Cell Biology. Water, Acids, Bases and Buffers. Water makes up 70-99% of the weight of most living organisms Water

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1 Cell Biology Water, Acids, Bases and Buffers WATER CHEMISTRY Water makes up 70-99% of the weight of most living organisms Water Hydrogen bonded to Oxygen by covalent bond Polar molecule (electrons find oxygen more attractive!) O H H 1

2 Hydrogen Bonding occurs when a covalently bonded hydrogen is attracted to a negatively charged atom some distance away. represented by because it is a weak bond bond breaks easily Water as a. 1. Universal Solvent Other polar (charged) molecules dissolve in it e.g. NaCl (salt) added to water + ve hydrogen ions in water attract to - ve chlorine ions of salt These attractions result in sodium and chloride separating and thus dissociate into the water NaCl is hydrophyllic 2

3 Water as a. 2. Temperature Regulator Temp of liquid water and s slowly Hydrogen bonds in water help it resist temp changes b/c a great deal of energy must be added or lost to raise or lower the temp. High heat of vaporization What are the benefits of this? 3. Lubricant Water molecules cling (cohesive) together because of H- bonds YET it flows freely as a fluid = good medium for transporting dissolved and suspended particles. Blood is 92% water You should be able to.. Answer these questions: 1. What holds water molecules together? 2. Why is water so important to living things? 3. What is a solvent? 4. Why is the solvent, water so important to living things? 3

4 ACIDS, BASES and BUFFERS - When water dissociates, an equal number of ions and HYDROGEN IONS and HYDROXIDE IONS are released: H 2 O H + + OH - If the # of H + ions is not equal to the number of OH - ions than the solution has become either acidic or basic ACIDS Eg. Lemon, vinegar, coffee,. etc Sour taste Changes litmus from BLUE to RED Molecules that dissociate (break-up) and release hydrogen ions (H + ) Proton (H + ) DONORS Acid solutions have more H + ions than OH - ions Eg. HCl (strong acid): HCl à H + + Cl - HCl + H 2 O H 3 O + + Cl proton proton hydronium ion donor acceptor (acid) (base) 4

5 BASES Eg. Baking soda, Milk of Magnesia, ammonia. etc Human blood is slightly basic! Bitter taste Changes litmus from RED to BLUE Molecules that release hydroxide ions (OH - ) or take up hydrogen ions (H + ) Proton (H + ) ACCEPTORS Basic solutions have more OH - ions than H + ions Eg. NaOH (strong base): NaOH à Na + + OH - ph and the ph SCALE Measure of the relative acidity or alkalinity of a solution Scale is logarithmic A difference of one ph unit represents a tenfold change E.g. a ph of 5 is 10x greater than a sample with a ph of 6 and 100X greater than a ph of 7 5

6 [Hydrogen ion] and ph are inversely related: The higher the [H + ] the LOWER the ph The lower the [H + ] the HIGHER the ph BUFFERS Compounds that neutralize fluctuating ph levels Can be a compound or a combination of compounds Often a weak acid or base and a related salt Resist changes by soaking up H + ions or OH - ions Eventually will run out 6

7 Carbonic Acid (H 2 CO 3 ) - Bicarbonate (HCO 3- ) Buffering System Used to maintain a mammalian blood ph of 7.4 Dissociation and reformation of carbonic acid: When OH - ions are added to blood, the following reaction counteracts any changes to the blood ph: When H + ions are added to blood, the following reaction prevents significant changes to blood ph: HEMOGLOBIN as a buffer During Exercise: Muscles use up oxygen (from Hemoglobin) Glucose is broken down and CO2 and H+ is produced removed from muscle by blood and carried by hemoglobin If amount of CO2 and H+ exceeds the capacity of hemoglobin Than ph of blood is lowered (=acidosis) Lungs and kidneys respond to ph changes by removing C)2, HCO3- and H+ from blood (Please Refer to Figure on next slide) 7

8 Practice Questions: 1. What happens to the concentration of hydrogen ions in a beaker of pure water when an acid is added to it? 2. What would the ph of water be BEFORE the addition of an acid? 3. What happens to the ph of the solution as you add an acid to it? 4. If you begin with pure water and add an acid until the solution has a ph of 4, how many more times acidic is the new solution compared to the pure water? 8

9 Practice Questions: ANSWERS 1. The concentration of H + increases as acid is added to pure water. 2. Water is neutral and has a ph of The ph of the solution will continue to decrease as you add acid to it. Acids have a ph of less than 7. The lower the number, the stronger the acid. 4. If you begin with pure water and add an acid until the solution has a ph of 4, how many more times acidic is the new solution compared to the pure water? 9