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

in this video we're going to talk about how to calculate normality as it relates to acids and bases now the first thing we're going to talk about is how to calculate normality if you're given the molarity of solution and then we'll talk about how to calculate it using equivalent weights so the formula that you need to know is this equation normality is molarity times where is the number of protons per formula unit in the case of acids or hydroxide ions per formula unit in the case of bases so i'm going to give you four practice problems the first one is going to be 0.15 molar hcl 1.4 sulfuric acid 2 molar sodium hydroxide 0.4 barium hydroxide and that's about it so let's start with the first one so the normality is going to be the concentration which is point 15 and this is monoprotic acid there's only one hydrogen per formula unit so is one so it's going to be point 15 so that's the normality for the first solution as you can see it's really not that 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 form unit so is 2 1.4 times 2 is 2.8 and so that's the normality for this particular example now for the third example it's going to be 2 times in this case there's only one hydroxide ion per formula unit so is 1 and so that's going to be 2m and now let's move on to the last example so the concentration is 0.4 and there's two hydroxide ions per form unit so 0.4 times 2 is 0.8 and so that is how you can calculate the normality of solution if you're given the molarity using this formula let's try this problem what is the normality of solution that contains 50 grams of sulfuric acid dissolved in 15 liters so we're going to do this two ways we're going to find the molarity and then find the normality and then we're going to use the second method to find the normality directly without using molarity so first let's calculate the molarity the molarity of solution is defined as the moles of solu divided by the liters of solution so i'm going to start with 50 grams of sulfuric acid so sulfuric acid is the solute now we're assuming it's dissolved in 15 liters of solution and let's say that 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 about 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 mass of 98.076 grams so the unit grams cancel so we have moles of solu on top now we got to divide it by the liters of the solution so we have 15 liters of solution so this is going to give us the molarity moles divided by liters so it's 50 divided by 98.076 divided by 15. so it's going to be .034 so now we can calculate the normality using this equation it's the molarity times so the molarity is point zero three four and there's two hydrogen atoms per formula unit so this is going to work out to be point zero six eight so that's the normality of the solution so that's one way in which you can find it now let's talk about the other method that we could use and it's up to you to pick and choose which method works best for you but think it's best to understand it both ways now we need to understand is that normality is defined as the number of equivalents per liter of solution now the definition can vary based on the situation so 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 figure that out so one equivalent weight is equal to the mass that yields one mole of protons for acids for bases it would be one mole of hydrox ions i'm going to focus on the definition for acids so that's one equivalent weight it's the mass that yields one mole of plus ions now here's the process that you want to follow step one the first thing you want to do is start with one mole of plus and convert it to the grams of substance this will give you the number of equivalent weights that's how you could find it step two keep in mind one equivalent weight is the mass that yields one mole of plus that's where you want to start with one mole of plus now step two take the grams of substance and then just convert it to the number of you can convert it directly to normality where normality is equivalent weight per liter guess once you finish step one you can go directly to step two and just convert it to normality so i'll go ahead and show you how to do it all in one step so our final goal is to get equivalent weight per liter so let's start with one mole of plus now one mole of sulfuric acid contains two moles of plus so always keep track of the units so now that we have moles of h2so4 let's convert it to grams now we know that 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 break it up into two parts think it's best that way so 98.076 divided by 2. so this is 49 grams so you need to know what this means this is the equivalent mass which is basically the equivalent weight but here's what you want to take from the first step you want to write conversion factor and that is one equivalent weight is 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 keep in mind this matches correlates to one equivalent weight so 50 grams is little bit more than one equivalent weight so what you need to do now is start with the original mass that you have because that number can vary so we're going to start with 50 grams of sulfuric acid and then convert grams to the number of equivalent weights so one equivalent weight is 49.03 grams so the unit grams cancel and then once you have the number of equivalent weights which 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 it's 50 divided by 49.038 so that's 1.0196 equivalent weights divided by 15 and so this is going to be point zero six seven nine seven which rounds to point zero six eight or normality equivalent weights per liter so that's how you can calculate the normality of solution now let's try second example problem so that you can understand this topic and think it's best if you pause the video and follow the steps in the last problem to see if you can get the answer in this problem and would recommend doing it both ways so you can understand how to calculate normality in other situations when dealing with acid-base reactions so first let's calculate the molarity of the solution so let's start with the mass 1.5 grams of calcium hydroxide and then let's convert it to moles so we have one calcium atom two oxygen atoms and two hydrogen atoms so the atomic mass of calcium is 40.08 let me just confirm the periodic table and yeah that's about right and oxygen is 16 hydrogen is 1.008 so the molar mass is 74.096 grams per 1 mole so now that we have the moles of calcium hydroxide we need to divide it by the liters of solution now we have 850 milliliters which is the same as 0.85 liters to convert milliliters into liters divide by thousand keep in mind one liter is thousand milliliters so now we have moles divided by liters and that's going to give us the molarity of the solution so it's 1.5 divided by 74.096 divided by 0.85 so the molarity is 0.0238 now that we have the molarity we can calculate the normality using this equation molarity times so the molarity is 0.0238 now what's in this problem calcium hydroxide has two hydroxide ions per formula unit so is two so the normality which i'm going to write it at the top it's point zero four seven six so that's the normality of the solution let's see if we can get that same answer using the second method so make sure you try to do it first before looking at the solution so let's start with one mole of plus now one mole of plus reacts equivalently excuse me equivalently with one mole of hydroxide so if you started with one mole of plus or one mole of hydroxide you can still get the right answer just have the habit of starting with one mole of plus now one mole of calcium hydroxide contains two moles of hydroxide ions so now we could cancel these units and now let's convert moles to grams using the molar mass and the molar mass for calcium hydroxide is 74.096 grams per 1 mole so it's going to be 1 times 74.096 divided by 2. and so this is equal to 37.048 grams so this is equal to the equivalent weight so one equivalent weight is 37.048 grams that's our conversion factor so 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 start with the mass of the substance the mass that's given to you so we have 1.5 grams of calcium hydroxide next using this conversion factor convert it to the number of equivalent weights so one equivalent weight is 37.048 grams now that you have the number of equivalent weights divided by the liters of solution so 850 milliliters as we said before is 0.85 liters so remember normality is the number of equivalent weights divided by the liters of solution so make sure that you end with those two units equivalent weights on top and liters in the denominator of the fraction so it's going to be 1.5 divided by 37.048 which tells us that we have .0405 number of equivalent weights and then divide that by 0.85 liters and so you get the same answer which is 0.0476 so now you have two ways in which to calculate the normality of the solution so hopefully you found this video to be helpful and thanks for watching you