56mL of a stock solution of hydrobromic acid, HBr, is added to 85mL of water, yielding a solution having a pH of 1.0. What was the molarity of the stock solution?
I know Molarity = moles of solute/ liters of solution
pH = 1.0; (H^+) = 0.1
So you added 56 mL of ?M to 85 mL H2O and the result was 0.1M.
?M x (56/(56+85) = 0.1
Solve for ?M
This assumes, of course, that the volumes are additive. Technically they are not but is dilutions that is usually considered to be so.
Or if you want to do it by mols, you can.
volume = 85 + 56 = 141 mL = 0.141 L
mols in final solution = M x L
That many mols will be in the 56 mL; therefore, that many mols/0.056 = ?M
You shuld get the same answer either way.
To find the molarity of the stock solution, we first need to determine the moles of solute (hydrobromic acid, HBr) and the volume of the solution.
We are given the volume of the stock solution (56 mL) and the volume of water (85 mL) added to it. To find the total volume of the solution, we add these two volumes together:
Total volume of solution = volume of stock solution + volume of water
= 56 mL + 85 mL
= 141 mL
Now, we need to convert the total volume of the solution to liters:
Total volume of solution in liters = (total volume of solution in mL) / 1000 mL/L
= 141 mL / 1000 mL/L
= 0.141 L
Next, we need to calculate the moles of HBr present in the stock solution. For any acid, the concentration is given in terms of moles per liter, so we need to use the molarity formula. Rearranging it, we have:
Moles of solute (HBr) = Molarity × volume of solution (in liters)
Since we are trying to find the molarity (M), we rearrange the formula again:
Molarity (M) = Moles of solute (HBr) / Volume of solution (in liters)
Given that the solution has a pH of 1.0, we know that the concentration of H+ ions is 10^-1 M. Since HBr is a strong acid, it fully dissociates in water, and we can assume the concentration of HBr is the same as the concentration of H+ ions. Therefore, we can use this concentration to find moles of HBr.
Moles of solute (HBr) = Concentration (M) × volume of solution (in liters)
= 10^-1 M × 0.141 L
= 0.0141 moles of HBr
Now, we can substitute the values into the molarity equation to find the molarity of the stock solution:
Molarity (M) = Moles of solute (HBr) / Volume of solution (in liters)
= 0.0141 moles / 0.141 L
= 0.10 M
Therefore, the molarity of the stock solution of hydrobromic acid (HBr) is 0.10 M.