Hey, you guys, this is Mr. millings and today, we're going to continue our discussion of solutions. And today, we're going to learn a little about how to calculate this the composition of a solution using something called mass percent. Okay. So today, we're going to learn a little about something called mass percent. And what is mass percent? Well, it says, right here to get the mass percent of a solution that is to figure out how much solute is dissolved in a solution.

It's simple. We take the mass. Of the solute, the mass of the stuff that's dissolved in the solution, and we're going to divide that by the mass of the entire solution. Now, keep in mind that a solution consists of two parts, the solute, plus the solvent.

So we add these two things together to get the mass of the entire solution. And once we do that, we multiply by a hundred percent. So quite simply to get the mass percent it's simple. We take the mass of the solute divided by the mass of the entire solution, and then we're going to. Multiply by 100 so let's, suppose we have 15 grams of NaCl right here. And we have a hundred grams of water or 100 milliliters of water right here.

And you know that 100 milliliters of water is equal to 100 grams of water because the density of water from an earlier video, we learned is 1 gram per milliliter. Okay. So 100 milliliters of water is going to have a mass of 100 grams. And so what we're going to do with these 15 grams of salt is we're going to scoop some ore we're going to scoop the entire.

Thing into this beaker of water, we're going to stir it up. And now we have a solution of salt water. And so what we want to figure out is the mass percent. We want to know the mass percent of the salt that has been dissolved in this water right here.

Well to get the mass percent. It's simple. We take the mass of the solute, which is 15 grams, and we're going to divide this by we're going to divide this by the mass of the entire solution, right? The mass of the entire solution. Now, the mass of the solution. Is not a hundred grams.

This is the mass of the water. Remember, the mass of the solution is the water plus the salt here right? So 100, plus 15 is 115 and just for SigFig purposes. We're just going to go to make this a decimal right here. And this is decimal 2.

So we have 115 grams of solution, and then we're going to simply multiply by 100%. And so the mass percent of the salt that is in this solution is going to be. It looks like thirteen point. Zero percent actually it's just going to be 13%. If we use. The correct number of SIG figs here, let me get rid of this decimal here. We have two SIG figs here.

We have three SIG figs here. So it looks like it's just going to be 13%. We use the correct number of SIG figs the mass percent of the salt that is in this solution is going to end up being 13%. So we have a 13 percent by mass saltwater solution. Okay. So let's work, a few more examples up and apply the formula for mass percent to several examples. All right so we're when working with the.

Mass percent formula, here's, the main formula mass percent equals mass of solute over mass of solution times 100. But what we can do is we can manipulate this formula around to solve for the mass of this solute. If you want to solve for the mass of the solute it's simple, all we need to do is take the mass of the solution. And the one hundred percent here and put it on the other side of this equation. And the way that we do that is by taking this and putting it up here on the other side and taking. This and put it putting it on the bottom over here on the other side. And what we end up with is this formula right here to get the mass of the solute it's mass of solution times mass percent, divided by 100 percent.

Well, what if you're asked to figure out the mass of the solution? Well, that's simple to figure this one out. We take this. We put it on top over here, and we'll take this, and we'll, put it on the bottom over here. And what we end up with is this formula right here. So the mass percent formula. We can actually break down to three different formulas and solve problems where we're asked to figure out mass percent mass of solute or massive solution.

So let's apply these three formulas to three different example, problems. Okay. In this first example, it says, the solution is prepared by mixing. Twenty-five point five grams of salt with a hundred and fifty grams of water, calculate the mass percent of salt in the salt water solution. So to get the mass percent. We take the mass of the solute divided. By the mass of the solution, so how much stuff is being dissolved?

Well, let's take a look at this word problem. A solution is prepared by mixing twenty-five and a half grams of salt. It looks like the salt is the substance that is being dissolved. So the mass of the solute is right here.

We have. Twenty-five point, five grams of salt that's, the mass of the solute let's read on we're, mixing this salt with a hundred and fifty grams of water. So the solvent has a mass of 150 grams. So what do you think the. Mass of the entire solution is going to be well, if we add this to this, we should end up with one hundred, and seventy-five point five grams as the mass of the solution.

And last we just multiplied by one hundred percent. So to get the mass percent here, you take the mass of the solute, which is twenty-five point, five grams, and then we're going to divide this by the mass of the solution. Remember, the solution always contains two parts to solute, plus the solvent right?

So we have to add these two. Together and we'll end up with one hundred, and seventy-five point five grams times, 100 percent we'll put this in the calculator, and it looks like we'll end up with if we use the correct number of SIG, figs 14.5%, okay. So it looks like here. We have got a 14.5 percents of sodium chloride solution by max all right. Let's. Take a look at another problem.

Alright? And this issue here, it says, cows milk contains 4.5% lactose, which is a sugar. Okay? So cow's milk contains four to five percent. This of this. Sugar by mass, we have to calculate the mass of the lactose present in 175 grams of milk. So we have some milk here, let's draw this out right and this is the milk here.

It says here has a mass of 175 grams. Meanwhile, we know that 4.5 percent of this milk by mass is lactose, right? So 4.5 percent by mass is lactose.

And we have to calculate. We want to know how many grams of lactose there are in this milk, so we're, trying to figure out the mass of the solute. We want to know the mass of the lactose that has.

Been dissolved in this milk here, right? So how do we figure this out? Well, we know the mass percent here. So we know the mass percent is 4.5%. We know the mass of the entire solution is 175. So we can just plug those values into this formula to figure out the number of grams of lactose that are dissolved in this milk here. So to get the mass of the salt solute.

In this case, the lactose you're going to take the mass of the solution, 175 grams, the mass percent, which is 4.5%, and then we're going to. Divide this by 100%. And so when we put this in our calculator, we'll end up with let's see here, 7.9, it looks like we use the correct number of SIG figs. We have 7.9 grams of lactose that has been dissolved in this cow's milk and 175 grams of cow's milk. Okay. So that's how we figure out the mass of the solute let's.

Take a look at one more problem. Okay, in this last example, it says, if 75 grams of sodium nitrate is dissolved to make a 15% solution of sodium nitrate and determine the mass of the. Solution so now we're asked to figure out the mass of the solution, the way we do that is to take the mass of the solute, which it says, right here is 75 point. Zero grams of this stuff right here that is being dissolved so that's, the mass of the solute right here, we're then going to multiply by a hundred percent, and then we're going to divide by the mass percent of the solution, which it says, right here is a fifteen percent solution.

Okay. So let's do that to get the mass of the solution you're. Going to take the mass of the solute, the stuff being dissolved 75.0 grams, which has three significant figures times 100%, and then we're going to divide this by the mass percent, which is 15%.

And when we put this in our calculator, we will end up with looks like 500 this cancels out the % cancels out leaving us with grams. Alright. Now, keep in mind this here has three significant figures.

So we should be using three SIG figs here. And in order to do that, we have to put a decimal in that number right. There, and so it looks like the mass of the solution is going to be 500 grams. Alright, so that is how we calculate the mass percent of a solution. If you like, what you see, go ahead and click that little bomb in the bottom right-hand corner here, and that will subscribe you and I hope.

This was helpful.