pure hydrochloric acid in enough water to make up 60.mL of solution. Calculate the pH of the solution. Be sure your answer has the correct number of significant digits.
Question
A chemist dissolves 245.mg of pure hydrochloric acid in enough water to make up 60.mL of solution. Calculate the pH of the solution. Be sure your answer has the correct number of significant digits.
Solution
To calculate the pH of the solution, we first need to find the molarity (M) of the solution. Molarity is defined as the number of moles of solute (in this case, hydrochloric acid, HCl) divided by the volume of the solution (in liters).
Step 1: Convert the mass of HCl to moles. The molar mass of HCl is approximately 36.5 g/mol. So,
245 mg = 0.245 g
Number of moles = mass/molar mass = 0.245 g / 36.5 g/mol = 0.00671 mol
Step 2: Convert the volume of the solution to liters.
60 mL = 0.060 L
Step 3: Calculate the molarity of the solution.
Molarity = moles/volume = 0.00671 mol / 0.060 L = 0.112 M
Hydrochloric acid is a strong acid, so it will dissociate completely in water to form H+ and Cl- ions. Therefore, the concentration of H+ ions will be equal to the molarity of the HCl solution.
Step 4: Calculate the pH of the solution. The pH is defined as the negative logarithm (base 10) of the H+ ion concentration.
pH = -log[H+] = -log(0.112) = 0.95
So, the pH of the solution is approximately 0.95. This is a very acidic solution, as expected for a solution of a strong acid like HCl.
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