What is the hydroxide ion concentration of the lake described in question 3? a. 10−10 M b. 10−4 M c. 10−7 M d. 10.0 M

Video transcript

I know. This question asks if the ph of the lake is five, then what will be the hydroxide concentration of that lake? So let's think about what information were given in this problem. We have the ph value of the lake which is equal to five and we're looking for the hydroxide ion concentration of the lake. So what equations do we have that might help us get from P. H. 20. H minus concentration? Well we have the equation ph Plus p. o. h equals 14 in a water solution or in a lake, that's what we have. And then we have the equation, P. O. H. Is equal to negative log of O. H minus concentration. So those equations will get us from what we're given to what we're looking for. So first of all we'll go ahead and solve this equation for P. O. H. So that's equal to 14 - the ph value. We know that our ph value is five, so P. O. H equals 14 minus five which is equal to nine. Now we come on over here, the P O. H is equal to the negative log of O H minus concentration. It's also equal to nine. So if we multiply both sides by negative one, we have the log of O. H minus concentration is equal to negative nine. So therefore we must know that the O. H minus concentration Must be 10 to the - and the units are moller for concentration. So let's head on over to our answers and see if that's one of the choices we look at choice a Indeed, it is 10 to the -9 Mueller. So right away, there we go. We have a correct answer and we'll see you in the next video.