Question

The concentration of KBr in a solution prepared by dissolving 2.21g of KBr in 897g of water is ______ molala) 2.07 x 10^-5b) 0.0167c) 0.0186d) 0.0207e) 2.46

Answer 1

So, let's first remember that:

The molal concentration, m, is defined as the ratio between moles of solute (In this case, KBr) per kg of solvent (water):

We need to find the moles of solute. For this, we are going to divide the amount of solute given by the problem by the molar mass of KBr.

Now that we found moles of solute, what we need to do is to find the mass of solvent (In this case is water) in Kg. We have 897g so, to pass to Kg what we do is to divide by 1000:

Now, to find molality, we divide the moles of solute and the kilograms of solvent. Therefore, the concentration is:

So the correct answer is D.