Nivaldo J. Tro Mark Erickson Hartwick College Chapter 15 The Chemistry of Household Products

Cleaning Clothes We take advantage of the properties of certain molecules to remove undesirable molecules from surfaces. We will try to understand the properties of these various products in terms of the molecules that compose them.

Soap Polar molecules have an uneven electron distribution. Nonpolar molecules have an even electron distribution. –Polar and nonpolar molecules do not interact. Soap molecules are relatively lengthy and have both an ionic (polar) end and a nonpolar end.

Concept Check 15.1 Sodium stearate is a molecule commonly used as a soap. Identify the polar and nonpolar components of sodium stearate from the structure provided.

Concept Check 15.1 Solution Sodium stearate has both polar and nonpolar components in its structure. The nonpolar tail is hydrophobic and the ionic polar head of the molecule is hydrophilic.

Surfactants Surfactants are so named because they act at surfaces. These colloidal suspensions are a type of emulsion and soap functions in them as an emulsifier or emulsifying agent. The particles in a colloidal suspension are too small to see with the naked eye, but they make a solution cloudy because they scatter light.

Micelles Nonpolar tails crowd into a spherical ball. –Hydrophobic tails maximize interaction with each other. –Hydrophilic heads maximize interaction with the water which, like them, is polar. Soap molecules congregate at the surface of a liquid. Once the surface becomes crowded with soap molecules, additional soap molecules will cluster in structures called micelles.

Micelles Micelles in “dirty” water contain clumps of greasy (nonpolar) material. This mixture of one substance dispersed in a finely divided state throughout another is called a colloidal suspension.

Synthetic Detergents Mg +2 and Ca +2 ions in hard water form curd with soap, reducing its effectiveness. Curd coats otherwise clean surfaces. In the 1950s chemists solved this problem with synthetic alkylbenzenesulfonate (ABS) detergents. 2CH 3 (CH 2 ) 16 COO - + Ca 2+  (CH 3 (CH 2 ) 16 COO - ) 2 Ca 2+ Soap Hard Water Ions Curd

ABS Detergents Due to their highly branched alkyl chains, ABS detergents do not biodegrade. Soapy coastlines and inland bodies of water made a modification of ABS detergents necessary.

LAS Detergents Subsequent detergent designs had alkyl chains more like the linear alkyl chains found in soap. They did biodegrade into CO 2, H 2 O, and SO 4 2-, all common substances in the environment.

Types of Detergents Anionic-alkyl chain has a negatively charged group –ABS, LAS Cationic-alkyl chain has a positively charged group Nonionic-alkyl chain maintains polarity with OH or similar groups A cationic detergent

Concept Check 15.2 What structural features do soaps and detergents have in common?

Concept Check 15.2 Solution Both soaps and detergents have a long nonpolar hydrocarbon tail and an ionic (polar) head.

Laundry Cleaning Formulations Surfactants –Recent trends favor a combination of anionic LAS with nonionic detergents. Builders –Primary function is to soften water –Also help to suspend solid particles in solution once removed from fabric –The best is sodium tripolyphosphate But it leads to eutrophication of lakes –Sodium carbonate and zeolites are replacements.

Laundry Cleaning Formulations Fillers –Control consistency and density of packaged product –Have no effect on cleaning Enzymes/Bleaching agents –Help degrade stains by a different mechanism Brighteners –Dye molecules that make clothes appear brighter –They absorb UV and emit visible light in the blue

Corrosive Cleaners Drain cleaners –Sodium hydroxide (NaOH) dissolves in water in an exothermic reaction, melting grease in clogs and dissolving protein strands in hair. –Al in NaOH produces bubbles of H 2 gas to physically dislodge clogs. Toilet bowl cleaners –Many are acidic solutions of hydrochloric acid or citric acid that dissolve calcium carbonate deposits left by hard water.

Hair Products: Curling Hair Hair is mainly keratin (long coiled amino acid chains-protein) and can be curled or uncurled by changes in: –Presence of moisture Affects hydrogen bonds –pH Salt bridges between keratin proteins are strongest under slightly acidic conditions. –Chemical exposure Make and break disulfide linkages

Washing and Conditioning Hair Shampoos’ primary purpose is the removal of dirty sebum (a mixture of wax, fat, and dead fat-producing cells) from the scalp. –Synthetic detergents help eliminate hard water residue. Conditioners are cationic surfactants that help remove residual shampoo and coat hair, making it more manageable.

Coloring Hair Natural color –Melanin: Dark pigment –Phaeomelanin: A red-orange pigment Lightening of hair color requires removal of these pigments by using bleach. Darkening of hair color means applying a dye to the hair surface –Temporary: Large dye molecules attach only to the surface of the hair strands. –Permanent: Smaller dye molecules defuse into hair strands and react to produce larger colored molecules.

Skin Products Used to manage the sebum-lubricated dead cells and underlying live cells as well as the moisture content of skin Too dry, flaking; too moist, risk of infection Optimal moisture content is 10%.

Creams and Lotions Both contain water to add moisture to skin and oil to hold the moisture to the skin. Lotions contain more water than oils. –Olive, mineral, and almond oils, lanolin Creams contain more oils than water. –Waxes such as beeswax and carnauba Emulsifying agents keep the oil and water in an emulsion.

Sunscreens Lotions with UV light-absorbing ingredients Skin produces melanin, which protects against further UV light exposure. Sun also damages fragile biological molecules, producing sunburn. A thin layer of these compounds applied to the top of skin prevents UV-B (which appears to be the most harmful of UV radiation) from reaching skin. Exposure to UV light can result in skin cancer, premature aging, and a weakened immune system.

Concept Check 15.3 Which UV light has more energy, UV-A or UV-B?

Concept Check 15.3 According to Figure 15-13, UV-A light has wavelengths between 320 to 400 nm and UV-B has wavelengths between 280 to 320 nm. Chapter 7 taught us that the energy of light is inversely proportional to the wavelength of light. UV-B light has the shorter wavelength, therefore, it has higher energy and more harmful to humans.

Facial Cosmetics Most contain waxes, oils, pigments, dyes, and perfumes. Lipstick –Pigment (usually titanium dioxide) gives brightness and cover. –Dye (a bromoacid) provides color. –Oils and waxes are the base for the pigment and dye and help keep lips soft and moist.

Cosmetics Foundation –These are oil and water emulsions with a soap- like emulsifying agent. –Face powders contain talc, calcium carbonate, pigments and dyes. –Other moisture- absorbing substances and dyes Mascara –Soap, oils, waxes, and pigments –Possible pigments include iron oxide (brown) and carbon black (black)

Perfumes and Deodorants: Producing Pleasant Odors and Eliminating Unpleasant Ones There are about 50 million chemical receptors in the human nose. Some molecules fit receptors and trigger the brain to interpret an odor as pleasant or unpleasant, depending on the receptor triggered. Odorless molecules simply don’t fit the receptors. Brain processing centers for smell are linked with those that process emotion.

Making Perfume Chemists now synthesize the chemicals that were once derived from plant and animal sources. Perfumes are designed to be experienced in three stages. –Top note: Refreshing, first out of the bottle –Middle note: Larger molecules, persist on skin –End note: More animal and earthy fragrances, least easily evaporated Fragrance concentration –Perfume is 10–25% in alcohol –Cologne is 0.5-2% in alcohol

Concept Check 15.4 Which molecule, myrcene or vanillin, is more likely to be the end note of a perfume?

Concept Check 15.4 Solution Myrcene is a hydrocarbon with no polar bonds. With very weak intermolecular forces, myrcene would be expected to evaporate quickly (the top note). Vanillin is a polar molecule with very polar O-H bonds along with polar C—O and C=O bonds. Polar molecules like vanillin are less volatile and thus evaporate more slowly (the end note).

Deodorants and Antiperspirants Deodorants either mask or reduce body odor. –Bacteria that live in warm moist body areas actually produce smelly compounds from organic compounds in sweat. –Antibacterial agents kill this bacteria. Antiperspirants reduce the amount of perspiration that escapes from sweat glands. –Aluminum chlorohydrate, Al 2 (OH) 4 Cl 2, constricts the opening of sweat glands. Triclosan, an antibacterial agent

Polymers and Plastics Polymers are long chain structures composed of individual repeating units. –Individual units are called monomers Properties of polymers may include high strength, low cost, variable properties, and the ability to be molded into any shape. The simplest and most common polymer is polyethylene, which is derived form the ethylene monomer.

Polymers and Plastics Ethylene units link to each other by having their double bonds broken. Single bonds form between these units. The repeating CH 2 units can number in the thousands.

Microscopic/Macroscopic Polyethylene chains resemble waxes but are longer resulting in greater hardness and higher melting points. Two types: –LDPE (branched) –HDPE (unbranched) Polymer chains have different branching and properties. Because the structure of polyethylene resembles the structure of long-chain hydrocarbon waxes, its properties are similar to wax. Both wax and polyethylene repel water.

Concept Check 15.5 What are the differences between LDPE and HDPE?

Concept Check 15.5 Solution LDPE (low density polyethylene) is a polyethylene polymer that has high degree of branching along the polymer chain. LDPE is a soft and flexible plastic used in garbage bags and shopping bags. HDPE is formed under conditions that allow the growth of long chains, with little to no branching. The chains pack efficiently resulting in a denser and tougher plastic which is used in beverage, bleach, and antifreeze containers.

Polymer Terminology Thermoplastic –Material softens when heated –Hardens when cooled –Can be heated and remolded many times Addition polymer –Formed by the simple addition of monomer units –No atoms or small molecules are eliminated during polymerization.

Polymer Terminology Many other polymers can be thought of as substituted polyethylenes. Polypropylene Polyvinyl chloride Polystyrene

Polymer Related to Polyethylene

Concept Check 15.6 Give the structure for the monomer used to form the addition polymer, polyvinyl acetate.

Concept Check 15.6 Solution The monomer is the simplest repeating unit with a double bond in place of the single bond, which in this case is vinyl acetate.

Polyethylene Terephthalate (PET) PET is a polyester (repeating ester groups, —RCOOR—). –A condensation polymer Dacron –Drawn into fibers –Cloth Mylar –Thin sheets –Packaging –Sails –Videotapes Polymers that expel atoms, usually water, during their formation are called condensation polymers.

Polycarbonate: Lexan Lexan is a polycarbonate and a condensation polymer. Clear tough plastic material Tough enough to act as bullet-proof windows Eye protection and scratch-proof coatings on eyewear

Concept Check 15.7 Why are polymers like Lexan, PET, and nylon considered condensation polymers? Why are they also considered copolymers?

Concept Check 15.7 Lexan, PET, and nylon are considered condensation polymers because during their formation, small molecules such as water are expelled for each bond that forms linking monomer units. They are also considered copolymers because they are composed of alternating single repeating units.

Concept Check 15.8 Give the condensation copolymer made and small molecule released by reacting the following two monomers together:

Concept Check 15.8 Solution Kevlar ® is made from the following diamine and dicarboxylic acid. Water is the small molecule released during the reaction.

Rubber Elastomer: Stretches easily and returns to its original shape A natural product that is now made synthetically in a number of forms. Used in bicycle and motor vehicle tires, building foundations, and bridge bearings

Vulcanization Polyisoprene loses its original conformation at increasing temperatures. Vulcanization makes it harder and more elastic. Charles Goodyear, 1839 In this process, sulfur atoms form cross-links between the polyisoprene chains. These cross- links still allow the polymer chains to uncoil under stress, but the cross-links force the chains to snap back to their original positions when the stress is released, even if the rubber is warm.

Copolymers Composed of more than one type of monomer Resulting chains have alternating units rather than a single repeat unit. When copolymers form, a small molecule (usually water) is expelled. Condensation polymers –Polymerizations that expel water –Nylon  Adipic Acid and Hexamethylenediamine

Copolymers: SBR A copolymer of styrene (25%) and butadiene (75%) Used extensively to replace natural rubber in automobile tires Ages better than natural rubber Formed via addition polymerization

Chapter Summary Molecular Concept Surfactants Synthetic detergents Hard water Polymers Rubber Societal Impact Our lives would be very different and dirty without surfactants. Plastics have had an impact on society by providing cheap, durable materials from which to build everything from sandwich wrappers to cars.