AY Honors/Chemistry/Answer Key

1. Define the following terms:

a. Elements

A class of substances that cannot be separated into simpler substances by chemical means.

b. Compounds

A uniform substance composed of two or more elements.

c. Chemical symbols

Every element is represented using an abbreviation of one or two characters that represent the name of the element. The first character is always capitalized, and the second character if it exists is always lower case.

H represents hydrogen

He represents helium

Li represents lithium

Some of the symbols do not represent the modern name, but an original name.

Ag represents argentium (Latin) or silver

Au represents aruium (Latin) or gold

W represents wolfrom (German) or tungsten

There are 92 elements that are found naturally on earth, and there are another 26 that have been created in atomic accelerators, and have very short half lives. All of these elements are organized using a "Periodic Table of Elements" which was created by Dimitri Mendeleev.

d. Solutions

A mixture of two or more substances that do not react chemically. If you dissolve sugar salt or another substance in water, you are creating a solution.

e. Atoms

Atoms are basic building blocks of matter. Atoms range in size from .5Å to 24Å. ( Å is the symbol for a unit of measure known as an angstrom. A blond hair is between 170,000 and 500,000Å in diameter and a black hair is between 560,000 and 1,810,000Å in diameter)

We cannot directly see atoms with a regular microscope. The positions of the electron cloud around and atom can be determined using X-ray crystalography, or scanning tunneling microscope. The center of an Atom is "viewed" by using a neutron beam. Light has a wavelength of between 4,000Å and 7,000Å which is like 1000 times the diameter of an atom. Because the wavelength of light is so long it has almost no interaction with the atom.

Hydrogen is the simplest atom, it is made of one proton and one electron. A classical model of an atom is to think about the electron orbiting the central proton. If we created a model of this atom with the proton the size of a basket ball, then the electron would be the size of a grain of salt and will be orbiting at a distance of 40,000 feet.

Atoms are mostly empty space, but because the electrons are moving so rapidly, the matter we touch can feel very solid.

f. Molecules

Two or more atoms that have bonded to each other using the electromagnetic force.

g. Periodic Table

The periodic table of the chemical elements is a tabular method of displaying the chemical elements. The table illustrates recurring ("periodic") trends in the properties of the elements.

h. Combustion

We often use the word burn to describe the chemical process of a fuel combining rapidly with a oxidizer (usually oxygen). This process usually is associated with flames, light, heat, and smoke.

i. Acid

The word acid is from the Latin word acidus which means sour. In the early days of chemistry, it was a common practice to taste or smell things and record the sensation. Many things that are acidic are sour. Lemon juice is sour because of the citric acid in it.

Because many substances can be toxic, this probably killed a number of chemists including the famous scientist, Humphry Davy, the man who came up with the theory that explained the nature of an acid.

Davy's hypothesis was that acids were substances that contained replaceable hydrogen. This hydrogen could be replaced by metals and this reaction would leave behind a salt.

2HCl + Zn → ZnCl₂ + H₂

Fe + H₂SO₄ → H₂ + FeSO₄

j. Salt

A salt is a term for the solid form of an ionic compound, such as Sodium Chloride (Na⁺Cl^-) or potassium hydroxide (K⁺(OH)^-).

k. Proton

A positively charged particle that is a part of the nucleus of an atom. Protons have a mass of [math]\displaystyle{ 1.67 \times 10^{-27} }[/math] kg. One cubic centimeter of water contains [math]\displaystyle{ 6.02 \times 10^{24} }[/math]protons that form the nucleus of the atoms of hydrogen and oxygen. Hydrogen has one proton at its center and oxygen has 8 protons.

l. Neutron

A neutrally charged particle that is a part of the nucleus of an atom. Neutron's have a mass of [math]\displaystyle{ 1.67 \times 10^{-27} }[/math] kg. When we look at water we find that it is made up of Hydrogen and Oxygen. Hydrogen has no neutrons, but each atom of oxygen has 8 neutrons.

Neutrons are held together by what is called the "Weak Force". Free neutrons decay with a half life of about 10.3 minutes into a proton, electron and an electron nutrino. In the neucleus of an atom, the neutrons can be quite stable because of another force known as the "Strong Force"

m. Electron

A negatively charged particle with a mass of [math]\displaystyle{ 9.11 \times 10^{-31} }[/math] kg. Electrons form a cloud about the positively charged nucleus of an atom.

n. Distillation

Distillation is a technique of separating chemical substances (usually liquids) based on the temperature at which they evaporate. The farther apart the boiling temperatures, the more likely that the distillation will be successful. Success also depends on the interactions between particles, since two dissimilar liquids that are dissolved in each other are likely to form azeotropes. If this occurs, the liquid and gas phase will both have the same composition and therefore boiling will not cause further separation.

o. Fractional Distillation

Fractional distillation is a technique in which several distillations occur in the same column, mediated by some sort of porous medium. It allows the separation of substances with closer boiling points than simple distillation, and also makes the distillation of the same solutions more efficient.

p. Filtration

Filtration is a technique in which a solid precipitate is separated from a liquid. The mixture is placed on filter paper, which allows the liquid to pass through, leaving the solid behind. Typically the liquid is first brought to a temperature such that there is little solid dissolved in the liquid, so that separation is most effective.

2. What gases extinguish life, and how? Explain the principle of one kind of chemical fire extinguisher.

In the extreme, almost any gas can kill a person. Even pure oxygen can kill because the body cannot deal effectively with pure oxygen. The gases can kill by:

1) Suffocation- The gas displaces oxygen and the body now starved of oxygen dies. Some of the most dangerous suffocants are oxidation compounds such as [math]\displaystyle{ CO_2 }[/math] or CO

2) Poison- There are gases such as Cyanide gas HCN which are highly poisonous. Cyanide binds to the iron atoms in the enzyme known as cytochrome c oxidase and thus blocks the production of ATP. ATP is the universal energy currency of all living organisms.

3) Explosion- Many gases are quite flammable and can explode quite destructively. Most of the light Hydrocarbons in mines can be set off with only a small spark.

Fire, like life, requires oxygen, so a common method used in fire extinguishers is to use a gas or liquid that will keep the oxygen from getting to the fuel.

3. Name two common sources of carbon monoxide. Why is it dangerous?

Automobile exhaust before the catalytic converter contains large amounts of CO (Carbon Monoxide). If the exhaust system is damaged before this point, then there is a danger of breathing the suffocating gas. Because CO is odorless, a damaged exhaust system could be fatal.

The catalytic converter converts most of the CO to [math]\displaystyle{ CO_2 }[/math] (Carbon Dioxide) There may still be enough CO in automobile exhaust to be fatal, but since most is now [math]\displaystyle{ CO_2 }[/math] which has an odor or at least sensation, there is less chance of accidental asphyxiation. [math]\displaystyle{ CO_2 }[/math] can be fatal as well, but is quite caustic, creating a burning sensation in the nose and lungs. If you have ever breathed the bubbles from a Soda Pop can, you have smelled [math]\displaystyle{ CO_2 }[/math].

Another common source of CO is natural gas or propane stoves, heaters, hot water heaters, or clothes dryers. If these appliances become damaged they can be quite dangerous. It is a good idea to have a CO detector near an old furnace or water heater to provide an early warning.

4. What are the states of matter?

The states of matter are largely defined based on the level of interaction between the molecules and atoms that form the matter. This interaction is temperature dependent, and there are well defined freezing points, melting points, boiling points, condensation points, and ionization energies for each element or molecule.

Solid

The atoms are in a fairly rigid structure that at the macroscopic level feels hard or solid. The atoms may be arranged in a very rigid crystaline structure, but there is still vibration within the structure.

Liquid

The atoms are free to move around, but do not separate like a gas. Liquids can flow and in general do not feel solid or rigid. Liquids are not compressible.

Gas

The molecules of a gas are completely free to move around and at standard room temperature they move tens of meters before hitting another molecule. A gas is airy. You will not necessarily know that it is there unless you move through it and feel the wind.

Plasma

The molecules of a plasma are ionized, which causes them to repel each other, so a plasma can appear to flow almost like a liquid, and it glows as some of the molecules change ionization states.

Liquid Helium

When liquid helium is put close to absloute zero, it behaves oddly. It turns into a superfluid. It is dangerous to handle because of its temperature.

In many ways, the modern idea of solid, liquid, gas, and plasma is equivalent to the old alchemy idea of the four elements earth, water, air, and fire.

5. Do five of the following, and explain the chemical action that takes place:

a. Try to light a sugar cube, first without and then with some ash applied to the cube, thus showing the action of a catalyst.

Materials

• Sugar Cubes
• Ash from fireplace or campfire
• Matches or lighter
• Aluminum foil
• Piece of wood or trivet to act as insulator

Method

• Lay a piece of aluminum over the trivet or a piece of wood.
• Place the sugar cube near the center of the foil.
• Take another sugar cube and coat it with ash.
• Place the ash-coated sugar cube next to the first sugar cube, but do not let them touch.
• Try to light each sugar cube. It should be easier to light the ash-coated sugar cube.

b. Place an ice cube in a glass of water, place a four-inch (10.2 cm) string on top of the glass and ice, then solve the problem of taking the ice cube out of the water without touching it.

Materials

• Ice
• Salt
• Water
• Glass
• String 10 cm long

Method

• Put the ice cube in the glass
• Tie a loop on the string and place it on the cube
• Put a pinch of salt on the loop and cube
• Wait a while then pull up the string

c. With the use of water, turpentine, and soap, transfer a newspaper picture to a blank sheet of paper.

Materials

• 30 ml soap powder (example: Ivory Snow)
• 60 ml hot water
• 15 ml turpentine
• Small bowl
• Measuring cup
• Paint brush
• Newspaper or old magazine

Method

• Dissolve soap powder in hot water and then add turpentine.
• To use, dip a brush into the ink and brush over the picture to be transferred, wait about ten seconds then place a piece of paper over the picture and rub the back of it with a spoon. The picture will be transferred to the paper.

The ink will solidify in its container after a little while. To reverse this simply set the bottle in a pan of warm water until melted and then shake.

f. Place a fresh egg in fresh water and then salt water, noting the difference.

Materials

• Fresh (uncooked) egg
• 1 liter Water
• 120 ml Salt
• 2 Bowls

Methods

• Add the salt and a half liter of water to a bowl and stir until the salt dissolves.
• Add the other half liter of water to the other bowl - do not add any salt.
• Place the egg in the salted water. It should float
• Move the egg to the unsalted water. It should sink.

Salt water is more dense than fresh water, meaning that a volume of salt water will weigh more than an equal volume of fresh water. The density of an egg is between the density of salt water and fresh water. An item will float if it is less dense than the liquid in which it is placed. Since the egg is more dense than fresh water, it sinks. But because the egg is less dense than the salt water, it floats.

g. Demonstrate that rust uses up oxygen with the use of steel wool, a pencil, a rubber band, a water glass, and a dish of water.

Materials

• Steel wool
• Pencil
• Rubber band
• Drinking glass (clear glass)
• Bowl
• Water

Method

Use the rubber band to attach the steel wool to the eraser end of the pencil

i. Make an invisible ink.

Materials

• Water
• Vinegar, Lemon juice, sugar, onion
• Small cups
• Candle or stove flame
• Tooth picks
• Paper

Methods

You can mix vinegar, lemon juice, sugar or onion juice with water to create an invisible ink. To make the ink visible, carefully hold it over a heat source. The "ink" will turn colors and become visible. Try mixing a small amount of ink using each type of ingredients to see which works better.