When 250 grams of potassium hydroxide are dissolved in 2500 mls of water. the resulting volume is 2.585 liters of solution. what is the molarity of the solution?

Since the molar mass of KOH is 56.105 g, you have 250/56.105 = 4.456 moles of KOH in 2.585 litres of solution, so the molarity is 4.456/2.585 = 1.724 M. 

If you calculate the number of moles in 2500 mL of water and assume that the density of the solvent, water, is 1 kg/litre you obtain the molality m = 1.782 mol/kg

Determine the  wavelength of light emitted when an electron  in an li2+ ion  makes a transition from an orbital with n  =  6 to an orbital with n  = 5.

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