Introduction to pH | Biology foundations | High school biology | Khan Academy

00:05:21
https://www.youtube.com/watch?v=oda2K4IFBaE

Sintesi

TLDRThe video discusses acidity and the pH scale, explaining that pH stands for power or potential of hydrogen. It describes the scale from 0 to 14, with values below 7 being acidic, 7 neutral, and above 7 basic. Acidic substances like fruits and basic substances like bleach are provided as examples. The video warns against consuming extreme pH substances due to their harmful effects. It also clarifies that the pH scale is logarithmic, meaning each unit change represents a tenfold difference in acidity or basicity. The importance of pH in biological contexts and medicine is also highlighted.

Punti di forza

  • 🔍 pH stands for power or potential of hydrogen.
  • 📊 The pH scale ranges from 0 (acidic) to 14 (basic).
  • 🍋 Acidic examples include lemons and orange juice.
  • 🧴 Basic examples include bleach and ammonia.
  • ⚠️ Highly acidic or basic substances can be harmful.
  • ⚖️ Neutral pH is around 7, like blood and seawater.
  • 🔄 The pH scale is logarithmic, not linear.
  • 🔬 pH influences chemical reactions in biology.
  • 🩺 Blood pH is crucial for health monitoring.
  • 🌍 pH balance is important in various scientific fields.

Linea temporale

  • 00:00:00 - 00:05:21

    The video introduces the concept of acidity and the pH scale, explaining that pH stands for either 'power of hydrogen' or 'potential of hydrogen'. It emphasizes the significance of hydrogen ions in determining acidity or basicity, with the pH scale ranging from 0 to 14, where values below 7 are acidic, 7 is neutral, and above 7 are basic or alkaline. Examples of acidic substances include fruits like lemons and grapefruits, while basic substances include bleach and ammonia. The instructor warns against consuming highly acidic or basic substances due to their potential harm. Additionally, the video discusses neutral substances like blood and seawater, and highlights that the pH scale is logarithmic, meaning each whole number change represents a tenfold difference in acidity or basicity.

Mappa mentale

Video Domande e Risposte

  • What does pH stand for?

    pH stands for power of hydrogen or potential of hydrogen.

  • What is considered acidic on the pH scale?

    A pH less than 7 is considered acidic.

  • What is considered basic on the pH scale?

    A pH greater than 7 is considered basic.

  • What are examples of acidic substances?

    Examples include lemons, grapefruits, and orange juice.

  • What are examples of basic substances?

    Examples include bleach, ammonia solution, and liquid drain cleaner.

  • Is the pH scale linear?

    No, the pH scale is logarithmic.

  • What happens if you ingest highly acidic or basic substances?

    They can cause serious damage to your cells and can be fatal.

  • What is a neutral pH?

    A neutral pH is around 7, examples include blood and seawater.

  • How does pH affect biological reactions?

    pH can influence the type of chemical reactions that occur.

  • Why is pH important in medicine?

    Doctors measure blood pH because deviations can cause serious health issues.

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Scorrimento automatico:
  • 00:00:00
    - [Instructor] What we're going to do in this video
  • 00:00:01
    is talk about acidity and in particular,
  • 00:00:02
    we're gonna talk about the pH scale.
  • 00:00:06
    Now the first question is what does pH stand for
  • 00:00:09
    and it turns out that there's some debate
  • 00:00:11
    why we have this lowercase p here,
  • 00:00:14
    we know why we have the h,
  • 00:00:16
    and some people will tell you it stands
  • 00:00:17
    for power of hydrogen, the capital h for hydrogen.
  • 00:00:22
    Some people will say it's the potential of hydrogen.
  • 00:00:27
    Some people will say it's the capacity for hydrogen,
  • 00:00:33
    you might say capacity doesn't start with a p
  • 00:00:35
    but if you go into Latin, it can.
  • 00:00:37
    But what do all of these things mean
  • 00:00:39
    and why do we care about hydrogen so much?
  • 00:00:43
    Well, it turns out that hydrogen, and in particular,
  • 00:00:45
    a hydrogen positive ion, and ion
  • 00:00:48
    is just a positively charged molecule,
  • 00:00:50
    that a hydrogen ion can play a major role
  • 00:00:53
    in how acidic or basic something is.
  • 00:00:55
    And so the pH scale, you're gonna see it
  • 00:00:58
    go from zero all the way to 14
  • 00:01:03
    with of course, seven in the middle,
  • 00:01:06
    and something that is towards the left,
  • 00:01:09
    something that is less than seven is considered acidic,
  • 00:01:13
    and so if you have a pH near zero
  • 00:01:15
    that is highly, highly, highly acidic,
  • 00:01:17
    while something to the right is considered basic
  • 00:01:21
    and something in the middle is considered neutral.
  • 00:01:25
    And another term for basic you'll sometimes see
  • 00:01:28
    is alkaline, and alkaline actually comes from Arabic
  • 00:01:31
    for alkali which was the word that ancient Arab chemists use
  • 00:01:35
    for a compound that happens to be very basic
  • 00:01:39
    by our modern definition.
  • 00:01:42
    But what does it mean to be acidic
  • 00:01:44
    and what does it mean to be basic
  • 00:01:45
    and once again, how does that connect with hydrogen ions?
  • 00:01:49
    Well, it turns out, and I'm not gonna go in depth
  • 00:01:51
    in this video, is that things that are acidic
  • 00:01:54
    tend to have lots of hydrogen ions
  • 00:01:59
    and while things that are basic tend to react,
  • 00:02:03
    react with these hydrogen ions.
  • 00:02:06
    There's other definitions for what it means
  • 00:02:08
    to be an acid or base and we'll go into depth
  • 00:02:10
    in chemistry class on that,
  • 00:02:13
    but this is why it's connected with the term pH.
  • 00:02:17
    Now what are examples of things that are acidic?
  • 00:02:19
    Well, you see it on this chart right over here.
  • 00:02:21
    Here, we're going in the vertical direction.
  • 00:02:23
    Things in our everyday life that are quite acidic,
  • 00:02:26
    a lot of fruits are quite acidic,
  • 00:02:28
    for example, lemons and grapefruits
  • 00:02:30
    and orange juice are quite acidic.
  • 00:02:33
    They're at the low end of the scale.
  • 00:02:34
    And some of the telltale signs for acidity
  • 00:02:37
    is if you were to drink it or eat it,
  • 00:02:39
    that it would have this kind of sharp sour taste to it,
  • 00:02:43
    while if you go to the other end of the spectrum,
  • 00:02:46
    things that are basic, these would be things like bleaches
  • 00:02:49
    and ammonia solution and we can even go
  • 00:02:52
    super basic to liquid drain cleaner,
  • 00:02:55
    and these are going to have more of a slimy texture to it.
  • 00:02:59
    In fact, even soap is quite basic.
  • 00:03:01
    And of the basic things that you could eat,
  • 00:03:03
    you might have a bitter taste associated with it.
  • 00:03:07
    But to be clear, I really don't recommend
  • 00:03:09
    eating or drinking anything that is either highly basic
  • 00:03:13
    or highly acidic, and the reason is
  • 00:03:15
    is that things that are at the extreme of the pH scale,
  • 00:03:19
    so things that are either extremely basic
  • 00:03:22
    or things that are extremely acidic
  • 00:03:26
    like battery acid or hydrochloric acid,
  • 00:03:29
    because they're so reactive, they will damage you.
  • 00:03:32
    If you pour it in your skin, it will damage you.
  • 00:03:34
    If you ingest it, it will damage your cells
  • 00:03:38
    and it can even kill you.
  • 00:03:39
    So don't try to taste things to see
  • 00:03:42
    whether they're acid or basic, and if you do,
  • 00:03:44
    try to make sure that they're closer
  • 00:03:46
    to this middle range of our pH scale.
  • 00:03:50
    So I've talked a lot about things that are acidic
  • 00:03:52
    or basic, but also what's interesting
  • 00:03:54
    is things that we consider to be neutral.
  • 00:03:57
    So our blood, for example, is quite neutral,
  • 00:04:00
    and this is something that doctors might measure
  • 00:04:02
    because if your pH in your blood gets a little bit too high
  • 00:04:05
    or a little bit too low,
  • 00:04:06
    that can cause some serious problems.
  • 00:04:08
    Sea water is pretty close to being neutral.
  • 00:04:11
    Milk is not that far off of being neutral.
  • 00:04:15
    Now with that said, in order to read
  • 00:04:17
    the pH scale appropriately or appreciate the differences
  • 00:04:20
    in acidity and basicity, it's important to realize
  • 00:04:23
    that it is not a linear scale.
  • 00:04:25
    So for example, something that has a pH of eight
  • 00:04:28
    is not twice as basic as something that has a pH of four.
  • 00:04:33
    It turns out, when you go form one level of our pH scale
  • 00:04:35
    to the other, you are going up in basicity,
  • 00:04:39
    say going from a pH four to a pH of five,
  • 00:04:42
    by a factor of 10.
  • 00:04:43
    And so, comparing something with a pH of four
  • 00:04:45
    to a pH of eight, that thing with the pH of four
  • 00:04:47
    would be 10, 100, 1,000,
  • 00:04:51
    10,000 times more acidic,
  • 00:04:53
    or you could say the thing with a pH of eight
  • 00:04:56
    is 10, 100, 1,000,
  • 00:04:58
    10,000 times more basic.
  • 00:05:02
    So I'll leave you there.
  • 00:05:03
    Keep a lookout when people talk about pH balance
  • 00:05:06
    or blood pH, and we're also, as we study
  • 00:05:09
    more and more biology, we're gonna talk about
  • 00:05:11
    how pH might influence some biological reactions
  • 00:05:14
    and especially once you get into chemistry,
  • 00:05:16
    pH will inform us what type of reaction is likely to happen.
Tag
  • pH scale
  • acidity
  • basicity
  • hydrogen ions
  • neutral
  • logarithmic scale
  • biological reactions
  • health
  • chemistry
  • substances