Can someone help me in this? Concentrated #HNO_3# has specific gravity of 1.42. It contains 69% w/w (weight by weight) of #HNO_3#. Calculate the molarity and molality of the solution?
1 Answer
Explanation:
A liquid's specific gravity is simply the ratio between its density and the density of a reference liquid, more often than not water, at the same temperature.
Usually, the specific gravity for liquids is given at
So, in other words, using the specific gravity of a concentrated nitric acid solution is simply another way of saying that its density is 1.42 g/mL.
Now for the actual calculations. Select a 1.0-L sample of your stock solution, then use its density to determine what its mass is.
You also know the solution's percent concentration by mass to be 69%. This of cours implies that every 100 g of solution will contain 69 g of nitric acid.
The mass of nitric acid your sample contains will be
Use nitric acid's molar mass to determine the number of moles you have
The solution's molarity, which is defined as the number of moles of solute, in your case nitric acid, divided by the volume of the solution - in liters - will thus be
To get the solution's molality, which is defined s moles of solute per kilograms of solvent, you need to first figure out how much water you have.
Therefore, the molality will be
SIDE NOTE I left the answers rounded to three sig figs.