Question
A saturated aqueous solution of Ca(OHlz has a pH of 12.25_ What is the [Ca2+] of such a solution?
A saturated aqueous solution of Ca(OHlz has a pH of 12.25_ What is the [Ca2+] of such a solution?
Answers
A solution saturated in calcium hydroxide (limewater) has a pH of $12.35 .$ What is $K_{s p}$ for calcium hydroxide?
To calculate the pH of this buffer solution. We simply need to know what the PK is and that was given to us at 4.75 And then we need to identify the concentration of the base, which in this case is ch three C to minus. And the acid, which is see, it's three CEO age. So pH is going to be equal to PKK, which is given to us for a CD Kassid, plus the log of the acid ate concentration, which is 0.4 divided by the gases concentration, which is 0.8 and pH is 4.45
Mhm. To determine the equilibrium constant for calcium hydroxide from a saturated solution for which we know a ph We first need to write the equilibrium reaction. It'll be calcium hydroxide dissociated into calcium ion plus two hydroxide and ions Ks. P. Is going to be equal to the calcium concentration, multiplied by the hydroxide concentration squared. We can get the hydroxide concentration from the ph first. We'll get the hydrogen ion concentration by recognizing that it is equal to 10 to the negative ph or 10 to the negative 12.35 giving us 447 times 10 to the negative 13. To get the hydroxide concentration, we simply divide this value into KW, which is a constant at 1.0 times 10 to the negative 14. Giving us a hydroxide concentration a 0.2 to four Mueller. The calcium concentration, we don't know but we can express it in terms of the hydroxide concentration, we get one calcium for every two hydroxide. So the calcium concentration must be one half the hydroxide concentration, assuming there's no other source of calcium or hydroxide in the solution. So the calcium concentration becomes 1.12 times 10 to the negative to moller Ks. P. Then is equal to the calcium concentration, which we just calculated multiplied by the hydroxide concentration, which we also determined, and we get an equilibrium constant that is 56 times 10 to the negative six.
We came today, I've been going over question number one or two. It's talks about calculating the pH. My museum hydroxide. So the reaction of magnesium hydroxide is mt. Or H two its first two mg two plus plus 20 it rings. So you have this will be X, this two X, But then, since your coefficient squared then in the back of the book, you find out that the K S P of magnesium hydroxide is 5.61 times 10 to the minus 12 is gonna be able to four x cubed, so derived by four. Thank you. Your answer. We'll take the key route on you get ecstasy shoe. So 0.0, because it was playing. 01 Well, I think there's two. You multiply it by two. It's the hydroxide is two X. What gives you point? 02? Then you take the negative log of it. Chicken. Yeah. Okay. To the minus four. Yeah, yeah. No. Which gives you three points 65 and then he subtract from 14. So it's gonna be 14 minus three points. 65 doing you 10.3 finds, which is gonna be
So we have, uh, 0.0 89 Moeller. Uh, sodium Hypochlorite sodium is a spectator in acid base reactions. It's not acid based active, but the hypo chloride ion is thes the conjugal base of the weak acid hypo Cloris acid. And so it will react as the base. And so I've written the KB reaction, the reaction of hyper gloried ion with water thehyperfix Orion will gain H plus. The water will lose it and make O H minus and from the reaction than the KB expression. Now you go to the table and you find a K A for, uh, hyper Cloris acid, but you don't find a K B. What you have to do is calculate the K B from the K W, and that is based on the relationship that four any weak acid and it's congregate base or a weak base and its consequent acid, the product of the two equilibrium constants will BKW only for a pair of Kontic. It's and so the value from the table is 2.9 times 10 to the minus eight for hyper Cloris acid. And so now this is like any other problem. Once we recognize those things that sodium is a spectator. So leave it out. All negative ions are basis, and all of those negative ions will react except the conjugal basis of strong assets. So standardized table ah, And now plugging those values into DKB expression X and X in the numerator and 0.0 89 minus sex in the denominator, and the K B is equal to three point four. I'm sending the minus seven, and that's a small K. And for that reason we're going to be able to drop to sex. And so X squared is equal to multiplying both sides. By this denominator, X squared is equal to 3.4 times 10 to the minus seven times 0.0 89 and X will be the square root of that. And so without rounding, I have just que From doing this calculation, I'm just gonna multiply by 0.0 a nine and then take the square root and I get 1.75 times 10 to the minus four, and that is Theo H minus concentration. And so the, uh, p o h we can get from the log of that. And so the p O. H is 3.76 and the pH and the P O. H have to some to 14 and so the Ph is 10.24.