Question
Question: Aqueous solution of NaOH is marked 10% w/w. The density of the solution is \[{\text{1}}{\text{.070 g...
Aqueous solution of NaOH is marked 10% w/w. The density of the solution is 1.070 g/cm3. Calculate
A.Molarity
B.Molality
C.Mole fraction of NaOH in water
[Na=23,H=1,O=16]
Solution
In case a different amount of reactants is given then we will proceed with respect to limiting reagent. Limiting reagent is the reagent which consumes in the reaction completely. We shall calculate the number of moles of NaOH and then use that to calculate the molarity, molality and mole fraction.
Formula used:
Molarity=volume of solution in Lnumber of moles
Molality=mass of solvent in Kgnumber of moles
Mole fraction of component A=total number of molesnumber of moles of A
Complete step by step answer:
In the given question, NaOH is marked as {\text{10% w}}/{\text{w}} which is also known as percentage composition that means 10 g of solute is present in 100 g of solution. Density of the solution is given to us in the question. Hence the volume of the solution will be: 1.070 g/cm3100
The molar mass of sodium hydroxide that is NaOH is 40 g. using the volume of the solution and formula for molarity and number of moles we will get:
Molarity =40×10010×1.070×1000=2.14 M
We have used 1000 to convert mL into L.
For calculation of molarity we need the mass of the solvent.
Mass of solvent = Mass of solution − Mass of solvent
⇒Mass of solvent=100−10=90g
Using the formula we will get:
Molality =40×9010×1000=2.2 m
There are two components that are water and sodium hydroxides. Mass and molar mass of both of them is known to us hence the mole fraction of sodium hydroxide using the formula will be:
Mole fraction=0.25+10900.25
⇒Mole fraction=5.250.25=0.9
The number of moles of sodium hydroxide was calculated already and the molar mass of water is 18.
Note:
Sodium hydroxide is also known as caustic soda. It is very much soluble in water. It readily absorbs water from the air. Whenever they are left open in air they absorb water and sticks to each other. It is a strong base and undergoes complete neutralization in the presence of strong acid forming salt and water. It is used in pH regulation, to synthesise the sodium salt, in making soaps and detergents.