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pH Reminder: Water is held together by ___________________ bonds. These are relatively __________ bonds. These bonds are constantly _________ and _____________. Water molecules can naturally break apart. This is called the dissociation of water.

Acids, Bases and pH One water molecule in 550 million naturally dissociates into a Hydrogen Ion (H+) and a Hydroxide Ion (OH-) Hydrogen Ion Hydroxide Ion Acid Base Acid Base H 2 O  H + + OH -

The pH Scale **Some compounds form acids or bases Scientists use something called the pH scale to measure how acidic or basic a liquid is The scale looks at the concentration of positively charged hydrogen ions (H+) in a solution vs. the amount of negatively charged hydroxide ions (OH-) The scale goes from values 0 through 14. Brain pop

Acids Tastes sour Corrodes metals An acid releases hydrogen ions when it dissolves in water. -High H + concentration -Low OH- concentration - pH less than 7

Bases Tastes bitter, chalky Feels soapy, slippery A base releases hydroxide ions

A B Left to right

Summary! If you have an ionic compound and you put it in water, it will break apart into two ions. If one of those ions is H+, the solution is acidic. If one of the ions is OH-, the solution is basic. There are other ions that make acidic and basic solutions, but we won't be talking about them here.

ACIDBASE

Neutral Pure water contains small, but equal amounts of ions: H+ and OH- On the pH scale the number is 7

Acids vs Bases Acids: Anything that dissolves in water and adds H+. Bases: Anything that dissolves in water and adds OH- ions.

Buffers Buffer - mixtures that can react with acids or bases to prevent major pH changes. Buffered aspirin has a coating on it to prevent the acids in your stomach from dissolving it right away.

Amount of base added Buffering range 452 pH Buffers & Cellular Regulation pH of cells must be kept ~7 pH affects the shape of molecules shape of molecules affects function pH affects cellular function Buffers Control pH donate H+ when [H + ] falls absorb H+ when [H + ] rises Honors Biology