In this video we're going to begin our lesson on pH and the pH scale. And so what's important to recall from some of our previous lesson videos is that the concentration of hydrogen ions is incredibly important when it comes to life. And this is because many biological processes in living organisms are strongly affected by the concentration of dissolved hydrogen ions. And so if the concentration of dissolved hydrogen ions is not in the correct range then the biological processes may not work because they are strongly affected by the concentration of hydrogen ions and so it's in the scientists best interest to be able to measure the concentration of hydrogen ions because it had such a strong effect on biological processes. And so this is exactly where the pH comes into play and this is because the pH is really just a logarithmic measurement of the hydrogen ion concentration in a solution. And so by using the pH the scientists can determine the amount of hydrogen ions in a solution and once again the concentration of hydrogen ions strongly affects biological processes. So it's important for scientists to be able to measure hydrogen ion concentration using pH. Now it's also important to keep in mind that the pH not only is a direct measurement of hydrogen ion concentration but it is also able to indirectly measure the hydroxide ion concentration or the o h minus ion concentration in aqueous solutions where the solvent will be water. Now the pH scale is a scale that goes from 0 at its minimum to 14 at its highest and the pH scale can be used to determine if a solution is going to be acidic or basic. And so if we take a look at this table down below, we'll be able to see how the pH scale can really be broken up into 3 different sections and that's what each of these three rows in this table represents. And so when the pH what's important to know is that the pH scale is actually centered around a value of 7. And so, a pH of 7 is right in the middle of 0 and 14. And so when the pH is lower than 7, this is when we have an acidic solution. And so acidic solutions have very low pHs and so the solution pH is going to be lower than 7 when we have an acidic solution. Now on the other hand, when we have very high pHs above a pH of 7, then we have a basic solution. So basic solutions, the solution pH is going to be greater than a value of 7. And then of course neutral solutions are going to have a solution pH that is exactly equal to 7. Now another important detail to keep in mind is that the value of the pH is actually inversely proportional to the value of the concentration of hydrogen ions. And so what this means is that when the pH is really really really low like in acidic solutions, the hydrogen ion concentration will be really really high. And so we can go ahead and draw this in over here. When the pH is really really low then the hydrogen ion concentration will be very high. And, on the other hand when the pH is very high, then the hydrogen ion concentration will be very low and so, this is what we mean by inversely proportional. The fact that when the pH is low the hydrogen ion is high and when the pH is high the hydrogen ion concentration is low. And so taking a look at these acidic solutions in the first row again they have very very low pHs, pH levels are going to be below 7 in acidic solutions. And this means that the hydrogen ion concentration will be high. It will be higher than the hydroxide ion concentration in the solution. Now on the other hand for basic solutions where the pH values are very very high and the pH value is greater than 7, that means the hydrogen ion concentration will be very very low and so it will be lower than the hydroxide ion concentration which will be higher. And so when we have a neutral solution, where the pH is exactly equal to 7, what this means is that the concentration of hydrogen ions will be exactly equal to the concentration of hydroxide ions and so we'll be able to see this and visualize this even better as we take a look at our pH scale down below. And so what you'll notice is that this pH scale goes from a value of 0 at its minimum, which you can see is 0 right here on the left up to a value of 14 at its highest. And notice that a pH of 7 is right in the middle. Now, again you can see by the color coding here, the acidic solutions are somewhat reddish and the basic solutions are somewhat bluish and so you can see that this pH scale is kinda broken up into sections. Any pH that is below 7 is going to be an acidic pH and so the lower the pH is the more acidic it is. So we can label this as more acidic and then on the other hand any pH value that is greater than 7 is going to be a basic solution and so the greater it is the more basic it is. And then of course a pH value of exactly equal to 7 is going to be neutral pH. And so you can see many different examples of, different solutions that are going to have different pH's. And so notice that battery acid has a very very low pH, very acidic pH. Lemon juice has a pH of around 2. Tomato juice is around 4.2 or so. Black coffee is around pH of 5. Milk is slightly acidic. And then we have pure water is right at a pH of 7. So pure water is a neutral solution. Notice that ocean water is slightly basic with a pH of about 8 and same with baking soda. Ammonia has a pH of about 12 so it is basic. Bleaches right in between 12 and 13 and drain cleaner has a pH of about 14. And so you don't need to memorize all of these different solutions but it is interesting to see how these different solutions can have different pHs and different concentrations of hydrogen ions. And so once again it is important to know that the lower the pH value is the higher the hydrogen ion concentration. And so, if we take a look at this, what you'll notice is that when we have a very low pH, the hydrogen ion concentration will be very high. And so over here, we have an arbitrarily high number of hydrogen ions just to show you that acidic pHs are associated with high hydrogen ion concentrations. Just like what we said here, low pHs have high hydrogen ion concentration. And so, notice that as the pH values are increasing, the hydrogen ion concentration decreases and so over here on the far right what we can do is just put 1 hydrogen ion just an arbitrary number to show that basic solutions will have a low number of hydrogen ions. Now notice that the hydroxide ion concentration is, directly proportional to the pH which means that the higher the pH, the higher the hydroxide ion concentration. And so notice here we put an arbitrarily high number of hydroxide ions, when the pH value is high. And as the pH value gets lower, the hydroxide ion concentration also gets lower. And so over here we can put 1 hydroxide ion, an arbitrary number here just to indicate that low pH's have low hydroxide ions. And so, the relationship between the pH and the hydrogen ions is opposite of the relationship between the pH and the hydroxide ions. And so when we have a pH that is exactly equal to 7 such as pure water, then what we're saying is that the concentration of hydrogen ions is exactly equal to the concentration of hydroxide ions And again this is going to be true right at a pH of 7 just as we indicated up above in this table. And so, really to visualize this a little bit more clear notice that when the pH is low the concentration of hydrogen ions is really high and as you go over to the right when the pH is lower the hydrogen ion concentration is also lower. Whereas for the hydroxide ions notice that the pH is high when the hydroxide ion concentration is high. And as you go to the right the Hydroxide ion concentration gets lower and lower and lower. And so once again the concentration of hydrogen ions is going to be incredibly important to living systems and can affect many biological processes. And so, having the pH scale is allowing scientists to measure the concentration of hydrogen ions and therefore be able to determine the effect of the hydrogen ion concentration on biological processes. And so this is very important to keep in mind. And so this here concludes our brief introduction to pH in the pH scale and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.
2
Problem
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.
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
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.
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
Video duration:
5m
Play a video:
Video transcript
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 7 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 7, in its neutral range. And so in order to make sure that the pH stays around 7, 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 can 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 of 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 homeostasis in 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 pH h scale, which we know goes from 0 up to 14. And we know that values of 0 are going to be acidic, and values of 14 are going to be basic. And then, of course, right in the middle with a value of 7, that is going to be neutral. And once again, most living organisms require pH of about 7, in order for them to survive. And if the pH were to tip to either side, if, too much acid was added, that could tip the scales towards the acidic side. That could be really harmful for a cell. 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 cell's best interest to make sure that the pH is maintained and that the the pH is able to resist changes, 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 2 molecules that we see here, HCO3 minus and HHCO3. 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 many hydrogen ions there are. And so if there are a lot of hydrogen ions, then we would have a 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's no h plus anywhere, that means that the pH is going to be high and it's gonna be a basic solution. And so, what you'll notice here is that it says that h c o three minus is part of a buffer system because h c o three minus is 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, bi carbonate can act to lower the hydrogen ion concentration by accepting hydrogen ions. And that is gonna cause the pH, 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 HCO 3 minus accepts hydrogen ions. However, if the hydrogen ion concentration were to get too low, then this h h c o 3 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 HCO3- here and HH c o 3, are capable of either decreasing or increasing the hydrogen ions in the solution. And this is once again going to help maintain homeostasis in regards to the pH. And so this here 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
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.
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.