here. It tells us a weak acid has a. K. A. Of 5.35. What is the hydro knee? Um Ion concentration in a 0.10 molar solution of this weak acid. Now we know that we're dealing with a weak acid. And the general generic formula of a weak acid is H. A. Remember weak acids and weak bases react with water within solution. So this weak acid will react with water. It is the acid. So that means water is the base. Remember, according to Bronson Laurie theory, the acid donates an H. Plus. So what we're gonna create is a minus plus H. +30. Plus. We're dealing With an ice chart because we're dealing with a weak species anytime we're dealing with a weak acid, a weak base, we set up an ice chart. Remember in a nice chart we ignore solids and liquids. So this water which is a liquid is ignored. Our initial concentration is said to be .10 moller. We're not given initial concentration for products or they're both zero. Remember, we lose react ints in order to make products bring down everything. Since we're dealing with a weak acid, we want to use our acid dissociation constant or K. A. K. Is equal to products. Overreact ints. So our products multiply together, divided by our reaction on the bottom. Again, we ignore water because it's a liquid here. The issue is we don't have K. We have P. K. So we're gonna have to convert P. K. Into K. A. Here K. A. Equals 10 to the negative P. K. A. We plugged that PK Thou given to us of 5.35 n. That gives me 4.467 times 10 to the negative six. So that's my K. A. Which I'm gonna plug over here at equilibrium. Both my products are X. So X. Times X. Is X squared divided by what's on the bottom which is 0.10 minus X. Here we have this minus X. Although this is on a local chemistry, I want to be as precise as possible. If that X variable is insignificant enough, we can ignore it to determine if we can ignore it. We do the 5% approximation method. Now the 5% approximation method says that if I take my initial concentration of my weak species and I divided by its association constant which is K. In this in this case if I divide the initial by the K. A. And the ratio gives me a value greater than 500 then I can ignore that minus X. So my initial concentration is 0.10 moller we're gonna divide it by the K. We just found. So 4.467 times 10 to the negative six. When I do that it gives me 22,387 0.2 As a value. So that number is definitely greater than 500. So according to the 5% approximation method I can ignore that -1. There All we do now is we solve for X. So we're gonna multiply both sides by .10. So we're gonna have 4.467 times 10 to the -7 equals X squared We just want X. So we're gonna take the square root of both sides here. So when I take the square root of both sides here I get x equals 4.6 6. 8 times 10 to the -4 Molar. When I sold for X. Here, this X. Gives me this sex which is equal to H 30. Plus. Remember when we're setting up a nice chart for a weak acid or a weak base anytime we find X. That represents either my H 30. Plus concentration or my O. H minus concentration. Since I'm dealing with an acid here, it's gonna give me the H 30 plus concentration which is my hydro ni um ion concentration based on our answer option F would be the correct choice. So just remember some of the fundamentals that we went over in terms of this question. If we're dealing with a weak acid or weak base in order to find hydro knee, um ion concentration or hydroxide ion concentration, we'll have to set up some type of ice chart in order to solve for X. Once we do we'll have that number. If we wanted to go a step further, we could have taken the negative log of this concentration and that would have given me ph here Were not asked to find pH were just asked to figure out what the concentration is of hydro name ion. So we just stopped there for X being 6.68 times 10 to the negative for Mueller.
