Calculate the pH and pOH of the solutions with the following hydronium ion or hydroxide ion conc

Calculate the pH and pOH of the solutions with the following...

Key Concepts

Relationship between pH and pOH

In aqueous solutions at standard conditions (25°C), there is a fixed relationship between pH and pOH expressed by the equation pH + pOH = 14. This relationship allows the determination of one value when the other is known, linking the measures of acidity and basicity in a single coherent framework.

Acid-Base Classification

This concept involves determining whether a solution is acidic, basic, or neutral based on its pH or pOH value. Solutions with pH values less than 7 are classified as acidic, those with pH values greater than 7 as basic, and those with a pH of exactly 7 as neutral. This classification is essential in understanding chemical reactivity, biological systems, and environmental conditions.

pOH Scale

The pOH scale measures the concentration of hydroxide ions in a solution, calculated as the negative logarithm of the hydroxide ion concentration. Just like the pH scale, it provides an indirect way to express the concentration of a particular ion in a form that is easier to conceptualize and compare.

pH Scale

The pH scale is a quantitative measure of the acidity or basicity of an aqueous solution. It is defined in terms of the hydronium ion concentration, where lower pH values (typically less than 7) indicate acidic solutions, pH 7 is neutral, and higher pH values (typically greater than 7) indicate basic (alkaline) solutions.

Logarithmic Calculations

This concept involves using logarithms to convert ion concentrations into pH or pOH values. In particular, the negative logarithm (base 10) of the hydronium ion concentration gives the pH, and similarly, the negative logarithm of the hydroxide ion concentration gives the pOH. This mathematical conversion is fundamental in expressing very small ion concentrations in a manageable numeric scale.

Transcript

00:01 In this problem, we are given a few h3o plus and oh minus concentrations, and we want to find the ph and the p -o -h of each of the following.

00:11 So we've got a and b, they give us oh -minesonsentrations, and c -n -d, we have h -3 -0 -plus concentrations.

00:19 And for each of these, we want to find ph and p -o -h.

00:23 So if we have an h -3 -o concentration or an o -h -mineous concentration, if we take the negative log of either of those, so whether we have oh minus or h3o plus, if we take the negative log of either one of those, we will get either p -o -h or p -h respectively.

00:50 So looking at this, if we take the log of o -h -mineas, we end up with p -o -h, and if we take the log of h -h, h3o plus, we end up with ph.

01:05 So, and then knowing that if we take 14 minus either ph or p -o -h, we end up with the opposite.

01:17 So 14 minus ph would give us p -o -h, and 14 minus p -o -h would give us ph.

01:24 So knowing these little tricks, these little math techniques, we can figure out the answer to these relatively quickly.

01:31 So if we've got the oh minus in our first problem, and we want to do the, we want to find our p -o -h, we would do negative log of 8 .2 times 10 to the negative 11th, and that will give us our p -o -h, which in this case is going to be 10 .09.

01:57 Now, doing the acid portion of this, if we take 10 minus, or no, not 10, my apologies, we've got 14 minus 10 .09, that will give us 3 .91 for our ph.

02:20 So for our first problem, we've got a p .o .h of 10 .09, using taking the negative log of our o .h concentration.

02:29 And if we take our poh and subtract it out of 14, we get our ph.

02:36 So for our first problem, these are two entries.

02:38 P -o -h is 10 .09 and ph equals 3 .91.

02:43 And if you want to check this, you can add them back together as long as it equals 14.

02:47 You've likely found the correct answer.

02:49 Just make sure that when you put the negative log of this number in scientific notation that you have it put in correctly, parentheses will be your best friend.

02:58 If you're ever wondering if you've done it wrong, do it several times and just make sure the number makes sense.

03:04 So if we go on to our second one, again, i'll use blue for our p -o -h and red for our ph.

03:11 So if we take the negative log of our number here, 7 .7 times 10 to the negative 6, that will give us 5 .11.

03:22 And if we subtract, well, remember that's our p -o -h because we did that to our o -h concentration.

03:29 Now if we take that number out of 14, we are left with 8 .89 for our ph.

03:39 So for our second problem, this is our ph, and this is our p -o -h.

03:47 So for our first problem, we got these two numbers.

03:50 For our second problem, we get these two numbers.

03:52 Now we switch things up for c &d, so i'm going to continue using red for our ph and blue for our p -o -h.

04:00 So here we have our h -30 plus concentration.

04:03 Always know what you're taking the log of, or you could get the exact opposite answer of what you want.

04:10 So negative log of 3 .2 times 10 to the negative fourth, and that will give us 3 .49 for our ph.

04:19 So we've got that for our ph...

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