chemistry and society final - chapter 8

hydrogen peroxide

- H2O2 - as a dilute aqueous solution, peroxide is used to bleach hair, clean wounds and ulcers

potassium dichromate

- K2Cr2O7 - orange substance that turns green when it is reduced - early breathalyzers used this because it is reduced by alcohol (then added catalysts to speed up the reaction > silver nitrate)

electrochemical cell

- a device that produces electricity by means of a chemical reaction - in the electrochemical cell pictured, there are two separate compartments, one contains cooper metal in a blue solution of cooper(II) sulfate and the other contains silver metal in a colorless solution of silver nitrate. copper atoms give up electrons more easily than silver atoms do, so electrons flow away from the copper compartment towards the silver. the copper metal slowly dissolves as copper atoms give up electrons to form copper(II) ions. the electrons flow through the wire to the silver compartment were silver ions pick them up to become silver atoms. - the two pieces of metal where electrons are transferred are called electrodes. the electrode where oxidation oxidation occurs is called anode. the one where the reduction occurs is called cathode

fuel cells

- a device that produces electricity directly from continuously supplied fuel and oxygen - The fuel is oxidized at the anode and O2 is reduced at the cathode. The electrons are allowed to flow through a wire and do work - does not got dead as long as the reactants are supplied - these are more efficient than just burning fossil fuels

oxygen occurrences

- as O2 molecules in the atmosphere (21%) - combined by H in the hydrosphere - combined with silicon (sand is SiO2), aluminium, and other elements - pure oxygen is obtained by liquefying air and then letting the nitrogen and argon boil off

disinfectants and antiseptics

- both are used to destroy microorganisms - antiseptics are applied to living tissues - disinfectants to non-living things. a good example is chlorine which is used to kill disease-causing microorganisms in drinking water >hypochlorous acid is the disinfecting agent (created by water and chlorine) > but although chlorine kills harmful organisms, it can also oxidize small molecules and for harmful products like chloroform

2-V cells

- both electrodes are different, one is made out of lead and the other si made out of lead dioxide (they are surrounded by sulfuric acid) - they can be recharged - lead is toxic and sulfuric acid is corrosive

Hydrogen Fuel Cell Cars

- car powered entirely by a hydrogen fuel battery - it has a hydrogen storage tank, which provides the fuel for the vehicle - hydrogen is taken from the tank to the fuel cell stack - electricity is generated there though a chemical reaction between hydrogen and oxygen from the air - then it moves into the power control module and there the electricity is conditioned so that it can be used by the electric vehicle - this causes a huge reduction the greenhouse gases, carbon dioxide is reduced by 30-40%, and its only byproduct is water - drawbacks: very expensive and hydrogen does not exist naturally by itself and the most natural way of producing it is though natural gas

ore to seek (video)

- coke: result of burning the impurities and junk out of coal. burns cleanly and that's what you need - in the plant, the super heated air burns the coke and blasts away the oxygen and that's when you get pure iron - the carbon in the coke bonds with the iron - the mixture liquifies under the extreme heat - impurities rise to the top and the heavier iron sinks to the bottom - pig iron is the iron that has over 4% (more brittle) - to become steel that number needs to be reduced to less than 2%

battery

- collection of electrochemical cells

corrosion vs. explosion

- corrosive reactions are often quite slow - a chemical explosion is usually an extremely rapid redox reaction often accompanied by a considerable increase in volume - the redox reaction often involves a compound of nitrogen

oxidizing agent

- element or compound which causes the oxidation - substance being reduced

reducing agent

- element or compound which causes the reduction - substance being oxidized

hydrogen

- excellent reducing agent - can free metals from their ores but it is generally used to produce more expensive metals like tungsten - by mass, it makes up only about .9% of the Earth's crust but it ranks third in abundance by number of atoms - used for the preparation of ammonia and methanol, also to hydrogenate vegetable oils

celular respiration

- food metabolization process that gives us energy - it converts everything we eat into carbon dioxide, water, and energy

free radicals (video)

- free radicals are molecules with broken bonds thus they are highly reactive - these are generated in the body as a result of the body generating energy (mitochondria > controls oxidation process of food) - mitochondria reduces the oxygen into water, but in order to do so, it first converts the oxygen into a radical called superoxide (which doesn't get further reduced) - this can cause damage to proteins or DNA - antioxidants neutralize the effect of free radicals (vitamin c, e) - oxidative stress: too many free radials produced (unfit person does running) - the production of free radicals when we exercised sends a message to the entire body to chin them up so that they are able to function better next time we exercise

electrolysis

- in electrolysis, electricity supplied externally causes a chemical reaction to occur - this is what is often used to reverse reactions and recharge something

ANFO (Ammonium Nitrate mixed with Fuel Oil)

- inexpensive and effective explosive, widely used for mining salt, coal, and other minerals - when ANFO explodes, ammonium ion is the reducing agent and nitrate ion is the oxidizing agent - the fuel provides additional oxidizable material - starting materials are both liquid and solid, and they produce gaseous products

preparation of metals

- metals are often found in compounds - to prepare the free metals, compounds must be reduced - coal and coke is used to reduced this compounds - they can also be reduced by heating its ore with a more active metal (aluminium)

other batteries

- most are made out of lithium > provide much energy and have a compact volume - another competitor is NiCad cell (Cd anode, NiO cathode) often used in portable radios and cordless appliances - nickel-metal hydride cell

rusting of iron

- oxidation and reduction often occurs at different ends of the metal's surface - electrons are transferred through the iron metal > the circuit is completed by an electrolyte in aqueous solution - the metal is pitted at an anodic area, were iron is oxidized - these ions migrate to the cathodic area, were they react with hydroxide ions formed by the reduction of oxygen - the anodic area is protected from oxygen by a water film while the cathodic area is exposed to air

oxidation (oxidized)

- oxidation: when oxygen combines with other elements or compounds - oxidized: when substances combine with oxygen they are said to be oxidized - concept expanded to include chloride, bromine, or other non-metals

bleach

- oxidizing agent - removes unwanted color from fabrics or other materials - most of them work by oxidizing carbon-carbon double bonds in the colored substances to single bonds - these are typically sodium hypochlorite (NaOCl) > aqueous solution known as bleaching powder - non-chlroine bleaches (oxygen bleaches) contain sodium percarbonate or sodium perborate (combinations with hydrogen peroxide

photochromic glass

- photochromic lenses darken when exposed to light - this can be explained by reduction-oxidation reactions - photochromic lenses have silver have silver chloride (AgCl) and copper(I) chloride embedded in the glass - silver chloride is susceptible to oxidation and reduction by light (1) the light displaces an electron from a chloride ion (2) the electron then reduces a silver ion to a silver atom - clusters of silver atoms block the transmittance of light causing the lenses to darken and the degree of darkening depends on the intensity of light - the copper(I) chloride reverses the process - when the lenses are removed from the light, the chlorine atoms formed by the exposure to light are reduced by the copper(I) ions, which are oxidized to copper(II) ions - the cooper(II) ions then oxidize the silver atoms - the net effect is that the silver and chlorine atoms are converted to their original oxidized and reduced states and the lenses become transparent once more

formation of silver crystals (video)

- pour colorless silver nitrate solution into a recipient with copper coil - as it touches the coil, the copper immediately darkens and thickens - copper is reducing silver ions to silver - the solution turns blue because copper ions are formed

reduction

- reduction: opposite of oxidation - when hydrogen burns, it combines with oxygen to form water: * hydrogen is oxidized in this reaction * at the same time, oxygen is reduced - oxidation and reduction always happen at the same time and in exactly equivalent amounts

catalyst

- substance that increases the rate of a chemical reaction without itself being used up - catalysts lower the activation energy (minimum energy needed to get a reaction started) - examples of catalysts: nickel, palladium (can absorb up to 900 of its own volume of hydrogen), and platinum - good thing for green chemistry is that it provides a pathway for reactants to combine in a more effective manner

dry cells

- the anode reaction is the oxidation of the zinc cylinder to zinc ions - the cathode reaction is the reduction of manganese dioxide - the ordinary dry cell has largely been replaced by the alkaline cell, which is familiar but contains potassium hydroxide instead of ammonium chloride (these ones are more expensive but they last longer > in storage and in use)

silver tarnish

- the tarnish over silver results from oxidation of the silver surface by hydrogen sulfide in the air or from food - you can use silver polish to remove the tarnish but in doing so you also lose some part of the silver - an alternative involves the use of aluminium: requires an electrolyte and sodium bicarbonate - the silver ions are reduced to silver metal at the expense of the cheaper metal

ozone

- triatomic oxygen (O3) - powerful oxidizing agent and a harmful air pollutant - on the other hand, a layer of ozone in the upper stratosphere serves as a shield that protects life of Earth from ultraviolet radiation from the sun

iodine

- used as an antiseptic, either in an alcoholic solution (tincture of iodine) or in Lugol's iodine solution (no alcohol)

benzoyl peroxide

- used to treat acne

oxidation and reduction (3 ways to see it)

1) oxidation is a gain of oxygen atoms reduction is a loss of oxygen atoms 2) oxidation is a loss of hydrogen atoms reduction is a gain of oxygen atoms 3) oxidation is a loss of electrons (increase in oxidation number) > oxidation number increases as electrons are lost reduction is a gain of electrons (decrease in oxidation number)

reduction in photography

Black and white photographic paper contains a coating of silver bromide (AgBr). The silver ions that are exposed to light react with the developer (hydroquinone, C6H4(OH)2) to form metallic silver. The silver ions not exposed are removed using a solution of sodium thiosulfate. This produces a negative where the metallic silver is deposited.

reaction between zinc and sulfuric acid

Concentrated sulfuric acid reacts vigorously with zinc. The gas evolved is hydrogen from this highly exothermic reaction. this result can also be achieved with

cathode

a negative electrode at which reduction occurs (reducing agent) (were reduction occurs)

anode

a positive electrode at which oxidation occurs (oxidizing agent) (were oxidation occurs)

how are some batteries rechargeable?

a rechargeable battery uses a reversible redox reaction > the normal reaction provides electrical energy, applying electrical energy in the opposite direction using a charger reverses the reaction but not all can be reversed

alkali metals oxidation (video)

as you go down the group in the periodic table, the elements oxidize faster

electrode

carbon rod or metal stip inserted into an electrochemical cell, at which oxidation or reduction occurs

antioxidants

food chemistry's reducing agents (vitamin c, vitamin e, beta-catothene)

porous partition

ions flow through a porous partition from one half-cell to another

oxidants

oxidizing agents

aerobic exercise

physical activity under conditions in which plenty of oxygen is available

anaerobic exercise

physical activity under conditions where oxygen available is insufficient

photosynthesis

process by which plants synthesize carbohydrates (exactly the reverse of celular respiration)

protection of aluminum

the aluminium at the surface reacts with oxygen in the air to form a thin layer of oxide. but instead of being porous and flaky like iron oxide, aluminium is hard and tough and adheres strongly to the surface, protecting it from further oxidation - but salt can intervene and make it rust like iron