In this video, I want to show you a simplified way to calculate the normality of a solution. Now, I've created another video a few years ago with these exact problems in this video, so you could see how it's done with another method, a longer method. But in this video, I'm going to give you a formula where you can go... directly to the answer.
So here it is. The normality is equal to the mass of the solute in grams times n. N is basically the number of H plus ions for acids or hydroxide ions for bases per formula unit. So in the case of H2SO4, in one formula unit, notice we have two hydrogen ions.
Therefore, for this example, N is 2. So N is associated with the acidity or the basicity of the substance, specifically the number of protons or hydroxide ions per formal unit. Now this is going to be divided by V, which is the volume of the solution in liters, multiplied by the molecular weight or the molar mass of the solute. Now, later in this video, I'm going to explain how we can derive that formula. But for now, let's put it to use.
So let's calculate the molecular weight first. So for H2SO4, we have two hydrogen atoms, one sulfur atom, and we have four oxygen atoms. So the atomic mass for hydrogen is 1.008, for sulfur it's 32.06, and for oxygen it's 16, based on the periodic table. So let's go ahead and plug in these numbers. So the molecular weight or the molar mass of H2SO4 is 98.076 grams per mole.
So first we have M. M is the mass of the solute. The solute is H2SO4.
We're assuming that it's dissolved in water, but... We really don't need that in this problem. But we know the mass is 50 grams, that's M. We've already decided that M is 2. There's 2 protons in this acid per formal unit. Now the volume is already in liters, which is good.
And then times the molar mass, 98.076. So it's 50 times 2, which is 100. 100 divided by 15, that's 6.6 repeating. If we divide that by 98.076, we're going to get the answer, which is... 0.06797.
And of course, you could verify this answer with my older video that I've created. You'll see this exact problem just done in a different way. longer way. But that's how you can calculate the normality of a solution directly by using this particular formula. By the way for those of you who want a list of concentration formulas including normality, molarity, molality, parts per million, parts per billion, mole fraction, and other forms of concentration, mass percent and volume percent, Check out the links in the description section below.
I'm going to post the formula sheet there where you can download it and get access to all the different types of, at least the most common types of, concentration formulas that are out there. Now, let's work on another example. This time we want to calculate the normality of a base instead of an acid. By the way, if you want to see that other video that has these exact problems, but...
uses a different method to get the same solution, I'm going to post a link to that video in the description section below for those of you who want to see it as well. So if you want to see another way of getting this answer. But let's begin with a formula. normality is going to be the mass of the solute times n divided by the volume of the solution in liters times the molecular weight of the solute.
So let's begin. by calculating the molecular weight. So for calcium hydroxide, we have one calcium atom.
We have two hydrogen atoms and two oxygen atoms. So the atomic mass of calcium is 40.08. For hydrogen, we know it's 1.008 and then times two. And for oxygen, it's 16. So let's go ahead and plug this in. So this is going to be 74.096 grams per mole.
So the mass of solute is 1.5 grams. Notice how many hydroxide ions we have per formula unit. There's two of them. So n is going to be 2 in this example.
Now the volume of solution. It's not in liters, it's in milliliters. Now keep in mind, 1 liter is 1000 milliliters. So if you want to convert from milliliters to liters, divide by 1000. But if you want to show your work, you can write it this way.
We can start with what we're given, 850 milliliters, and then use the conversion factor. We know 1 liter is equivalent to 1,000 milliliters. Setting up this way, we can see that the unit milliliters will cancel.
850 divided by 1,000 is 0.85. So that's going to be the volume, 0.85 liters. And the molar mass, which we have here, that's 74.096.
So this gives us a normality of 0.04763. So that's how you can calculate the normality of a solution using this formula. Now let's talk about how we can derive this formula. Normality is defined as the number of grams equivalent weight of solute, the number of gram equivalent weight of solute. It's a mouthful.
And it's divided by the liters of solution, which I'm going to put v to represent the volume. Now the number of gram equivalent weight of solute, basically the numerator of that fraction, That's equal to the mass of the solute in grams, which I'm just going to write M, divided by the equivalent weight, which I'm going to write EW for that. Now, the equivalent weight is basically the molecular weight, or the molar mass, divided by N.
And you know what N is. N is the number of hydrogen ions or hydroxide ions per formula unit. So let's start with this formula here. I'm going to replace this term with what we have here. So notice that v is on the bottom, and then it's going to be 1 over v times this, which it becomes m over v times ew.
So basically, I just replaced this with M over EW. The V is still on the bottom. Now, let's rewrite this as... m over v times 1 over ew. This expression is equivalent to this expression.
Now if this is ew, 1 over ew is going to be the reciprocal. It's n over the molecular weight. So I can replace this with what we have here. So we have the mass divided by the volume times the molar mass. Actually, no.
I need to use this here. Times n over the molar mass. So that's how you can derive this formula. for normality. So it's equal to the mass of the solute times n divided by the volume, which is the liters of the solution, and also divided by the molecular weight or the molar mass.
But having that formula, it makes the process of calculating the normality so much easier. If you see my older video on normality, you'll see that it's a lot easier just to use that formula. So that's going to be it for this video.
Thanks again for watching, and don't forget to download that formula sheet.