A solution is prepared by dissolving 28.4 g of glucose (C6 H12 O6) in 355 g of water. The final

A solution is prepared by dissolving 28.4 g of glucose (C6...

Key Concepts

Mole Percent

Mole percent is the mole fraction expressed as a percentage. It quantifies the relative number of moles of a given component compared to the total moles in the mixture, multiplied by 100. This conversion simplifies the understanding of the composition of mixtures for many practical applications in chemistry.

Mole Fraction

Mole fraction is a dimensionless quantity that describes the composition of a solution by dividing the number of moles of a component by the total number of moles of all components in the mixture. This concept is widely used in fields such as thermodynamics and physical chemistry because it does not depend on temperature or pressure.

Molality

Molality is a concentration unit defined as the number of moles of solute per kilogram of solvent. Unlike molarity, molality is based on mass rather than volume, which makes it independent of temperature changes. This property is particularly useful in situations where temperature fluctuations affect the volume, such as in colligative property studies.

Molarity

Molarity is a measure of concentration expressed as the number of moles of solute per liter of solution. It is used to relate the amount of a substance to the total solution volume, and because volume can vary with temperature, molarity is temperature?dependent. This concept is essential in preparing solutions and performing stoichiometric calculations in chemical reactions.

Percent by Mass

Percent by mass, also known as mass percent, represents the ratio of the mass of the solute to the total mass of the solution, expressed as a percentage. This unit is important for expressing the composition of mixtures, especially in contexts where precise mass proportions are critical, such as in industrial formulations or quality control.

Transcript

00:01 So in chemistry, we always kind of let the units lead us solving problems.

00:07 In this case, we're asked to calculate several different ones.

00:14 So the first one's molarity.

00:16 So recall molarity has units of the moles.

00:29 This will be the moles of the solute.

00:40 The liters of this case of the entire solution.

00:49 Alright, so first thing we're going to do is we're given that the solute is 28 .4 the sugar or the glucose.

01:02 It's in grams.

01:05 We need to convert that.

01:06 So if we multiply that against the molecular weight of glucose.

01:12 So one thing we should know is glucose molecular weight.

01:21 They give us the four in the one.

01:22 So we can actually calculate its molecular weight.

01:26 So if you look at a periodic table, we see the carbon has a 1 about 12 grams per mole.

01:35 We'll multiply that by six since glucose has six carbons and that to the molecular weight of hydrogen.

01:46 So there are 12 hydrogens.

01:51 Looking at the molecular table, it's about 1 gram per more plus, and there's six oxygens.

02:03 You can not see what i'm seeing.

02:04 So it's just a c6h12.

02:09 Oh, six.

02:12 That's the multiple formula we're looking at for glucose.

02:19 And then looking at that milk weight of each option is about 16.

02:25 That gets you about 180 grams per one mole.

02:34 Okay.

02:36 So we do, we have to multiply it.

02:39 Well, really we haven't going to divide it because we want to cancel out those grams.

02:43 So we just get the moles.

02:46 So we do that.

02:51 Cancel out units.

02:55 28 .4 times 1 is just 20 .4.

02:59 Divide that by 180.

03:02 Put in a calculator, which you get is about 0 .15.

03:10 There's more of the sevens than what i'm showing here, but i just stop it right here, 1 .5, 7 ,7, 8 moles.

03:19 Then, if we're going to calculate molarity, since we know that solution is about 378 milliliters we convert 3 to 78 milliliters you know there's a thousand mil liters for every one liter and we're just cancel we're setting it up so we can cancel out like units this comes about 0 .378 liters so the final thing for looking for malarity is going to be 0 .15778 moles.

04:09 And we divide that by the 0 .378 liters.

04:18 The result of that's going about 0 .417.

04:25 Seven moles, molar, or molar, okay? because it's a moles per liter.

04:32 And that would be your answer for, in this case, a, he's a little different.

04:40 It's just talking about molality.

04:44 Malality is going to be, instead of being mold of solute over liter solution, is moles still a solute over kilograms or the mass.

05:07 Of the solvent, in which case this is water.

05:13 So we bring this down a little bit...