How To Calculate Normality & Equivalent Weight For Acid Base Reactions In Chemistry

In this video we are going to talk about how to

calculate

normality

in relation to

acid

s and

base

s. Now the first thing we're going to talk about is how to

calculate

normality

if you're given the molarity of a solution and then we'll talk about how to calculate it using

equivalent

weight

s, so the formula you need to know is this equation: Normality is molarity multiplied by n, where n is the number of protons per formula unit in the case of

acid

s or hydroxide ions per formula unit in the case of acids. case of

base

s, so I'm going to give you four practice problems, the first will be 0.15 molar of hcl, 1.4 m of sulfuric acid, 2 molar of sodium hydroxide, 0.4 m of barium hydroxide and that That's all, so let's start with the first one to check normality. will be the concentration which is point 15 and this is a monoprotic acid there is only one hydrogen per formula unit so n is one so it will be point 15 n so that is the normality for the first solution , as you can see, that's actually not the case.

So bad, now let's move on to the second example, so the concentration is 1.4, but notice that this time we have two hydrogen atoms per unit, so n is 2 1.4 times 2 is 2.8 and that is the normality for this particular example now for the The third example will be 2 times n, in this case there is only one hydroxide ion per formula unit so n is 1 so it will be 2 m and now let's move on to the last example , so the concentration is 0.4 and there are two hydroxide ions. per unit, so 0.4 times 2 is 0.8 and this is how you can calculate the normality of a solution if you are given the molarity using this formula, let's try this problem, what is the normality of a solution that contains 50 grams of sulfuric? acid dissolved in 15 liters, so we will do this in two ways: we will find the molarity and then we will find the normality and then we will use the second method to find the normality directly without using the molarity, so first calculate the molarity the molarity of a solution is defined as moles of solution divided by liters of solution, so I'm going to start with 50 grams of sulfuric acid, so sulfuric acid is the solute, now we assume it's dissolved in 15 liters. of solution and let's say water is the solvent, the first thing we need to do is convert grams to moles, so let's calculate the molar mass of sulfuric acid, the atomic mass of hydrogen is approximately 1.008, sulfur is 32.06 and oxygen is 16. so the molar mass of h2so4 is 98.076, so one mole of h2so4 has a mass of 98.076 grams, so the unit grams cancel out, so we have moles of solution on top.

Now we have to divide it by the liters of the solution, so we have 15 liters of solution. will give us the molarity in moles divided by liters, so it's 50 divided by 98.076 divided by 15. so it will be 0.034 m, so now we can calculate normality using this equation, it's molarity multiplied by n, so molarity is the zero point. three four and there are two hydrogen atoms per formula unit, so this will result in point zero six eight, so that's the normality of the solution, so that's one way you can find it. Now let's talk about the other method we could.

Use it and it's up to you to choose which method works best for you, but I think it's best to have it both ways. Now we must understand that normality is defined as the number of

equivalent

s per liter of solution. Now the definition may vary. Depending on the situation, for acids and bases the normality is equal to the equivalent

weight

or the number of equivalent weights divided by the liters of solution. So how can we determine the number of equivalent weights? How can we calculate it so that it is an equivalent weight? equal to the mass produced by one mole of protons for acids and for bases would be one mole of hydroxy ions.

I'm going to focus on the definition of acids, so that's an equivalent weight. Now it is the mass that produces one mole of h plus ions. This is the process you want to follow, step one, the first thing you need to do is start with one mole of h plus and convert it to grams of substance, this will give you the amount of equivalent weights, this is how you will be able to find it, step two keep in mind Note that an equivalent weight is the mass that one mole of h produces, also that's where you want to start with one mole of h and now in step two, take the grams of substance and then convert them to the number of, you can convert it directly to the normality, where normality is the equivalent weight per liter.

I guess once you finish step one, you can go straight to step two and just convert it back to normal, so I'll go ahead and show you how to do it all in one step, our ultimate goal. is to get the equivalent weight per liter so let's start with one mole of h and now one mole of sulfuric acid contains two moles of h plus so always keep track of the units so now that we have moles of h2so4 let's convert it to grams. I know the molar mass is 98.076 grams of sulfuric acid per 1 mole of h2so4 instead of doing it all at once, I'm just going to divide it into two parts, I think it's better this way, so 98.076 divided by 2, so this It's 49 grams, so you need to know what that means.

This is the equivalent mass, which is basically the equivalent weight, but this is what you want to take from the first step: write down a conversion factor and that's an equivalent weight that's equal to 49.038 grams. so now we have the equivalent weight, now we need to calculate the normality, so the normality is the number of equivalent weights divided by the liters. Note that this correlates to an equivalent weight, so 50 grams is a little more than an equivalent weight. What you want to do now is start with the original mass that you have because that number can vary, so we'll start with 50 grams of sulfuric acid and then we'll convert grams to the number of equivalent weights, so an equivalent weight is 49.03 grams. so the unit of grams cancels out and then once you have the number of equivalent weights that is just above one, it's 50 divided by 49,038, take that result and divide it by the volume of the solution in liters, so that Let it be 50 divided by 49,038, so it is 1.0196 equivalent pesos. divided by 15, then this will be point zero six seven nine seven, which is rounded to point zero six eight n or equivalent normality weights per liter, this is how you can calculate the normality of a solution.

Now let's try a second example problem so that you can understand this topic and I think it is better if you pause the video and follow the steps of the last problem to see if you can get the answer in this problem. I would recommend doing it both ways so you can understand how to calculate normality. In other situations, when dealing with acid-base

reactions

, let's first calculate the molarity of the solution, so let's start with the mass of 1.5 grams of calcium hydroxide and then convert it to moles so that we have one calcium atom, two oxygen atoms and two hydrogen atoms. so the atomic mass of calcium is 40.08, let me confirm the periodic table and yes, that is correct and oxygen is 16.

Hydrogen is 1.008, so the molar mass is 74.096 grams per 1 mole. Now that we have the moles of calcium hydroxide that we need. divide it by the liters of solution now we have 850 milliliters which is the same as 0.85 liters to convert milliliters to liters divide by a thousand keep in mind that a liter is a thousand milliliters so now we have moles divided by liters and that will give us the molarity of the solution then it is 1.5 divided by 74.096 divided by 0.85 so the molarity is 0.0238 m now that we have the molarity we can calculate the normality using this equation molarity multiplied by n so the molarity is 0.0238 now what is n in this problem calcium ?

Hydroxide has two hydroxide ions per formula unit, so n is two, so the normality that I'm going to write at the top is point zero four seven six n, so that's the normality of the solution , let's see if we can get the same answer using the second method, so make sure you try that first before looking at the solution, so let's start with one mole of h plus now one mole of h plus reacts equivalently, excuse me, so equivalent with one mole of hydroxide, so if you started with one mole of h plus or one mole of hydroxide you can still get the correct answer.

I just have a habit of starting with one mole of h plus. Now one mole of calcium hydroxide contains two moles of hydroxide ions, so now we can cancel these units and now let's convert. moles to grams using the molar mass and the molar mass of calcium hydroxide is 74.096 grams times 1 mole, so this will be 1 multiplied by 74.096 divided by 2, so this is equal to 37.048 grams, so this is equal to the equivalent weight, so one The equivalent weight is 37.048 grams, that's our conversion factor. Now that we have the conversion between equivalent weights and grams for this substance, we can now calculate the normality of the solution.

Now, for the second part, let's start with the mass of the substance, the mass that is given to it. So we have 1.5 grams of calcium hydroxide. Then, using this conversion factor, convert it to the number of equivalent weights, so that an equivalent weight is 37.048 grams. Now that you have the number of equivalent weights divided by the liters of solution, then 850 milliliters, like we said. before is 0.85 liters, so remember that normal is the number of equivalent weights divided by liters of solution, so make sure you end up with those two equivalent weight units on top and liters in the denominator of the fraction , so it will be 1.5 divided by 37.048. which tells us that we have a number of equivalent weights of 0.0405 and then we divide it by 0.85 liters and we get the same answer which is 0.0476 n, so now we have two ways to calculate the normality of the solution , so I hope you found this.

The video will be useful and thanks for watching.