"Moles" is a unit of measurement used in chemistry to quantify the amount of a substance. In this case, "moles of OH-" refers to the number of molecules or ions of the hydroxide ion (OH-) present in a given sample.
To calculate the number of moles of OH- in a solution, you need to know the concentration of the solution (in moles per liter) and the volume of the solution (in liters). You can then use the formula: moles = concentration (in mol/L) x volume (in L).
The concentration of the solution is given as 0.005 M, which means there are 0.005 moles of Ba(OH)- ions per liter of solution.
Molarity is a measure of the concentration of a solution and is calculated by dividing the number of moles of solute by the volume of the solution in liters. In this example, the molarity would be 0.005 moles / 0.3 L = 0.0167 M.
The number of moles of OH- in a solution can give us information about the chemical properties and reactivity of the solution. It can also be used to determine the amount of other substances present in the solution through stoichiometric calculations.