what is the molarity of a solution made by dissolving 188g of MgCl2 in 500g of water?

Answer 1

This question actually can't be answered unless you know the density of the final solution or you assume the volume of the solution is the volume of the water (dilute solution) - not likely in this case.

The molarity would be the moles of MgCl₂/ volume of solution in liters.

The moles of MgCl₂ = mass of MgCl₂/molar mass of MgCl₂

The liters of solution = (mass of MgCl₂ + 500 g Water)/ density of the solution in g/liter

The formula is (m_i/M_i)/((m_i+m_w)/(1000ρ_soln)) where density is the more typical g/ml

molality would be more straight forward: divide mole MgCl₂/.5 liters of water. (.5 liter = .5 kg = 500g)