 ## General Biology

Learn the toughest concepts covered in Biology1&2 with step-by-step video tutorials and practice problems by world-class tutors

1
concept

## pH Scale 7m
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in this video, we're going to begin our introduction to Ph and the pH scale. And so recall from our previous lesson videos, we mentioned that many biological processes are actually strongly affected by the concentration of hydrogen ions dissolved in the solution. And so it's really to the scientists interest to measure the concentration of hydrogen ions because once again, the concentration of dissolved hydrogen ions matters because it will strongly affect many biological processes. And so the measurement of the concentration of hydrogen ions is really where pH comes into play. And that's because Ph is really just a log arrhythmic measurement of the hydrogen ion concentration in a solution. And so, really, the pH can tell us how many hydrogen ions are found within a solution. Now the pH can also indirectly measure the hydroxide ion concentration or the O. H. Minus ion concentration and acquis solutions, and we'll be able to see this down below when we get to this part of our table. Now, the pH scale specifically goes from a value of zero up to a value of 14, and so, depending on where the pH falls on the PH scale, this will determine if the solution is acidic or basic. And so if we take a look at this table that we have down below, which will realizes that acidic solutions are going to be solutions that have a pH that is less than seven. If the pH is less than seven, then we have ourselves an acidic solution now. A basic solution, on the other hand, is actually a solution. Who's Ph is greater than seven. And then, of course, if the pH is exactly equal to seven, then we have ourselves a neutral solution. And so neutral solutions have a pH that is exactly equal to seven now, when it comes to the hydrogen ion concentration and the hydroxide ion concentration, which will realize is that the pH values are actually inversely related to the concentration of hydrogen ion. And so what that means is, the lower the pH is, the greater the hydrogen ion concentration and so acidic solutions actually have really, really high hydrogen ion concentrations that are greater than the hydroxide ion concentration and so H plus concentration will be greater than O. H minus concentration in acidic solutions and basic solutions. On the other hand, the higher the pH is the lower the concentration of hydrogen ion. And so that means that in basic solutions, we can say that the hydrogen ion concentration will be smaller than the hydroxide ion concentration, which will be greater. And then, of course, right in the middle. If we have a neutral solution, who's pH is exactly equal to seven. What this means is that the hydrogen ion concentration is going to be exactly equal to the hydroxide ion concentration. And so what's really important to notice is how the acidic solution pH signed will flip when it's related to hydrogen ion concentration. So the smaller the pH, the greater the hydrogen ion concentration and the greater the pH of the solution, the smaller the hydrogen ion concentration. So if we take a look at the pH scale image that we have down below, we could go ahead and apply this so once again, notice that the acidic solutions which we have colored with a reddish background here are further to the left of our scale, whereas the basic solutions at the bottom here are further to the right of our scale. And then, of course, in the middle of the neutral solutions are right at a Ph of seven. And so what's important to note here is that the more acidic the solution is, the lower the pH value will be, and so notice that the pH value goes from a value of zero up to a value of 14, as we indicated up above here. And so the higher the pH is, the more basic the solution will be. And so what you'll notice is that throughout this pH scale, we have these different components that show you where they fall on the Ph scale so you can see battery acid has a pH that's associated with zero, so it's incredibly, incredibly acidic. Then you could see lemon juice here tomato juice where it falls. Black coffee milk is slightly underneath of Ph of seven, which means that it is slightly acidic. And then we have pure water right here in the middle as a neutral solution. And then you could see where ocean waterfalls, baking soda, ammonia bleaches and drain cleaner as well. And so one thing to note here is that once again, the lower the value of the pH, the Mawr hydrogen ions. There are so If we were to go ahead and fill in our hydrogen ions, we would see that there would be a lot of hydrogen ions over here towards the acidic end. Whereas towards the basic end over here there would be a small amount of hydrogen ions. So we could just put one over here just for simplicity and then notice that the hydroxide ion concentration is going to be flipped. And so what that means is the mawr acidic? The solution is, the lower the hydroxide high on concentration will be. So we'll just put one here just for simplicity. And then, of course, the higher the pH is the mawr hydroxide ions there will be. And so you can see that the pH will actually tell us the hydrogen ion concentration, which will basically be very, very high over here. And then, as it makes its way over, get smaller and smaller and smaller and smaller and then indirectly, it also tells us the hydroxide ion concentration, which is the inverse. It starts really, really high over here. And then, as it makes its way over, get smaller and smaller and smaller and smaller, And so right here in the middle where the pH is neutral. This means once again that the concentration of hydrogen ions gonna be exactly equal to the concentration of hydroxide ion. So for here in the middle, what we can say is when the P H is equal to seven theme number of hydrogen ions which will just go ahead and put us to hear is gonna be exactly equal to the number of hydroxide ions which will put here as to as well. And once again, this is what happens when the pH is exactly equal to seven. So this is, uh, the neutral pH. And so really, this year concludes our lesson. Our introduction to Ph and the PH scale and the best way to get this down is to get some practice with it. So we'll be able to see you in our next couple of videos to get some more practice
2
Problem

In a neutral solution, the concentration of __________.

a) Hydrogen ions is less than the concentration of hydroxide ions.

b) Water molecules is less than the concentration of hydroxide ions.

c) Hydrogen ions is greater than the concentration of hydroxide ions.

d) Hydrogen ions is equal to the concentration of hydroxide ions.

3
Problem

A base _______:

a) Has a value of 7 on the pH scale.

b) Is a chemical that donates hydrogen ions to a solution.

c) Is a chemical that accepts hydrogen ions from a solution.

d) Has a value below 7 on the pH scale.

e) None of the above are correct.

4
concept

## Buffers 5m
Play a video:
in this video, we're going to begin our introduction to buffers. And so first, we need to note that the pH of most living organisms is actually maintained right around a value of seven or having a neutral pH and changing the pH even slightly can actually be really, really harmful to living organisms. And so it's in the best interest of living organisms to make sure that the pH stays around seven in its neutral range. And so, in order to make sure that the pH stays around seven, living organisms use what are known as buffers. And so buffers are defined as substances that are capable of resisting changes in the pH even when acids and bases are added to the solution. So typically, acids and bases would change the pH. But if buffers are present in the solution, then even when acids and bases are added to the solution, the substance is capable of resisting changes in pH. Which means that the pH will not change. And once again this is beneficial for living organisms. Because if the pH changes too much, then that could be really, really harmful. And so these buffers are good things. That cells use to make sure that the pH is going to resist changes and stay in that neutral range. Now, depending on the situation, buffers are capable off either decreasing or increasing the concentration of hydrogen ions in the solution. And once again, living organisms are going to use buffers to help maintain the pH or help maintain home yo Stasis and regards to the pH values. And so if we take a look at our image down below, over here on the left hand side, notice that we're showing you a P H scale, which we know goes from zero up to 14. And we know that values of zero are going to be acidic and values of 14 are going to be basic. And then, of course, right in the middle, with the value of seven that is going to be neutral. And once again, most living organisms require pH of about seven on order for them to survive. And if the pH were to tip to either side If, uh, too much acid was added, that could tip the scales towards the acidic side that could be really harmful for herself, but also, if too much base was added that could tip the scale towards the base side. And that could also be really, really harmful. So once again, it's in the cells. Best interest to make sure that the pH is maintained and that the pH is able to resist changes s so that it stays about the same. And so here we're showing you in the example a specific type of buffer called the bicarbonate buffer system, which is found in our blood, and it helps to maintain the ph of our blood. And so what you'll see is over here on the right hand side, we're focusing in on the bicarbonate buffer system, which includes these two molecules that we see here H c 03 minus and H h c 03 And so notice that on the left hand side over here, we're showing you hydrogen ions. And remember that the pH is going to reflect how maney hydrogen ions there are. And so if there are a lot of hydrogen ion, then we would have an acidic solution, so this side over here would be the acidic side. But of course, if there are not many free hydrogen ions like over here notice there is no H plus anywhere. That means that the pH is going to be high and it's gonna be a basic solution. And so which will notice here is that it says that H C 03 minus is part of a buffer system because HBO three minuses capable it can accept hydrogen ions if the hydrogen ion concentration gets too high. And so in A. In a scenario, when the hydrogen ion concentration gets too high by carbon, it can act to lower the hydrogen ion concentration by accepting hydrogen ions, and that is going to cause the pH. Uh, it's gonna cause the reaction to go in this direction towards the right, which will increase the pH. And so the pH is increased when h. C 03 minus except hydrogen ions. However, if the hydrogen ion concentration where to get too low, then this H H C 03 over here is capable of donating hydrogen ions if it gets too low, and so you can see that depending on the situation, depending on if the hydrogen ions are too high or too low, buffers, which would include H. C 03 minus here and H H C 03 are capable of either decreasing or increasing the hydrogen ions in the solution. And this is once again going to help maintain home yo Stasis in regards to the pH. And so this year concludes our introduction to buffers, and we'll be able to get some practice applying these concepts, moving forward in our course, so I'll see you all in our next video.
5
Problem

Which of the following statements about buffers is true?

a) They maintain a consistent pH only when acids are added to them, but not bases.

b) They maintain a consistent pH of 7.

c) They fluctuate in pH when acids are added to them.

d) They maintain a consistent pH when acids or bases are added to them.

e) They fluctuate in pH when acids or bases are added to them. 