What is the pH of an aqueous solution of Ca1OH22 at 25.0 °C with a concentration of 6.3 * 10-5 M? (LO 16.7) (a) 4.20 (b) 10.10 (c) 11.36 (d) 9.80

Video transcript

Hello everyone today. We have the following question, calculate the ph of a 2.64 times 10 to the negative third molar solution of magnesium hydroxide at 25 degrees Celsius. So first we want to make note that magnesium hydroxide magnesium hydroxide is a strong base. And so what does this mean? This means that if we were to place this in a solution of course it would disassociate or break apart into magnesium two plus ions as well as Hydroxide ions and 2 to be exact from this, we can solve for our concentration of our hydroxide ions would be and so to do that we simply take the concentration of hydroxide ions is equal to And we have two of them. We have two hydroxide ions. And we're actually gonna multiply this by the polarity which is 2.64 times 10 to the negative third. No we do that. We get a concentration of 5.28 times 10 to the negative third molar. So we're gonna save that number for later. The next thing we're gonna do is we're gonna try and solve for R. P. O. H. And we can do that with our concentration of hydroxide islands. And in doing that we use the equation that the P. O. H. Is equal to the negative log of the concentration of our hydroxide ions. When we plug in our value for the concentration of hydroxide ions, we get the negative log of 5.28 times to the negative three Mueller. And then we ultimately end up with a p. o. h of 2.274, 2.2774. Our last step is to finally calculate the ph and if we have the p o H, we can use the formula that the ph plus the P O H Is equal to 14. Rearranging this equation. We have, the ph is equal to 14 minus the p o. H, which in this example was found to be 2.2774. Will you plug into a calculator? We'll get a final ph of 11.7-3 as our final answer. Overall, I hope that this helped, and until next time.