The strengths and weaknesses of acids and bases - George Zaidan and Charles Morton

1,024,008 views ・ 2013-10-24

TED-Ed


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Acids and bases are everywhere.
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They're used to make foods,
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soaps and detergents,
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fertilizers,
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explosives,
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dyes,
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plastics,
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pesticides,
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even paper.
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Our stomachs are very acidic.
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Our blood is slightly basic.
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Our proteins are made up of amino acids,
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and the letters in our genetic code,
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those As, Ts, Cs, and Gs,
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are all bases.
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You were probably taught
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how acids and bases behave
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on the molecular level.
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You were probably never taught
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that a long time ago,
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like ancient Greek ago,
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before anyone knew about atoms or molecules,
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acids and bases were defined
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by how they behaved.
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Acids tasted sour and corroded metal.
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Bases felt slippery
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and could somehow counteract acids.
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When molecules dissolved in water interact,
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they are exchanging two main currencies
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with their surroundings:
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protons, also known as hydrogen ions,
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and electrons.
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Depending on how a molecule is composed or shaped,
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it may be willing to donate or accept
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either protons or electrons
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with some other community member.
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And some molecules are far more aggressive than others
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when it comes to donating or accepting either currency.
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Remember that protons are positively charged
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and electrons are negatively charged.
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So, if a molecule is willing to give up a proton,
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that's not too different
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from it being willing to accept an electron --
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either way it's becoming more negatively charged.
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Other molecules are willing to accept a proton
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or give up an electron.
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These are becoming more positively charged.
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Some substances are so aggressive
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about donating their protons
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that when they get a chance,
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all of the molecules in a sample
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will dump a proton,
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sometimes more than one,
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to the surrounding water molecules.
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We call these strong acids.
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Meanwhile, some compounds are so ready
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to accept a proton
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that they won't wait around,
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they'll just rip one off water,
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which usually has two protons
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but is generous enough to hang out with just one.
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We call these strong bases.
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Other acids and bases are not so strong.
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They may donate just a few of their protons to water
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or accept just a few protons from water,
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but most of their molecules stay exactly the same.
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If left alone in water,
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they'll reach some equilibrium point
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where maybe only one out of a hundred
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or one out of ten thousand of their molecules
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has exchanged currency with water.
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As you might guess,
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we label these acids and bases weak,
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but in the common sense of the word,
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they're not weak.
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The vinegar in your salad dressing
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that you can smell from across the room,
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that is a weak acid.
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The ammonia you spray on glass
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for a streak-free shine,
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that is a weak base.
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So, it doesn't take much to be an active player
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in the chemical economy.
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Most acid-base chemistry takes place in water,
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which can act as either an acid or a base,
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accepting deposits and enabling withdrawals
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like a 24-hour molecular ATM.
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And when a proton-deposit customer,
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that's an acid,
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and a proton-withdrawal customer,
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the base,
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shop at the same time,
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their net effect on water's account
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may cancel out,
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and we call this neutralization.
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Now, certain molecules can behave
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as acids or bases without water,
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but that's another story.
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Let's end by saluting water
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as the resilient and fair banker
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for acids and bases.
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It's always open for business,
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doesn't charge interest,
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and will never foreclose on your molecules,
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which is more than I can say for [bleep].
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Waah-waah.
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