Text 6 cell phone chemistry

A typical cell phone contains some of the most valuable elements on Earth. With everything from gold to silver, it’s like having a little treasure chest in your pocket. A smart phone is packed with at least 40 elements.

BATTERY. When you turn on your phone, positively charged lithium ions move through a lithium-salt solution that conducts electricity. Electrons flow out of the battery, producing the electric current that powers your phone. The rechargeable battery’s casing is made of aluminum.

CIRCUITRY. The circuit board has gold, copper, and silver—good electrical conductors. The connectors (pins that join circuits to the circuit board) are coated in gold because it’s highly resistant to corrosion. The wiring is copper. Solder—an alloy of tin, silver, and copper—binds parts of the circuit board.

COMPUTER CHIP. The chip is the phone’s brain. It has many transistors made of antimony, phosphorus, and gallium arsenide (GaAs). Transistors act as paths and switches that tell the phone to follow or stop following commands. The chip is embedded with silicon—which has low conductivity—to channel electricity only through the conductive transistors.

TOUCH SCREEN. A thin layer of indium tin oxide—a mixture of indium oxide (In₂O₃) and tin oxide (SnO₂)—conducts electricity. When you touch the screen, a change in the electrical field occurs and communicates your finger’s location to the phone’s chip.

GLASS. Smartphone screens contain aluminosilicate glass, made from the compounds alumina (Al₂O₃) and silica (SiO₂). If you’ve ever dropped your phone and its screen has stayed intact, you can thank potassium ions (atoms that have gained or lost electrons). They help strengthen the glass.

DISPLAY. A cell phone’s display contains several rare earth elements. These elements are spread out widely in Earth’s crust, making them hard to mine. Small quantities of yttrium, europium, and dysprosium help produce the colors on the phone’s liquid crystal display (LCD) screen. Gadolinium, lanthanum, and terbium give the screen its glow.

MICROPHONE AND SPEAKERS. The microphone’s wafer-thin diaphragm, which vibrates when sound waves strike it, is made of nickel. The vibrations are converted into an electrical current that becomes the audio signal.

Magnets vibrate in the speaker to create audible sound. Magnets of neodymium (Nd₂Fe₁₄B) are used because they’re the strongest magnets, so even though they’re small, they’re powerful.

Text 7 alcohols

In chemistry, an alcohol is any organic compound in which the hydroxyl functional group (-OH) is bound to a saturated carbon atom. The term alcohol originally referred to the primary alcohol ethyl alcohol (ethanol), the predominant alcohol in alcoholic beverages.

Alcohols have an odor that is often described as “biting” and as “hanging” in the nasal passages. Ethanol has a slightly sweeter (or more fruit-like) odor than the other alcohols.

In general, the hydroxyl group makes the alcohol molecule polar. Those groups can form hydrogen bonds to one another and to other compounds (except in certain large molecules where the hydroxyl is protected by steric hindrance of adjacent groups). This hydrogen bonding means that alcohols can be used as protic solvents. Two opposing solubility trends in alcohols are: the tendency of the polar OH to promote solubility in water, and the tendency of the carbon chain to resist it. Thus, methanol, ethanol, and propanol are miscible in water because the hydroxyl group wins out over the short carbon chain. Butanol, with a four-carbon chain, is moderately soluble because of a balance between the two trends. Alcohols of five or more carbons (pentanol and higher) are effectively insoluble in water because of the hydrocarbon chain's dominance. All simple alcohols are miscible in organic solvents.

Because of hydrogen bonding, alcohols tend to have higher boiling points than comparable hydrocarbons and ethers. The boiling point of the alcohol ethanol is 78.29 °C, compared to 69 °C for the hydrocarbon hexane (a common constituent of gasoline), and 34.6 °C for diethyl ether.

Alcohols, like water, can show either acidic or basic properties at the -OH group. With a pK_a of around 16-19, they are, in general, slightly weaker acids than water, but they are still able to react with strong bases such as sodium hydride or reactive metals such as sodium. The salts that result are called alkoxides, with the general formula RO^- M⁺.

Meanwhile, the oxygen atom has lone pairs of nonbonded electrons that render it weakly basic in the presence of strong acids such as sulfuric acid. For example, with methanol.

Alcohols can also undergo oxidation to give aldehydes, ketones, or carboxylic acids, or they can be dehydrated to alkenes. They can react to form ester compounds, and they can (if activated first) undergo nucleophilic substitution reactions. The lone pairs of electrons on the oxygen of the hydroxyl group also makes alcohols nucleophiles. For more details, see the reactions of alcohols section below.

As one moves from primary to secondary to tertiary alcohols with the same backbone, the hydrogen bond strength, the boiling point, and the acidity typically decrease.

Hydroxyl groups (-OH), found in alcohols, are polar and therefore hydrophilic (water loving) but their carbon chain portion is non-polar which make them hydrophobic. The molecule increasingly becomes overall more nonpolar and therefore less soluble in the polar water as the carbon chain becomes longer. Methanol has the shortest carbon chain of all alcohols (one carbon atom) followed by ethanol (two carbon atoms.)

Alcohols have applications in industry and science as reagents or solvents. Because of its relatively low toxicity compared with other alcohols and ability to dissolve non-polar substances, ethanol can be used as a solvent in medical drugs, perfumes, and vegetable essences such as vanilla. In organic synthesis, alcohols serve as versatile intermediates.