Concentrated aqueous ammonia has a molarity of 14.8 and a density of 0.90 g / cm^3 . What is the

Concentrated aqueous ammonia has a molarity of 14.8 and a...

Key Concepts

Molarity

Molarity is a concentration unit defined as the number of moles of solute per liter of solution. It is widely used in chemistry to describe the concentration of solutions and is essential when preparing or diluting reagents, especially in reactions where precise stoichiometry is necessary.

Density

Density is the mass per unit volume of a substance, typically expressed in grams per cubic centimeter (g/cm³) for liquids. In solution chemistry, density is used to convert between the volume of a solution and its mass, which is crucial when changing from concentration units based on volume (like molarity) to those based on mass (like molality or weight percent).

Molality

Molality is a concentration unit defined as the number of moles of solute per kilogram of solvent. Unlike molarity, which depends on the volume of the solution, molality depends solely on the mass of the solvent, making it particularly useful for temperature-dependent studies as mass does not change with temperature.

Mole Fraction

Mole fraction represents the ratio of the number of moles of a component to the total number of moles of all components in a mixture. It is a dimensionless quantity that provides insight into the composition of a solution on a molecular basis and is useful in understanding colligative properties and partial pressures in gaseous mixtures.

Weight Percent

Weight percent (often abbreviated as wt%) is a measure of concentration expressed as the mass of solute divided by the total mass of the solution, multiplied by 100. It is used to describe the composition of mixtures and solutions by mass, making it practical for characterizing solution concentrations, particularly in industrial and laboratory settings.

Transcript

00:01 In this problem, you have an aqueous solution of ammonia with a molarity of 14 .8 and a density of 0 .9 grams per cubic centimeter.

00:21 The problem asks you to determine the molality, mole fraction, and weight percent of the ammonia in solution.

00:41 So let's start by finding the molality.

00:44 The molality of nh3 is defined as the moles of solute, which is ammonia, over the kilograms of solvent, which is water.

01:12 So we need to find these two different values from the given information.

01:18 So let's start by using the molarity.

01:20 Our molarity is 14 .8, and that is defined as the moles of solute.

01:34 Nh3 over liters of solution.

01:43 This means that for every one liter of solution, we have 14 .8 moles of nh3.

01:57 To make it easy for ourselves, let's assume that we have one liter of solution so that our moles of ammonia is equal to 14 .8.

02:06 So now we know the first value we need the moles of nh3.

02:11 Now we just need to find the kilograms of water.

02:14 This is a bit more complicated.

02:18 We can use the density to find the mass of the solution and find the mass of water from there.

02:25 So we have one liter of solution and that's going to be equal to 1 ,000 milliliters.

02:37 And we can find the mass of this solution by multiplying by the density, which is 0 .9 grams per every 1 milliliter.

02:51 This means that the mass of the whole solution is 900 grams.

02:57 This this 900 grams is equal to the mass of the nh3 plus the mass of water.

03:18 In order to find the mass of water, we have to subtract the mass of nh3 from the 900 grams.

03:25 We have the moles of nh3 and we can convert this to mass by taking the number of moles, 14 .8, and dividing by, or multiplying by the molar mass of ammonia, which is just 17 .031 grams per mole.

03:48 And when we do that, we find that we have 252 grams of ammonia.

03:56 So now we can find the grams of water...

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