Full transcript
0:00Everyone is always talking about this
0:02pH level . pH here , pH there . But I have
0:05no clue what that is . For guys like
0:08that , and also for those who want to
0:09review the topic , here's a short
0:11explanation of the pH value . Let's
0:19first take a look at what pH actually
0:21stands for . PH is an abbreviation for
0:24pondus hydrogenii , from Latin .
0:27Translated , that means something like
0:29weight of hydrogen . We can phrase that
0:31a bit better , specifically as the
0:33concentration of hydrogen ions in a
0:35solution . They are usually called
0:37protons , by the way , and this exact
0:39proton concentration is what our pH
0:41value describes . You might know this
0:44already , but if there are many protons
0:46in an aqueous solution , it's called
0:48acidic . Conversely , if there are very
0:51few , it's basic or alkaline . So , the pH
0:54value is a measure of the strength of
0:56the acid or base . The pH scale ranges
0:59from 0 to 14 . A value of 7 indicates
1:03that the solution is neutral . Values
1:05below seven are considered acidic , and
1:07values above seven are basic or
1:09alkaline . And the further away from
1:12seven , the stronger the acid or base .
1:15So why should a solution be acidic at
1:17low pH values , meaning it has a high
1:19proton concentration , and basic at high
1:22values ? As in , there would only be very
1:24few protons in it ? Based on what we
1:26just said , shouldn't it actually be the
1:27other way around ? True , you’re
1:29actually quite right about that . But
1:31the pH value doesn't indicate the
1:32proton concentration directly . That
1:34would be way too simple , as usual . It
1:36indicates the negative decadic
1:38logarithm of the proton concentration .
1:41Awesome . What does that mean now , and
1:43why go to all that trouble ? First of
1:45all , a decadic logarithm is nothing
1:47more than the common logarithm , or the
1:49logarithm to the base 10 . We can show
1:53what that is with a relatively simple
1:55example . Let's assume we have a proton
1:58concentration of one thousandth of a
2:00mole per liter , or 0.001 moles per
2:03liter . This can also be written as 10
2:05to the power of -3 moles per liter . The
2:09decadic logarithm of that would simply
2:11be -3 , the exponent attached to the 10 .
2:14But now we have to take the negative
2:16value of that . So , we end up with a pH
2:18value of 3 . Quite low and acidic . Now
2:22for a second example with a relatively
2:24low H + concentration of 0.00001 moles
2:29per liter . Expressed differently , that
2:31would be 10 to the power of -9 moles
2:33per liter . The decadic logarithm would
2:35be -9 . The negative value of that is 9 ,
2:38which is higher and therefore basic .
2:41Okay , that’s how you get from proton
2:43concentration to the pH value .
2:45Additionally , we can see right here
2:47that smaller concentrations result in
2:49higher pH values . So it actually checks
2:52out . But why make such a fuss about it ?
2:56It's quite simple , you saw for
2:58yourselves that the proton
2:59concentrations had very low , cumbersome
3:01values . The resulting pH values are
3:04simply much more practical . Because of
3:07the tiny concentrations , which can be
3:09well below a mole per liter , you also
3:11get negative values . Positive ones are
3:14easier to calculate with , so you just
3:16flip the sign to make them positive .
3:18That's just how it's defined , and if
3:20you know that , you can calculate back
3:22to get from the pH value to those
3:24ridiculously tiny concentrations . And
3:26how do you know what pH value a
3:28solution has ? There are several ways to
3:31do that . The most common one among them
3:33is universal indicator paper . You can
3:36learn how that works right here in this
3:38video . And one last question : why are
3:42we even interested in the pH value ?
3:44Well , anyone who has ever put their
3:46hands into acid or lye knows why .
3:49Anything too acidic or too basic
3:50attacks the skin . So it would be good
3:53to know beforehand what pH something
3:54has . And that applies not only to skin ,
3:56but to all sorts of things . The pH
3:58value also influences chemical
4:00reactions . They can sometimes run quite
4:02differently in an acidic environment
4:04than in a basic one . Short and sweet .
4:07That’s how we all like it . We’ve
4:09covered the importance of pH values . If
4:11you want to know more about it , just
4:13come to simpelclub.de and use the
4:14search bar . The site is really awesome .
4:17So check it out . Yeah , good . That’s
4:21enough for now . So , see you in the next
4:23video .