In a concentration calculation, if we are given the moles of solute and the grams of solvent, what do we need to do first in order to find the molality?

Amount of solute/ mass of solvent in kilogrammes

Explanation:

The molality is defined as amount of solute divided by mass of solvent in kilogrammes. Hence first convert the mass of solvent to kilogrammes and the divide the given amount of solute in moles by this mass of solvent in kilogrammes. This gives us the molality of the solution

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g

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