Calculate the pH of a solution containing 10 mg Ca(OH)2 in 200 mL of water. Mr Ca(OH)2 = 74.
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Answer:
we are trying to find out the pH of a solution that is one times 10 to the negative. Seventh. An air wage. Um, any wage does associate completely. So we don't have to worry about equal equilibrium. Constant here. Um, all of that will produce away h minus when putting solution. So let's go ahead. Get started. Remember, water itself sell fine Isis forming h plus and which, minus eso in this problem, I am going to have the h plus concentration equal ex, except that equal to my ex. And that, of course, would be moles per later. Because it's a concentration, right? If h plus his ex from the self ionization of water, we would also get X. But then because we're adding an a o. H, we have that 10 to the negative seventh moles per liter. Okay, so that is going to give us the total amount of O. H minus in solution. Okay. Recall also that the k w for water. In other words, when the concentration of H plus is multiplied by the concentration of O H minus, we look at 10 to the negative 14th for one times 10 to the negative 14th, whichever way you'd like to write it. All right, So we have this equation. I am going to plug in my values for H Plus and my values for O H minus, except those equal to 10 to the negative 14. Let's go ahead and do that. So X Times X plus 10 to the native seventh equals 10 to the negative. 14th. Um, distributing this X here we get X squared plus 10 to the negative, seventh X, and then I'm gonna subtract the 10 to the negative 14th from each side two. Complete my quadratic equation here so that would be equal to zero. All right, so we have a quadratic equation grabbing a handy dandy quadratic formula calculator. We get two possible values for X X. Could be 6.18 times 10 to the negative eight. Okay, or X Could be negative. 1.618 Yeah, times 10 to the negative seventh. Oh, well, we cannot have a negative concentration. Remember, X was our hydrogen ion concentration. We can't have a negative polarity, so we know that X or the concentration of H plus is 6.18 times 10 to the negative eighth. Now all we need to do is calculate the pH. Remember that pH is the negative log of the H plus concentration. So plugging in my value here, 6.18 times 10 to the negative eight. Using my calculator, I hit a pH of 7.2. Right. So the ph for the solution be 7.2. Thanks. So thanks so much for watching.