Acids, Bases, and Salts Chapter 23 sections 1-3

Acids, Bases, and Salts Section 1 Acids & Bases slides 3-18 Section 2 Strength of Acids & Bases slides 19-29 Section 3 Salts slides 30-46

1- Acids and Bases What You’ll Learn: How acids & bases are similar & different Formulas and uses of common acids and bases

Acids An acid is a substance that produces hydrogen ions, H+, in a water solution. The ability to produce these ions that gives acids their characteristic properties. A hydronium ion, H3O+ , is a combination of an H+ ion & a water molecule.

Properties of Acids Taste sour, BUT DON’T TASTE Some can burn you Are corrosive, can eat away metal Cause indicators to change color

Indicator An organic compound that changes color in acid and base. Litmus paper is an indicator that turns red in acids.

What are some common acids? Many foods contain acids: Citrus fruits, Lactic acid in yogurt & buttermilk Pickled foods contain vinegar or acetic acid Your stomach contains hydrochloric acid to help digest food

Common Acids & Their Uses Name Use Other Info Acetic Acid Food preservation & preparation In solution w/ water= vinegar Acetylsalicylic Pain & fever relief Known as aspirin Ascorbic acid Antioxidant, vitamin Vitamin C Carbonic acid Carbonated drinks Cave formation, acid rain Hydrochloric Gastric juice; steel cleaner Muriatic acid Nitric acid To make fertilizers Colorless yet yellows when light exposed Phosphoric To make detergents, fertilizers & other chemicals Slightly sour taste; detergents cause water pollution Sulfuric acid Car batteries, to make fertilizers, etc. Dehydrating agent, causes burns

Bases A base is any substance that forms hydroxide ions, OH-, in a water solution. A base is also any substance that accepts H+ ions from acids. Unlike acids, not many foods are bases- egg whites, baking powder & medicinal antacids. Soap is basic; characteristic slippery

Bases Many cleaning products contain bases. Used in industry- NaOH used to separate cellulose fibers from wood pulp to make paper.

What are the properties of bases? Bases are the opposite of acids. When not dissolved in water, many are solids in the form of crystals. In solution, they feel slippery and taste bitter. Like strong acids, strong bases are corrosive & can burn you.

What are the properties of bases? NEVER taste or touch a substance to see if it’s basic. Bases also cause indicators to change color. Litmus paper is an indicator that turns blue in bases.

What are some common bases? Aluminum hydroxide Color-fast fabrics, antacid, water purification Sticky gel that collects suspended clay & dirt particles on its surface Calcium hydroxide Leather-making, mortar & plaster, lessen acidity of soil Called caustic lime Magnesium hydroxide Laxative, antacid Called milk of magnesia when in water Sodium hydroxide To make soap, oven cleaner, drain cleaner, textiles, paper Called lye & caustic soda, exothermic when added to water Ammonia Cleaners, fertilizer, to make rayon & nylon Irritating odor that damages nasal passages & lungs

Solutions of Acids & Bases Water is the main solvent for acid and base products because water has polarity. Remember, polarity means a molecule has a slightly negative end & a slightly positive end.

What happens when acids dissolve in water? The negative ends of nearby water molecules attract the positive hydrogen in the acid. The acid separates into ions, which is called dissociation. The H+ ions combine with the water molecules to form hydronium ions (H3O+).

What happens when acids dissolve in water? +  + HCl + H2O  H30+ + Cl-

What happens when bases dissolve in water? Bases form hydroxide ions (OH-) in water. Positive ends of nearby water molecules attract the hydroxide ions in the base which do not combine with water molecules.

How is ammonia different from other bases? Ammonia is a base that does not contain –OH. In water, ammonia actually dissociates water molecules to form an ammonium ion, NH4+. You should NEVER use products containing ammonia with other cleaners containing chlorine. They react producing toxic gases.

2- Strength of Acids and Bases What You’ll Learn: What makes acids & bases strong or weak How strength and concentration are alike and different

Strong & Weak Acids & Bases The strength of an acid or a base depends on how many acid molecules dissociate into ions in water. In a strong acid almost all acid molecules dissociate in water. Examples include hydrochloric acid (HCl), nitric acid (HNO3), and sulfuric acid (H2SO4).

Strong & Weak Acids & Bases In a weak acid only a small number of acid molecules dissociate in water. Examples include acetic acid (CH3COOH), and carbonic acid (H2CO3). Acetic acid is used to preserve pickles.

How do you write chemical equations for acid dissociation? An equation for the dissociation of a strong acid uses a single arrow hat points toward the ions that form. HCl (g) + H2O(l)  H3O+(aq) + Cl-(aq) In weak acids an equation uses double arrows pointing in opposite directions. CH3COOH(l)+H2 H3O(aq)+CH3COO-

How are strength and concentration described? Strong & weak refer to how easy it is for the acid or base to dissociate in solution. Strong acids & bases dissociate completely while weak acids & bases only partially dissociate. Dilute & concentrated tell how much acid or base is dissolved in the solution (few or many).

pH of a Solution The pH of a solution is a measure of the concentration of H+ ions in the solution. The scale ranges from 0 to 14 with the greater the concentration of H+ ions, the lower on the scale and the more acidic it is.

pH scale

pH scale Solns with a pH lower than 7 are acidic or with a pH greater than 7 are basic. Solns with a pH of 7 are called neutral & have equal conc. of H+ & OH- ions. Pure water at 25°C has a pH of 7. Universal indicator paper changes color when ions are present. A pH meter uses electrodes to determine pH.

pH scale

Why is pH of blood important? The pH of your blood must remain between 7.0 & 7.8 in order for enzymes to work. Enzymes are protein molecules that act as catalysts for many of your body’s reactions. Buffers are solutions containing ions that react with acids or bases to decrease their effects on pH.

Why is pH of blood important? Buffers are solutions containing ions that react with acids or bases to decrease their effects on pH. Buffers help your blood stay at an almost constant pH of 7.4. One buffer system in the blood involves bicarbonate ions, HCO3-.

3- Salts What You’ll Learn: Identify a neutralization reaction About salt and how it forms About soaps and detergents

Neutralization Neutralization is a chemical reaction between an acid & a base that happens in a water solution. NaOH neutralizes HCl. Hydronium ions from the acid combine with OH- from the base producing neutral water. HCl + NaHCO3 2H2O

Neutralization Antacids are medicines that contain bases or other compounds that neutralize the HCl in your stomach. One of these antacids is sodium bicarbonate- NaHCO3. HCl + NAHCO3NaCl + CO2+H2O

How is salt formed? HCl is neutralized by NaOH but only half the ions are shown. The other ions react to form a salt. A salt is a compound formed when the negative ions from an acid combine with the positive ions from a base. Na++ Cl-  NaCl

How do acid-base equations look? Acid + base  salt + water The equation for the reaction between HCl and NaOH is: HCl + NaOH  NaCl + H2O

Salts Salt is necessary for many organisms. Most salts are made of a positive metal ion & a negative ion such as Cl or CO3. Ammonium salts contain NH4 instead of a metal.

Some Common Salts Name, Formula Common Name Uses Sodium chloride, NaCl Food, making chemicals Sodium hydrogen carbon Sodium bicarbonate baking soda Food, antacids Potassium nitrate, KNO3 saltpeter fertilizers Ammonium chloride Sal ammoniac Dry-cell batteries

Titration In titration, a solution of known concentration is used to find the concentration of another solution. Measure the volume of the solution of unknown concentration. Add a few drops of phenolphthalein, a colorless indicator that turns pink in a base & stays pink when the acid is neutralized.

Titration Since the unknown is an acid, slowly & carefully add a base solution of known concentration drop by drop until one drop turns the solution pink and the color stays. The completed titration is the endpoint. The acid is neutralized. Use the volume of the base that was added to calculate the concentration of the acid solution.

What are indicators? Many natural substances are acid-base indicators. The indicator litmus comes from a combination of a fungus and a algae called lichen. The flowers of the hydrangea plant are indicators, pink in basic soil & blue in acidic soil. Red cabbage juice is also an indicator- deep red at pH 1, lavender at pH 7, & yellow-green at pH 10.

Soaps and Detergents Soaps are organic salts with a nonpolar organic chain of carbon atoms on one end of the molecule. On the other end, they have either a Na or a K salt of a carboxylic acid-COOH group.

Soap The long nonpolar tail mixes with oils and dirt while the polar head attracts water molecules. This attraction helps wash away dirt and oil linked to the soap

What are commercial soaps & detergents? A long-chain fatty acid from natural oils like canola, palm and coconut is reacted with sodium or potassium hydroxide to make simple soaps. Sometimes tap water contains metal ions (Ca, Mg, & Fe) that react with soap replacing the Na or K ions making soap insoluble in water. Ions separate out of solution in the form of soap scum.

What are commercial soaps & detergents? Detergents are like soap except they are made with petroleum molecules instead of from natural fatty acids with a sulfonic group at the end instead of a carboxylic acid group. Detergents leave less soap scum, increase sudsing & improve cleaning in hard water. Can cause foam in water treatment plants & in streams.

Versatile Esters Esters are organic versions of salts, made from acids with water as a product of the reaction. Instead of reacting with bases, acids react with alcohols that have a hydroxyl group to produce esters. Esters are used to make soap, flavoring, perfumes & fibers for clothing.

How are esters used for flavors? Many drinks taste like real fruit but do not contain any fruit, only artificial flavors such as pineapple, banana, orange, apricot, & apple. The reaction to prepare esters involves removing a molecule of water from an acid & an alcohol.

What are polyesters? Synthetic fibers resulting from a reaction between an organic acid and alcohol produces long, nonpolar chains of many, or poly, esters. These fibers may be used alone or woven or knitted with natural fibers to make strong, water repellant, & colorfast fabric.