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Crash Course Chemistry pH and pOH

Added May 07, 2019 •

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This video is one of a series of videos that address different key concepts from chemistry. This video discusses the applications of pH and pOH.

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where's may come as a bit of a shock to you but I'm not super into personal grooming like I understand soap and shampoo but there is all this other stuff now and I keep seeing references to pH balance everywhere pH balance add deodorant and makeup abound in supermarkets and drugstores and I've even seen ph balanced water over the last couple of weeks and pH balance is related to the equilibrium state of a reversible reaction familiar with the pH scale and you know that it has to do with acids and bases but what is pH exactly and why is it with a lowercase p in a capital H and also what about pH is Alter Ego probably easiest to answer cuz there is no answer no one really knows what the pay is the Danish chemist who came up with the never explain his reasoning some people think that it comes from some form of the word of power weather croissants in French or maybe a Latin pondis solution standing for power does help us remember the meaning easily even easier for hydrogen because hydrogen or protons are pivotal to the behavior of acids and bases which is what PH describes in the solution the strength of the acid or is character of a substance revolves around one very important point of focus our old friend water if you've been watching crash course chemistry from the beginning you gotten the message that water is special in more ways than I can list and pH is just one more of those ways we think of when there is a perfectly neutral substance neither acidic nor basic and that's true but as I've mentioned before water can also function as an acid releasing hydrogen ions also known as protons and as a base consuming them is that possible explain we first have to understand what the pH of a sub really tells us how chemically we say the pH represents the power of hydrogen in the solution it's mathematically defined as the negative of the base 10 logarithm of the concentration of hydrogen ions in solution okay so now that you're terrified I'm here to help a little bit scary at first but the ones that were using here are super easy and bonus plays mathematical definition certain number of hydrogen ions in solution a very small number the concentration will be in like 1 x 10 to the negative of that and you get the ph5 how to get a bit more into the weeds logarithm of a number is the exponent to which another number called the base must be raised to produce the target number is 10 we use most in chemistry they're really easy to understand and also what we've a scientific notation on the base 10 logarithm of 100 is too because 10 raised to the power of 2 or 10 squared equals 100, that we often leave the subscript turn off when we write it like on your calculator has a log button that's just for base 10 log so what is crazy potential to act as both an acid and a base what is in the dining light circle fields around the atoms in water occasionally cause them to break apart to another one forming a hydronium ion a plus and a hydroxide ion 08 - the base release and accept protons in this case it's only interacting with itself but water can interact in the same way with other acids and base sometimes you see the hydronium ion written as a simple hydrogen ion H+ allowing the reaction to be written with only one water molecule things when we say that the pH is the negative log of the Hide stration Yeah we actually mean hydronium ion concentration really sign just got a little bit wrong and personal reaction and in fact the ions always reform into water within a tiny fraction of a second but it's happening all the time constantly in your bottle of water in the water inside your cells and in the ocean all the ways however at any given instant only a tiny number of molecules are dissociated in in fact the exact number of these molecules is well-known to chemists is the equilibrium constant for this reaction and because it's such a special reaction that has its own name the water dissociation constant kwkw is equal to 1.0 x 10 to the negative 14th the formula for KW is set up like any equilibrium constant concentrations of products over concentrations of reactants all raised to the exponents based on the coefficient of the balanced reaction there is a difference because the ions represent such a tiny proportion of the total mass the water itself is essentially pure and pure substances because they don't have concentrations aren't included in equilibrium calculations for KW become simply the hydro concentration of hydroxide concentration according to the balanced equation for the dissociation of hydronium and hydroxide are formed in a one-to-one ratio so their equilibrium concentrations must be a means of the concentration of h3o + 4 exam X4 the concentration of 08 - must equal x as well so the formula for the dissociation constant 1.0 * 10 * X or x squared Suddenly It's Crazy easy the equilibrium constant the square root of 1.0 times 10 to the negative Librium the pH then is simply the negative log that which is seven friends is the basis of the pH scale is neutral so 7 is the center of the scale is a pH indicator a chemical that turns different colors at different pH is there aren't many different indicators with many different colors but we'll talk more about those next week and a sort of light purple when it's neutral one thing you need to remember about the pH scale does pH is calculated from a negative logarithm it turns everything backward when the hydrogen ion concentration goes up the pH gets lower concentration of hydronium ion my tries to say 1 points x 10 to the negative 4th moles per liter which is a thousand times more than before that concentration would push the PH down to four on the other hand the base of hydrogen ions if it were out of the water hit the hydrogen ion concentration dropped to 1.0 x 10 to the negative 11th a thousandth of the equilibrium concentration the pH will be 11 as you can see the longest turn out to be a mathematical shorthand that saves us from dealing with a very huge you're very tiny numbers is normally written from 0 to 14 with numbers below represent faces that you watched very unlikely to encounter Italy I hope acid like Hydrochloric or nitric acid which I strongly sometimes even completely that's a lot of protons are called because they have very low ph is associate are completely releasing much smaller. They usually have higher pH is generally considered to be in like the 4 to 6 range in large amounts of hydrogen ions leaving concentrations so they tend to have very high peaches this is like sodium bicarbonate baking soda consumed more practical sense if usually considered to be between 6 and a pH is based on the concentration of hydrogen hydronium ion concentration of hydroxide ions calculate the Poh the negative log the Hydra High concentration easy because KW never changes the concentrations of hydrogen and hydroxide are only equal in pure water or perfectly neutral Solutions the product of the two concentrations equals 1.0 times and to the negative 14th in any aqueous solution solution of sugar in citric acid in a few other things for leader just for the fun of it let's go ahead and calculate the pH is at that point which turns out to be 3.5 but we can also use the KW in the hydronium ion concentration to do a very simple division problem and find the hydroxide concentration it works out to 3.1 x 10 to the negative 11th moles per liter another step we can find the poh of the solution which is similar to the pH simply the negative log of the o h concentration corndog some of the ph and the poh is always 14 in the example we just did. Was 5.4 in the PO it was 8.6 and yeah I never stopped me before I love this. bend your mind by showing you how to make the pH of the solution Hold Steady even if you dump a strong acid or base in it to me has to form hydronium and hydroxide ions in possible reactions have you learned about the equilibrium constant for that reaction which has a special name the water dissociation constant you learned at some examples of acids and bases and neutral substances as well as why some acids and bases are called strong and others are called we killing about logarithms and how you can use them to calculate the pH of a substance and a little bit about poh which can be calculated with logarithms also with subtraction and finally you and about some cool mathematical connections between pH and Poh Pasadena the chemistry consulted with Doctor Hico liner it was filmed edited then directed by Nicholas Jenkins descriptive revisor was Katherine green designer and a graphics team

Uploaded by Debra Hood.

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Crash Course Chemistry pH and pOH

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