0.0100 Ba(OH)2 is dissolved in water to give 500.0 mL of solution
calculate OH- concentration
would it be the molarity of Ba(OH)2 (0.0100 / 0.500) multiplied by two because there is twice as much OH??
Yes.
Yes, you are correct. To calculate the OH- concentration in the solution, you need to consider the dissociation of Ba(OH)2. Ba(OH)2 dissociates into one Ba2+ ion and two OH- ions.
First, calculate the molarity of Ba(OH)2:
Molarity = moles of solute / volume of solution (in liters)
Molarity = 0.0100 moles / 0.500 L = 0.020 M
Since there are two OH- ions for each Ba(OH)2 molecule, the concentration of OH- ions will be twice the molarity of Ba(OH)2.
OH- concentration = 2 * (0.020 M) = 0.040 M
Therefore, the concentration of OH- ions in the solution is 0.040 M.