General Chemistry Spring 2013 ACIDS AND BASES UNIT 10 General Chemistry Spring 2013

The Importance Of acids… Blood is controlled by buffers Citrus fruits (citric acid) Vinegar (acetic acid) Vitamin C (ascorbic acid) Aspirin (acetyl salicylic acid) Car batteries (sulfuric acid)

The Importance Of bases… Baking soda Milk of magnesia Antacids have carbonates, bicarbonates and hydroxides to neutralize acids Ammonia (cleaning products) Sodium hydroxide, aka: lye (oven and drain cleaner)

Dangers of acids and bases

Resources Dangers of sodium hydroxide Chemical Burn Coke Cans Dangers of Coke and Pepsi

How do you know you have… An acid? Produces H+ in water Blue litmus paper turns red Sour taste Reacts on metal pH less than 7 Metal etched using acid

How do you know you have… A base? Produces OH- ions in water (hydroxide ions) Red litmus paper turns blue Slippery feel Bitter taste (taste shampoo tomorrow morning) pH higher than 7

pH Means “potency of hydrogen”

The pH Scale

Arrhenius Acids Substance that ionizes in water to produce hydrogen ions (H+) “ionization”- process by which covalent compounds form cations and anions Ex) HCl  H+ + Cl-

Arrhenius Base Substance that dissociates in water to release hydroxide ions (OH-) “dissociation”- process by which ionic compounds separate into ions Ex) NaOH  Na+ + OH-

Neutralization Reactions An acid neutralizes a base to yield a salt and water. Example A) Hydrochloric acid reacts with sodium hydroxide to give the salt sodium chloride and water. HCl + NaOH  NaCl + H2O Different acids yield different salts, but water is always a product When you mix an acid and base, you reach an equivalence point (when the # moles of H+ = # moles of OH-)

Neutralization Reactions Example B) H2SO4 + 2 NaOH  Na2SO4 + 2 H2O The hydrogen ion (H+) from the acid is neutralized by the hydroxide (OH-) ion from the base. These two ions combine to form water.

Identifying an Acid and Base Each salt is composed of the cation (+) from the reacting base and the anion (-) from the acid. Predict the acid and base that produce the following salts: Potassium acetate, KC2H3O2 Let’s see some steps first.

Predicting Acids and Bases Split the salt and water (HOH) formula into ions Which ion gets H+? Write the formula Which ion gets OH-? Write the formula Potassium acetate, KC2H3O2 KOH + HC2H3O2  KC2H3O2 + HOH OPPOSITES ATTRACT!

Predicting Acids and Bases Lithium fluoride, LiF HF + LiOH  Li F + H2O

The pH Scale Revisited What is pH again? It expresses the acidity of a solution; the concentration of hydrogen ions Ranges from… 0  14 As pH decreases, the concentration of hydrogen ions increases, and the concentration of hydroxide ions decreases. In a neutral solution, the concentration of hydroxide ions and hydrogen ions are equal.

Acid-Base Indicators Methyl Red Color change ~pH 5 Below pH 5: red Above pH 5: yellow At 5? Orange (only a portion has been converted from yellow to red)

Acid-Base Indicators Bromthymol blue Color change ~pH 7 Below pH 7: yellow Above pH 7: blue At 7: greenish Good test for CO2 in lungs

Acid-Base Indicators Phenolphthalein Color change ~ pH 9 Below pH 9: colorless Above pH 9: pink At pH 9: very light pink