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pH and pOH

Added Apr 13, 2016 •

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this 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 keep seeing references to pH balance everywhere balance soaps and shampoos and deodorant and makeup abound in supermarkets and drug stores and not even see ph balanced water we've talked a lot about balance over the last couple of weeks and pH balance is related to the equilibrium state of a reversible reaction play some Miller 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 weirdly written with a lowercase p in a capital and also what about peaches Alter Ego poh to answer cuz there is no answer the Danish chemist who came up with the term guy with the absolutely amazing names sudden sudden sudden never explained his reasoning some people think that it comes from some form of the word power weather croissants in French or maybe Latin pain this probably differentiating from a reference solution cute but thinking of the p as standing for power does help us remember the meaning more easily he ate part of even easier it stands for hydrogen because hydrogen or protons repay that off to the behavior of acids and bases which is what PH describes basically the power of hydrogen in a solution the strength of the acid or Ray's character of a substance important point of focus if you been watching crash course chemistry from the beginning you gotten the message that water especially in more ways than I can list and pH is just one more of those ways really think of water as 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 go on Earth is that possible explain what the pH of a substance really tells us it's mathematically defined as the negative of the base 10 logarithm of the concentration of hydrogen ions in solution what are those can seem a little bit scary at first but the ones that were using here are super easy and bonus once you get familiar with them here it'll be that much easier to understand I'm in math class turn automatic definition let's do the simplest mathematical definition at any given moment there will be a certain number of hydrogen ions in solution a very small number the concentration will be a number like 1 x 10 to the negative 5th and moles per liter that -5 is your base 10 logarithm take the negative of that and you get the pH 5 my little bit more into the weeds log is the exponent to which another number called the base must be raised to produce the target number 4 base 10 long the base is 10 there what we use most in chemistry and they're really easy to understand and also what we bay scientific notation example launder them of 100 is too because 10 raised to the power of 2 or 10 squared equals 100 Phase 10 logs are so common that we often leave the subscript turn off when we write it like of your calculator has a log button that's just for base 10 logs so what in the name of sauron's and does this have to do with facemelta guess what I'm getting to that turn all starts with Waters crazy potential to act as both an acid and a base random changes in the dining electrical fields around the atoms in water occasionally cause the molly go to break apart from one molecule to another one video plus and hydroxide ions molecules and accept protons in this case it's only interacting with itself but water can interact in the same way with other acids and bases sometimes the hydronium ion written as a simple hydrogen ion H+ allowed reacts to be written with only one water molecule it's not technically accurate but it's close enough to reality that I can be used to simplify things play on concentration we actually mean hydronium ion concentration Association of water is a reversible reaction and in fact the ions always reform into water within a tiny fraction of a second but it's happening all the time instantly in your bottle of water in the water inside yourselves in the ocean all the ways however at any given instant only a tiny number of molecules are dissociated is that the exact number of these molecules is well known to chemists if the equilibrium constant for this reaction and because it's such a special reaction it has its own name the water dissociation constant for KW is equal to 1.0 x 10 to the negative 14 3M constant concentrations of products over concentrations of reactants all raised to the exponent based on the coefficients of the balanced reaction there is however one 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 calculation so the formula for KW become simply the hydronium ion concentration the hydroxide concentration in a water I drown him in hydroxide are formed in a one-to-one ratio so their equilibrium concentrations must be equal X in the concentration of oh H - must equal x as well so the formula for the dissociation constant 1.0 x 10 to the 14th simplifies even further text is X or x squared it's crazy easy the equilibrium concentration of each ion is just the square root of 1.0 x 10 to the negative 14 tell me old calculator in a hell both concentrations equal 1.0 x 10 to the negative 7th moles per liter in equilibrium simply the negative log which is 7 this my friends is the basis of the pH scale water is neutral so 7 is the center of the scale and I can prove it to news with a chemical called litmus is a pH indicator a chemical that turns different colors at different pages there are many different indicators with many different colors but talk more about those next week for now just paper turns pink in acids and bases and a sort of light purple when it's neutral but 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 get slower said such as vinegar were added to the water the concentration of hydronium ion my tries to say 1.0 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 of Base such as ammonia would consume a lot of hydrogen ions if it were added to the water if the hydrogen ion concentration creation drop to 1.0 x 10 to the negative 11th of thousands of equilibrium concentration the pH will be 11 as you can see the logs turn out to be a mathematical lowered hand that saves us from dealing with very huge or very tiny numbers the pH scale then is normally written from 0 to 14 with numbers below 7 representing as it's in numbers Club 7 representing bases it could also go below zero or above 14 but that only happens in super extreme cases that you are very unlikely to encounter I hope acid like Hydrochloric or nitric acid which I and I strongly sometimes even completely that's releasing a lot of protons are called strong acids because they raise the hydrogen stration a lot they also generally have very low PH associate usually have higher pH is generally considered to be like the four to six range strong bases me why like sodium hydroxide consume large amounts of hydrogen ions leaving the concentration hello so they tend to have very high pH of bases like sodium bicarbonate baking soda consume much less in generally have pH technically just 7.0 but in a more practical sense it's usually considered to be between six and eight based on the concentration of hydrogen ion's what about the concentration of hydroxide ions concentration the product of the two concentrations always equals 1.0 x 10 to the negative 14th in any aqueous solution solution of sugar in citric acid in a few other things is 3.2 x 10 to the negative 4th 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 once we can take another step we can find the POA to the solution which is similar to the pH simply the neck Claudio age concentration always 14 in the example we just did pH was 5.4 in the poh was 8.6 and yeah yeah those together play that's only cool to me but that's never stopped me before I love this stuff showing you how to make the pH of the solution song acid or base in it forcible reactions and you learned about the equilibrium constant for that reaction which has a special name the water dissociation constant you learned some examples of acids and bases in New substances as well as why some acids and bases are called strong and others are called weak Hillard 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 learned about some cool mathematical connections between pH and Poh invite you to Gonzales and edited by Blake D pastina with the chemistry consulted was dr. haikal langner it was filmed edited and directed by Nicholas Jenkins the script supervisor was Catherine green Michael Ronda is our sound planographic steam Cafe

Uploaded by Debra Hood.

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pH and pOH

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