What is the mass percent concentration of the following...

What is the mass percent concentration of the following solutions? (a) Dissolve 0.655 mol of citric acid, $\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{7},$ in 1.00 $\mathrm{kg}$ of water. (b) Dissolve 0.135 $\mathrm{mg}$ of $\mathrm{KBr}$ in 5.00 $\mathrm{mL}$ of water. (c) Dissolve 5.50 $\mathrm{g}$ of aspirin, $\mathrm{C}_{9} \mathrm{H}_{8} \mathrm{O}_{4},$ in 145 g of dichloromethane, $\mathrm{CH}_{2} \mathrm{Cl}_{2}$

What is the mass percent concentration of the following solutions?
(a) Dissolve 0.655 mol of citric acid, $\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{7},$ in 1.00 $\mathrm{kg}$ of water.
(b) Dissolve 0.135 $\mathrm{mg}$ of $\mathrm{KBr}$ in 5.00 $\mathrm{mL}$ of water.
(c) Dissolve 5.50 $\mathrm{g}$ of aspirin, $\mathrm{C}_{9} \mathrm{H}_{8} \mathrm{O}_{4},$ in 145 g of
dichloromethane, $\mathrm{CH}_{2} \mathrm{Cl}_{2}$

Key Concepts

Mass Percent Concentration

This concept represents the concentration of a solution as the mass of the solute divided by the total mass of the solution, multiplied by 100 to yield a percentage. It provides a measure of how much of the solution's mass is contributed by the dissolved substance, and is especially useful when the volumes of the components may change due to mixing.

Mole-to-Mass Conversion

This concept involves using the molar mass of a substance to convert from moles to grams. It is a fundamental technique in chemistry that allows one to determine the mass of a substance present when the amount in moles is known, which is crucial for preparing solutions and calculating concentrations.

Unit Conversions

Unit conversion is a key skill in solution chemistry which involves converting between different units such as grams, milligrams, and milliliters. This ensures that all values are expressed in compatible units (typically mass units) for accurate calculation of the mass percent concentration.

Total Mass Calculation

This concept involves finding the total mass of a solution by summing the masses of the solute and solvent. Recognizing that the mass percent concentration relies on the combined mass of all components in the solution is essential for accurate concentration calculations.

Transcript

00:01 All right, let's calculate some mass percent compositions.

00:05 So our mass percent is going to be defined as kind of in the simple term, the mass of whatever component we're interested in, which in these cases is going to be the solute, and we're going to divide by the total mass of the solution.

00:22 And then, of course, to convert that to a percent, we'll be multiplying by 100 as the very last part.

00:27 So let's jump in and tackle each part as we come to it.

00:31 So in this case, we have 0 .65 moles of citric acid and one kilogram of water.

00:37 And so since this is mass percent, we're going to need both of those amounts and grams.

00:43 So let's start off with our citric acid here.

00:48 So 0 .655 moles of citric acid.

00:51 That has a formula of c6 h807.

00:54 And just like normal, when we're going from moles to grams, we're going to employ the molar mass from the periodic table, which is where we look at each type of element, hydrogen, carbon, and oxygen, and add up those molar masses.

01:11 So when we do that for our six carbons, eight hydrogens, and seven oxygens, the value that we get is 192 .14 grams.

01:21 We'll multiply that number by our .655.

01:25 And what that gets us is 1206, essentially, grams of our salt ude.

01:35 Now, what we need to also think about is our solvent.

01:39 Our solvent, in this case, is water.

01:42 And it tells us that we have one kilogram of water, which is going to be the same thing as 1 ,000 grams of water.

01:49 So when we're filling in our mass percent formula, on top is going to go the 126 grams of our solute, and on bottom we want the total mass of solution.

02:00 So we'll be adding the 1 ,000 plus the 126, and then at the end we'll be multiplying by 100.

02:08 So 126 divided by 1 ,126, and then finally multiplying by 100 is going to give us a 116.

02:19 Point two mass percent concentration.

02:23 All right, let's go ahead and keep moving on to part b.

02:28 Part b.

02:29 In this case we have 0 .135 milligrams of kbr.

02:35 So again our goal is going to be to convert that to grams.

02:39 This time it's just a metric conversion...