[Edher]

Saludos,

      I'm having trouble understanding this problem:

Calculate [H₃O]  and pH in saturated Ba(OH)₂(aq), which contains 3.9g Ba(OH)₂ * 8H₂O per 100 mL of solution.  

( * means times)

The       * 8H₂O is throwing me off. I don't know how to take it into account in the equation. Also, when finding the molarity of BaOH₂ do I have to add the weight of 8 moles of water to the calculation?

Thank you for your time,
Edher

[plu]

The water molecules there are simply a part of the solid 3.9 grams that you are dissolving into solution (these kinds of solids are referred to as "hydrates").  When you calculate the moles of solid you are dissolving, you must take into account the water molecules as part of the molecular formula.  Other than that, the Ba(OH)₂ is just another base.

[Donaldson Tan]

. which contains 3.9g Ba(OH)₂ * 8H₂O

This is the formula of the salt crystal you used to dissolve. It tells in 1 mole of the crystallised Ba(OH)₂. there is 8 moles of water and 1 mole of Ba(OH)₂. The water in the chemical formula is known as the water of crystallisation.

the molar mass of Ba(OH)₂* 8H₂O
= molar mass of Ba(OH)₂ + 8 x molar mass of water