Raw materials and fuel for our bodies Chapter 2: Chemistry Raw materials and fuel for our bodies Lectures by Mark Manteuffel, St. Louis Community College

Do Now: Place homework (worksheet & summary) on your desk. ON a scrap piece of paper answer the following questions: Chlorine-35+ Is this atom an ion or an isotope? How do you know? What is the Atomic number, atomic mass, and how many protons, neutrons, and electrons does it have? 2. Tell me why hydrogen bonding is essential life on earth.

2.6 Living systems are highly sensitive to acidic and basic conditions. What are acids and bases? Ask students – what do you think of whene we say “acids” – list examples. Bases? 3

Hydrogen Ions and Hydroxide Ions OH - H2O O O H H H H20 dissociates into H+ and OH- in equilibrium. Meaning the number of water molecules that dissociates remains constant. Until you add an acid (H+) or a base (OH-) and the equation shifts to the right There’s a lot more going on in water than meets the eye. Most of the molecules are H2O, but at any instant some of them break up into two parts: H+ and OH. In pure water, the amount of H+ and OH must be exactly the same, since every time a molecule splits, one of each is produced. But in some fluids containing other dissolved materials, the fluid can have more H+ or more OH. Ionized Hydroxide Molecule Non-Ionized Water Molecule 4

pH Scale The amount of H+ in a solution is a measure of its acidity and is called pH. Acids Bases Basic = alkaline The amount of H+ or OH in a fluid gives it some important properties. In particular, the amount of H+ in a solution is a measure of its acidity and is called pH. The more free hydrogen ions floating around, the more acidic the solution is. Pure water is in the middle of the pH scale, with a pH of 7.0. Any fluid with a pH below 7.0 has more H+ ions (and fewer OH ions) and is considered an acid. Any fluid with a pH above 7.0 has fewer H+ ions (and more OH ions) and is considered a base. 5

Figure 2-18 pH is a measure of acidity. The pH scale is logarithmic, like the Richter Scale for earthquakes: an increase in 1 on the scale represents a ten-fold increase in the hydrogen ion concentration. An decrease of 2 represents a hundred-fold increase in hydrogen ion concentration. This means that Coke, with a pH of about 3.0, is 10,000 times (!) more acidic than a glass of water, with a pH of 7.0. 6

H+ Ions and Acids Low pH More H+ than OH- H+ very reactive Acids can donate H+ to other chemicals Stomach acids Solution is acid if H+ is in excees H+ ions are essentially free-floating protons. Acids can donate their H+ ions to other chemicals. In fact, H+ is a very reactive little ion. Its presence gives acids some unique properties. For instance, the hydrogen ions in acids can bind with atoms in metals, causing them to corrode. That’s why you can dissolve nails by dumping them in a bucket of acid (or Coke). Your stomach produces large amounts of hydrochloric acid (HCl) and has a pH between 1 and 3 (HCl is acidic because most of the hydrogen ions split off from the chlorine raising the H+ concentration of the fluid). The acid in your stomach helps to kill most bacteria that you ingest. It also enhances greatly the breakdown of the chemicals in the food you eat and the efficiency of digestion and absorption.

Bases High pH Low H+ /High OH Reactive Antacids Cleaning materials (soap, detergent) Baking soda, seltzer, milk of magnesia Solution is basic if OH- is in excess. Bases have very low concentrations of H+ and relatively high concentrations of OH. Baking soda is a common basic substance. Some bases are called antacids because the OH ions in bases can bind with excess H+ ions in acidic solutions, neutralizing the acid. Base-containing products such as Alka-Seltzer and milk of magnesia reduce the unpleasant feeling of heartburn and acid indigestion that sometimes arise from the overproduction of acids by the stomach. Bases are commonly used in household cleaning and generally have a bitter taste and a soapy, slippery feel to them.

Blood pH Buffers can quickly absorb excess H+ ions to keep a solution from becoming too acidic can quickly release H+ ions to counteract any increases in OH concentration The pH of blood is usually 7.4. Given that most cellular reactions produce or consume H+ molecules, there ought to be great swings in the pH of our blood. Unfortunately, our bodies can’t tolerate such swings. Most of the chemicals that aid in the chemical reactions within our blood or cells stop functioning well if the pH swings by less than half a point. Fortunately there are some chemicals that act like bank accounts for H+ ions. Called buffers, these chemicals can quickly absorb excess H+ ions to keep a solution from becoming too acidic and they can quickly release H+ ions to counteract any increases in OH concentration. Buffers can be like a bank – absorbs H+ when too acidic and release H+ when too basic. 9

Exit Slip What is pH measuring? How many more times acidic is coke (pH 3) than coffee (pH 5)? Than blood (pH 7)? Than Sodium Hydroxide (NaOH, pH 14)? Coke is 100 times acidic as coffee. Coke is 10,000 times acidic as blood. Coke is 100,000,000,000 times acidic as NaOH