Acid Base Notes
pH Scale
Forms H + ions in solution Corrosive Tastes Sour What is an Acid? Acid: pH less than 7 Neutralizes bases Forms H + ions in solution Corrosive Tastes Sour Add to your venn diagram
Dissolves fats and oils Usually forms OH- ions in solution What is a Base? Base: pH greater than 7 Feels slippery Dissolves fats and oils Usually forms OH- ions in solution Neutralizes acids Commonly used as cleaning products Tastes Bitter
pH This is molarity pH = -log [H+] Increase of H+ ions. Scale of 10’s. Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 285
HCl(aq) + H2O(l) H3O+(aq) + Cl- Acids and Bases There are several definitions for Acids and Bases; the most common is the Brønsted-Lowry definition: Acids are proton (H+) donators. Bases are proton (H+) acceptors. Loses a proton Nature of science: Changes over time. Gains a proton HCl(aq) + H2O(l) H3O+(aq) + Cl-
Nature of Science Curiosity leads us to use chemicals in new ways in an attempt to improve our lives. How can we use acids and bases to make our lives better?
Effects and Uses of Acids and Bases Acids and bases occur naturally in ecosystems of all types. Our stomachs produce acids for digestion. Certain animal and plant cells must be acidic or basic so that proteins function best. Soils may be basic or acidic determining what types of plants can thrive there. Water may also be acidic or basic, influencing what types of fish can live in the environment. Changing the natural pH can destroy the environments that are affected.
Digestion and pH Mouth-pH around 7. Saliva contains amylase, an enzyme which begins to break carbohydrates into sugars. Stomach- pH around 2. Proteins are broken down into amino acids by the enzyme pepsin. Small intestine-pH around 8. Most digestion ends. Small molecules move to bloodstream toward cells that use them. Why must pH be neutral in the small intestine?
Buffered Solutions The pH of blood must be kept in within a narrow range. Buffers are solutions that resist changes in pH when limited amounts of acid or base are added. Buffer solutions are necessary to keep the correct pH for enzymes in many organisms to work. Many enzymes work only under very precise conditions; if the pH moves outside of a narrow range, the enzymes slow or stop working and can denature.
pH paper pH paper changes color to indicate a specific pH value.
Indicators Chemical dyes whose color are affected by acidic and basic solutions are called indicators. Not all indicators show when the pH is 7.
Indicators The following table can be used to see when each indicator should be used:
Natural Indicators There are some natural indicators such as cabbage juice or hydrangeas.
How do we measure concentration in Chemistry? In Chemistry we call concentration: Molarity. What do you notice about the word molarity? The units for molarity are moles per liter. Molarity is a measure of how much solute is in the solvent.
We can calculate the molarity using the following equation: (It is on your periodic table)
What is the molarity 0.256 moles of NaCl in 0.50 liters of water? Molarity Practice What is the molarity if you have a solution that has 0.02 moles NaCl in 1 liter of water? What is the molarity 0.256 moles of NaCl in 0.50 liters of water?
Safety: Neutralization Lab Always wear safety goggles, lab apron, and gloves. Dispose of used litmus paper into “Waste” beakers on counters. HCl, H2SO4, and CHOOH are corrosive to skin and clothing. HCl, H2SO4, and CHOOH are toxic. NaOH, NH4OH, are caustic and toxic. Ca(OH)2 is an irritant (skin, eyes, etc)
Reactions Between Acids and Bases A neutralization reaction is a reaction in which an acid and a base in an aqueous solution react to produce salt and water. A salt is an ionic compound made up of a cation from a base and an anion from an acid. Composed of the negative ion of an acid and the positive ion of a base.
Reactions Between Acids and Bases (cont.) A neutralization reaction is the reaction of an acid with a base to produce salt and water. HCl + NaOH NaCl + H2O 2 NaOH + H2SO4 2 H2O + Na2SO4