What is the pH of the buffer solution that contains 2.2 g of NH4 Cl in 250 mL of 0.12 M NH3 ? Is

What is the pH of the buffer solution that contains 2.2 g of...

Key Concepts

Buffer Solutions

A buffer solution is a mixture that resists changes in pH when small amounts of acid or base are added. This is achieved by combining a weak acid with its conjugate base or a weak base with its conjugate acid, allowing the solution to neutralize added acids or bases without a dramatic change in pH.

Henderson–Hasselbalch Equation

The Henderson–Hasselbalch equation is a simplified way to calculate the pH of a buffer solution. It relates the pH to the pKa (or pKb in the case of a base buffer) and the ratio of the concentrations of the conjugate base and acid, making it a vital tool for understanding and designing buffer systems.

Acid–Base Equilibrium

Acid–base equilibrium refers to the dynamic balance between acids and bases in a solution, which is described by equilibrium constants (Ka for acids and Kb for bases). This concept underpins the behavior of buffers, as the equilibrium between the weak acid and its conjugate base allows the pH to remain relatively constant.

Stoichiometric Calculations in Solution Chemistry

Determining the concentration of species in solution often involves stoichiometric calculations where the mass of a substance is converted to moles, and those moles are related to the volume of the solution to obtain molarity. These calculations are crucial for setting up the proper ratios in buffer systems.

Transcript

00:02 So this question is asking us to calculate the ph of a solution of ammonium chloride and ammonia.

00:11 So first of all, this is what is called a buffer solution.

00:15 And a buffer solution is a solution of an acid and its conjugate base, or in this case, it's a base and its conjugate acid.

00:27 And what that does, it creates a solution where if you add, small amounts of strong base or strong acid, the solution will resist change in ph.

00:40 So the ph will not change very much.

00:45 So the way we're going to calculate the ph of the solution is with the henderson -hassabuck equation, which i have written in black up here and underlined in red.

00:55 And it states that the ph of the solution is equal to the p .k .a.

01:01 Of the acid or base, which in this case will be ammonia, which the ka is 5 .6 times 10 to negative 10th.

01:10 And the pca is just a measure of how acidic or basic a substances, an acid or basis.

01:24 And then to that we'll add the log of the concentration of the conjugate base, which will be in this case ammonia over the concentration of the acid, which in this case will be ammonium ions.

01:46 So the first thing that we have to do is we have to calculate the concentration of ammonium ions.

01:53 And to do that, we're given grams of ammonium chloride and here is the molar mass of ammonium chloride.

02:03 And then we also know that the volume of the solution is going to be 250 milliliters, 250 milliliters, which is also 0 .25 .25 liters.

02:23 0 .25 liters, 0 .250 liters for adhering to significant figures.

02:34 And so what we're going to do, we're going to start with, we have 2 .2 grams, of nh4cl of nh4cl i messed up a little there writing nh4cl and then we know that we can divide that by the molar mass to get the number of moles of ammonium chloride that we're going to be putting in the solution grams per mole so we have 2 .2 divided by 53 .49 and we can use a calculator to show that we have 0 .041 moles of nh4cl.

04:04 And then we know that we have 250 milliliters.

04:10 So we can divide 0 .041 moles by 0 .25 liters to get moles per liter.

04:21 And that'll give us our concentration of nh4 cl.

04:30 So that's going to end up being 0 .16.

04:43 Configures at the end, but this is, i will write a capital m for molar.

04:53 So that's the concentration of nh4 plus ions in the solution...

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