Step by step chemistry

Question

What would be the concentration of hydroxide ions in a solution made by dissolving 10.0 g of sodium hydroxide in a solution with a final volume of 150.0 mL

Answer 1

The question provides you with the mass of NaOH (10g) and the volume of the final solution (150mL or 0.150L).

So... to find the concentration of hydroxide ions we must first find the moles of hydroxide ions that dissociate in the solution. In order to do this, we can use the chemical reaction:

NaOH ----> Na⁺ + OH^-

This reaction tells us that for every 1 mole of NaOH we will get 1 mole of hydroxide ions.

So... we must take the mass of NaOH (given) and divide by the molar mass of NaOH (40g/mol).

10g x (1mol NaOH / 40 g) = 0.25 mol of NaOH.

Now we multiply by the molar ratio given by the chemical reaction between NaOH and OH^-, which is simply 1 to 1. So in other words, for every 1 mole of NaOH we will produce 1 mole of OH^-.

So.... we take the 0.25 mol of NaOH and multiply it by our molar ration of 1:1.

0.25 mol NaOH x (1 mol OH^- / 1 mol NaOH) = 0.25 mol of OH^-

Now that we have our moles of hydroxide ions, in order to determine the concentration in molarities we must divide by the final volume of our solution (0.150L). This is because concentration in molarity is equal to the moles of solute over the liters of solvent.

So.... we take our 0.25 mol of OH^- and divide by 0.150L

0.25 mol of OH^- / 0.150 L = 1.67 M

1.67 M is the concentration of hydroxide ions in the solution.