Biochemistry Water and the Fitness of the Environment Concept: Acidic and Basic condi9ons affect living organisms

Transcription

1 Biochemistry Water and the Fitness of the Environment Concept: Acidic and Basic condi9ons affect living organisms

2 Objec&ves: SWBAT calculate the ph of a substance and explain how it would change with the addi&on of an acid or base. 2

3 KP3: Hydrogen atoms in water molecules constantly bounce among one another ACIDIC AND BASIC CONDITIONS AFFECT LIVING ORGANISMS A bonded hydrogen atom within a water molecule can shift between two water molecules (from one molecule to the other). 3

4 KP3: Hydrogen atoms in water molecules constantly bounce among one another The hydrogen atom leaves its electron behind and is transferred as a proton, or hydrogen ion (H + ) The molecule with the extra proton is now a hydronium ion (H 3 O + ), though it is often represented as H + The molecule that lost the proton is now a hydroxide ion (OH ) 4

5 Acids, Bases and Buffers. Though statistically rare, the dissociation of water molecules has a great effect on organisms About 2 in every billion water molecules exist as H + and OH Changes in concentrations of H + and OH can drastically affect the chemistry of a cell 5

6 Acids, Bases and Buffers. Concentrations of H + and OH are equal in pure water Adding certain solutes, called acids and bases, modifies the concentrations of H + and OH Biologists use something called the ph scale to describe whether a solution is acidic or basic (the opposite of acidic; also known as alkaline) 6

7 Acids, Bases and Buffers. Simply put, An acid is any substance that increases the H + concentration of a solution A base is any substance that reduces the H + concentration of a solution Bleach 7

8 Acids, Bases and Buffers. Buffers The internal ph of most living cells must remain close to ph 7 Buffers are substances that RESIST changes in concentrations of H + and OH in a solution, therefore they RESIST a change in ph Most buffers consist of an acid-base pair that reversibly combines with H + 8

9 Buffers Buffers have many important biological functions. They keep a solution at a constant ph, when manageable amounts of acid of base are added. Ex: Your blood is a buffer! Its ph is very slightly basic at 7.4. Even though you may eat many different types of foods or medicines, your blood ph stays rela&vely stable, varying only about 0.1. That means your blood controls its own ph!

10 Buffers Buffers contain ions or molecules that react with hydronium or hydroxide if they are added to the solution. That means, even if you add an acid or a base, your ph will stay the same. To make a buffer, you combine a weak acid or a weak base with its corresponding salt.

11 Buffers Example: Ammonia is combined with its salt, NH 4 Cl, in sol n: If acid is added to this solution, ammonia reacts with the H + : NH 3 (aq) + H + (aq) NH 4 + (aq) If a base is added to this solution, the NH 4 + from the dissolved salt will react with the OH - : NH 4 + (aq) + OH - (aq) NH 3 (aq) + H 2 O (l)

12 Buffers Blood s ph is regulated by many systems, but dissolved CO 2 is a very important method. Carbonic acid, H 2 CO 3, and the hydrogen carbonate ion, HCO 3-, are both dissolved in your blood. CO 2 (g) + H 2 O (l) H 2 CO 3 (aq) If you add OH - : H 2 CO 3 (aq) + OH - HCO 3 - (aq) + H 2 O (l) If you add H + : HCO 3 - (aq) + H + H 2 CO 3 (aq)

13 Buffers Your lungs control the amount of carbon dioxide in your body. If your body takes in too much carbon dioxide, your blood may become too acidic so you may yawn to lower the concentration of carbonic acid by expelling CO 2.

14 Buffers If you hyperventilate, too much CO 2 is expelled, which causes the concentration of carbonic acid to become too low, and your blood may become too basic. Breathing into a paper bag will increase the concentration of CO 2 in your lungs and restore the proper ph.

15 Buffers in Ac&on Acidification: A Threat to Water Quality Human activities such as burning fossil fuels threaten water quality CO 2 is the main product of fossil fuel combustion About 25% of human-generated CO 2 is absorbed by the oceans CO 2 dissolved in sea water forms carbonic acid; this process is called ocean acidification 15

16 Buffers in Ac&on As seawater acidifies, H + ions combine with carbonate ions to produce bicarbonate Carbonate is required for calcification (production of calcium carbonate) by many marine organisms, including reef-building corals 16

17 Acid Rain The burning of fossil fuels is also a major source of sulfur oxides (SO x ) and nitrogen oxides (NO x ) These socks and knocks compounds react with water in the air to form strong acids that fall within rain or snow Acid precipitation is rain, fog, or snow with a ph lower than 5.2 Acid precipitation damages life in lakes and streams and changes soil chemistry on land 17

18 Acid Rain: Before & AJer 18

19 KP4: ph measures the H+ concentra&on on a logarithmic scale. Low = acidic. An acid is any substance that increases the H + concentration of a solution A base is any substance that reduces the H + concentration of a solution The scale was designed to compare WEAK acids and bases. 19

20 KP4: ph measures the H+ concentra&on on a logarithmic scale. Low = acidic. In any aqueous solution at 25 C the product of H + and OH is constant and can be written as the autoionization constant of water [H + ][OH ] = The ph of a solution is defined by the negative logarithm of H + concentration, written as ph = log [H + ] For a neutral aqueous solution, [H + ] is 10 7, so ph = ( 7) = 7 20

21 The ph Scale Acidic solutions have ph values less than 7 Basic solutions have ph values greater than 7 Most biological fluids have ph values in the range of 6 to 8 21

22 Whiteboards What is A pointing to? A B 22

23 Whiteboards What is B pointing to? A B 23

24 Whiteboards How does A cause ice to float? A B 24

25 Whiteboards How does B cause water to be a good solvent? A B 25

26 Whiteboards Which (A or B) helps water molecules cohere with one another? A B 26

27 Whiteboards Which (A or B) is responsible for water s high surface tension? A B 27

28 Whiteboards HARD: Draw the Lewis Dot Structure for water. A B 28

29 Whiteboards How many times more basic is tomato juice (ph 4) than battery acid (ph 1)? 29

30 Whiteboards What is the ph of a 0.35M solution of H+? 30

31 Whiteboards Ammonia (ph 11) is times more than rainwater (ph 5) This ques&on deals with the concept of ph: acids and bases. The ph scale is a logarithmic scale that measures how much acidity or basicity a solu&on contains. A ph of 4 is 10 &mes more acidic than a ph of 5. A ph of 6 is 10 2 or 100 &mes more basic than a ph of 4, and so on. Therefore a ph of 10 is 103 or 1000 &mes more basic than a ph of 7. 31

32 Independent Prac&ce (Quiz Handout on proper&es of water) 32