Household bleach is a 5.0 mass % aqueous solution of sodium hypochlorite, NaOCl. What is the mol

Household bleach is a 5.0 mass % aqueous solution of sodium...

Key Concepts

Mass Percent

Mass percent is a way to describe the concentration of a solution by expressing the mass of the solute as a percentage of the total mass of the solution. This concept is essential for converting a given percentage into actual masses for the solute and solvent, forming the basis for further concentration calculations.

Molality

Molality is a concentration unit defined as the number of moles of solute per kilogram of solvent. It is particularly useful in scenarios where temperature changes are involved, as it remains independent of temperature and volume variations, providing a reliable measure for the amount of dissolved substance.

Mole Fraction

Mole fraction is a dimensionless measure that expresses the ratio of the number of moles of one component to the total number of moles of all components in a mixture. This concept is important for understanding the composition of solutions, as it provides insights into the relative amounts of substances present without relying on mass or volume units.

Transcript

00:01 All right, so here we've been given an initial concentration in terms of mass percent.

00:06 And what this can be interpreted as is that you'll have five grams of our active ingredient, sodium hypochloride, per 100 grams of the total solution.

00:19 And so what we've been asked to do is to take that starting concentration and express it in both molality and then as mole fractions.

00:29 Or the mole fraction specifically of n .a .o .c .l.

00:35 All right.

00:36 So let's go ahead and get started with the molality portion.

00:39 So molality is defined as the moles of solute, naocl in this case, per kilograms of solvent.

00:49 Now our moles of naocl can be obtained by using the molar mass to convert from grams to moles.

00:56 So let's go ahead and do that portion.

00:58 So five grams of neocl.

01:00 We can set up one conversion factor to go from grams to moles.

01:06 And what we'll do is we'll look at the periodic table and we'll add up sodium, which is 22 .99 grams per mole plus oxygen, 16 plus chlorine, 35 .45.

01:18 And that tells us that this has a mass of 74 .44 grams for one mole.

01:23 5 divided by that number tells us that total we have 0 .067 moles of our solute sodium hypochloride.

01:35 Now, for the kilograms of solvent, what we have to realize is that the 100 grams of solution from our original mass percent is a combination of the grams of water plus the grams of our sodium.

01:53 Hypochloride...

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