Difference Between Molarity and Normality | Definition, Units and Calculations, Relationship
Different concentration units are used for expressing the concentration of solution .like some time percent solution,molar solution, what is meant by percent. Molarity and normality are directly related to each other but density and normality are not. For definitions of molarity and normality, refer to my. As a supplement to your lecture, it can help them achieve molarity, molality, and whereas molality is a measurement of the moles in relationship to the mass of.
Therefore a measure of molar concentration based on the volume of liquid that a substance is dissolved in.
Difference Between Molarity and Molality | Difference Between | Molarity vs Molality
It is important to realize that the volume is in liters so you may have to convert first if you have volume in ml for example.
To prepare a molar concentration one adds a known quantity of solute to a volumetric flask then fills up the flask with liquid until the 1 liter mark is achieved. The weight of the sugar first has to be converted to moles and then the water is added until 1 liter is reached. To calculate molarity you need the solute in moles, but usually you will have a certain weight of solute which means you first need to convert the grams into moles. This can be done by finding the molar mass of the solute from the periodic table.
The molar concentration formula can be rearranged to solve for both volume and moles. Volume is influenced by changes in temperature or pressure.
For instance, the volume would increase with increasing temperature. This means that there will be some question of accuracy where there are changes in temperature. If temperature decreases enough then the liquid may contract causing the molarity to increase because the same number of moles remains but there would be less solution. Conversely, if the temperature increases enough then the liquid may expand causing the molarity to decrease because the same number of moles remains but there would be more solution present.
Molarity can be used to calculate the concentration of a substance that has been diluted. Molarity can be used when exact precision is not required.
It is however influenced by changes in temperature because it is a volumetric measurement, so in some cases it may not be appropriate to use. Molarity and molality can be the same in some cases. For instance 1 liter of water weighs 1 kg. Molality can be defined as the number of moles of substance known as the solute that is found in a certain mass of solvent given in kg, that it is dissolved in.
The formula for calculating molality is: When you increase the amount of OH, you would decrease the pOH, right?
And that's just because it's the negative log. And just think OH-- you're making it more basic.
Difference Between Molarity and Normality
And a high pH is also very basic. If you have a mole of this, you end up with a pH of And if you had a strong acid, not a strong base, you would end up with a pH of 0.
- Buffers and Henderson-Hasselbalch
- Molarity, Molality, or Normality? (A Quick Review)
Hopefully you're getting a little bit familiar with that concept right now, but if it confuses you, just play around with the logs a little bit and you'll eventually get it. But just to get back to the point, if you just did this in water, you immediately get a super high pH because the OH concentration goes through the roof.
But if you do it here-- if you apply the sodium hydroxide to this solution, the solution that contains a weak acid and it's conjugate base, the weak acid and its conjugate base, what happens? Sure, it immediately reacts with all of this hydrogen and eats it all up. And then you have this extras supply here that just keeps providing more and more hydrogens.
And it'll make up a lot of the loss. So essentially, the stress won't be as bad. And over here, you dramatically increase the pH when you just throw it on water. Here, you're going to increase the pH by a lot less.Relation between Molarity(M) and molality(m)
And in future videos, will actually do the math of how much less it's increasing the pH. But the way you could think about it is, this is kind of a shock absorber for pH. Even though you threw this strong based into this solution, it didn't increase the pH as much as you would have expected. And you can make it the other way. If I just wrote this exact same reaction as a basic reaction-- and remember, this is the same thing.
So if I just wrote this as, A minus-- so I just wrote its conjugate base-- is in equilibrium with the conjugate base grabbing some water from the surrounding aqueous solution. Everything we're dealing with right now is an aqueous solution. And of course that water that it grabbed from is not going to be an OH.
Remember, are just equivalent reactions. Here, I'm writing it as an acidic reaction. Here, I'm writing it is a basic reaction. If you were to add a strong acid to the solution, what would happen? So if I were to throw hydrogen chloride into this. Well hydrogen chloride, if you just throw it into straight up water without the solution, it would completely disassociate into a bunch of hydrogens and a bunch of chlorine anions.
And it would immediately make it very acidic.
You would get to a very low pH. If you had a mole of this-- if your concentration was 1 molar, then this will go to a pH of 0. But what happens if you at hydrochloric acid to this solution right here? This one that has this weak base and its conjugate weak acid? Well, all of these hydrogen protons that disassociate from the hydrochloric acid are all going to react with these OHs you have here.
And they're just going to cancel each other out. They're just going to merge with these and turn into water and become part of the aqueous solution. So this, the OHs are going to go down initially, but then you have this reserve of weak base here. And Le Chatelier's Principal tells us. Look, if we have a stressor that is decreasing our overall concentration of OH, then the reaction is going to move in the direction that relieves that stress.
So the reaction is going to go in that direction. So you're going to have more of our weak base turning into a weak acid and producing more OH. So the pH won't go down as much as you would expect if you just threw this in water. This is going to lower the pH, but then you have more OH that could be produced as this guy grabs more and more hydrogens from the water. So the way to think about it is it's kind of like a cushion or a spring in terms of what a strong acid or base could do to the solution.
And that's why it's called a buffer.
solutions - What is the relation between molarity and molality? - Chemistry Stack Exchange
Because it provides a cushion on acidity. If you add a strong base to water, you immediately increase its pH. Or you decrease its acidity dramatically. But if you add a strong base to a buffer, because of Le Chatelier's Principal, essentially, you're not going to affect the pH as much. If you add and acid to that same buffer, it's not going to affect the pH as much as you would have expected if you had thrown that acid in water because the equilibrium reaction can always kind of refill the amount of OH that you lost if you're adding acid, or it can refill the amount of hydrogen you lost if you're adding a base.
And that's why it's called buffer. It provides a cushion. So it give some stability to the solution's pH. The definition of a buffer is just a solution of a weak acid in equilibrium with its conjugate weak base. That's what a buffer is, and it's called a buffer because it provides you this kind of cushion of pH.
It's kind of a stress absorber, or a shock absorber for the acidity of a solution. Now, with that said, let's explore a little bit the math of a buffer, which is really just the math of a weak acid.
So if we rewrite the equation again, so HA is in equilibrium. Everything's in an aqueous solution. With hydrogen and its conjugate base. We know that there's an equilibrium constant for this. We've done many videos on that. The equilibrium constant here is equal to the concentration of our hydrogen proton times the concentration of our conjugate base.
When I say concentration, I'm talking molarity.
Difference Between Molarity and Molality
Moles per liter divided by the concentration of our weak acid. Let's solve for hydrogen concentration. Because what I want to do is I want to figure out a formula, and we'll call it the Hendersen-Hasselbalch Formula, which a lot of books want you to memorize, which I don't think you should.
I think you should always just be able to go from this kind of basic assumption and get to it. But let's solve for the hydrogen so we can figure out a relationship between pH and all the other stuff that's in this formula. So, if we want to solve for hydrogen, we can multiply both sides by the reciprocal of this right here. And you get hydrogen concentration. Ka times-- I'm multiplying both sides times a reciprocal of that. So times the concentration of our weak acid divided by the concentration of our weak base is equal to our concentration of our hydrogen.
Let's take the negative log of both sides.