Calculate the pH and the concentrations of all species present
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Question

Calculate the pH and the concentrations of all species present 
(H3O+ , F-, HF, Cl-, and OH-) in a solution that contains 
0.10 M HF 1Ka = 3.5 * 10-42 and 0.10 M HCl.

Accepted Answer

Hello. Everyone in this video. We want to find the concentrations of H 30 plus B. R minus H. And three. And and three minus. As well as the ph of the 0.15 molars of H. and three were given the K. value here. And we have the 0.15 molar of hbr solution. So the solution contains this and this here. All right. So our H P R H B R. This is a known strong acid. So basically we can use this to be the H 30 plus concentration, which is equal to the concentration of R. B. R minus. And this is just 0.15 molars. And we are being asked remember for the concentration of H. 30 plus and B. R minus. So here we have two answers already. All right now, for R. H. N. Three this is a week acid. So the concentration of H. 30 plus is equal to 0.15 molars. This realm are hbr H 30. Is our from the H N three is negligible. So we just have that. But we already said that the H 30 concentration is 0. already. But we're just going in further as to how this is all right. So for my K. A. How we get this is well, we have the concentration of our H. 30 plus, multiplied by the concentration of N three minus all over the concentration of H. N. Three. So we already have the K. A value. Of course and that is 1.9 times 10 to the -5. Alright and let's see here we have 0.15 times x. We all know the concentration of N three minus Divided by 0.15 -X. And let's take a step backwards here. 0.15, divide by 1.9 times 10 to the -5 here. This value is going to be a lot Greater than our 500. So we go ahead and ignore our minus x value. So we're just kind of getting rid of this here. So then we have 1.9 times 10 to the negative five equaling to 0.15 times our X divided by 0. of course then we can see here, we just need to solve for X. And once we do we get this value which is just the concentration of R, N three minus to be equal to 1.9 times 10 to the negative five molars. So we have found the concentration of the N three minus here. So that's another answer there. Of course the H and three, we'll just have it here. Actually that is equal to 0. Molars and this is the concentration of H and three. So then we have this answer as well for this right here. Alright, lastly of course is just R. P h. Well maybe just do it on the right here. So P H is equal to the negative log of our H 30 plus, which is 0.15 molars. So P H is equal to negative log 0.15. Once you put that into the calculator, we see that my Ph is then equal to 0.82. So this is going to be my last and final answer for this problem. Thank you all so much for watching.

Calculate the pH and the concentrations of all species present (H3O+ , F-, HF, Cl-, and OH-) in a solution that contains 0.10 M HF 1Ka = 3.5 * 10-42 and 0.10 M HCl.

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