Before you even start taking a chemistry class, you should learn unit conversion and stoichiometry. It is very boring but once you understand how to do it the rest of chemistry will be a lot of fun.
Stoichiometry
Here are some examples of stoichiometry.
You are given 400g of NaCl and 1L of deionized water. What will be the concentration of the NaCl solution if you dissolve the NaCl in the water?
How many liters of H2 gas will it take to make 1 mol of H2O at Standard Temperature and Pressure?
How many moles of NaOH does it take to neutralize 350 mL of a 5M H2SO4 solution?
Unit Conversion
What is the molarity of a solution that contains 2oomg of Ca(OH)2?
What is the molality of that solution?
How many liters of water would it take to make a 1M solution with 5g of KOH?
Notice that all of this is algebra. There is no geometry or calculus or statistics. A large part of general chemistry can be thought of as math word problems.
Sunday, February 18, 2007
General Study Skills
When you answer a question on a test, you should ask yourself, “Is this answer articulate, and is it complete?” In other words, you want to make sure that your answer is clear and easy to understand and that it shows the teacher everything that you know about the subject.
If a test asks the question, what is an acid?
Most C students would say.
Something that breaks apart in water and one of those parts is H+.
Most B students would say.
Acids are substances with a low pH. There are many different ways to define an acid.
The Arrhenius definition of an acid is that an acid is a molecule that will break apart in water and give H+ to the solution.
Most A students would say.
Acids are substances with a low pH. That means it will have a pH well below 7.
The Bronsted definition of an acid is that it will donate a proton, H+, to other chemicals. The Arrhenius definition of an acid is that an acid is a molecule that will break apart in water and give H+ to the solution. Some strong acids are HCl, HNO3, and H2SO4. Acetic acid is a weak acid. This is what it looks like when it dissociates.
CH3COOH -> CH3COO- + H+
Core Concepts
These are some important concepts that we will cover. Most of them are very hard. My philosophy is that if you learn the hard stuff now, your classes will be super easy for you later on.
- How to write good answers to test questions and how to write good reports.
- Stoichiometry. Balancing chemical reactions and unit conversion.
- What a chemical reaction is, and what is not a chemical reaction.
- Basic kinetics. Rate laws, rate constants, catalysts, and energy barriers.
- The ideal gas law. Relationships between pressure, volume, and temperature.
- Lewis Structures and the shapes of molecules. Bonds and orbital hybridization.
- Significant figures
- How to name organic molecules and some very basic organic chemistry.
- The basic concepts of biochemistry and molecular biology.
Common Chemical Reactions
Everyone should know these classic patterns for inorganic chemical reactions.
Acid + Base = Salt + Water
Acid + Metal = Salt + Hydrogen Gas
Base + Metal = Salt + Hydrogen Gas
Salt + Salt = one new salt + two dissolved ions
This is called a methathesis or double replacement reaction.
If two girls trade boyfriends, that is a double replacement reaction.
Salt + Salt = two new salts
There are also classic organic reactions that are covered in another study guide.
Acid + Base = Salt + Water
Acid + Metal = Salt + Hydrogen Gas
Base + Metal = Salt + Hydrogen Gas
Salt + Salt = one new salt + two dissolved ions
This is called a methathesis or double replacement reaction.
If two girls trade boyfriends, that is a double replacement reaction.
Salt + Salt = two new salts
There are also classic organic reactions that are covered in another study guide.
Super Important Concepts
Intermolecular Forces
Intermolecular forces are not chemical bonds. They are weaker than chemical bonds. They determine the melting point, boiling point, and solubility of chemical compounds.
Molecules with lots of strong intermolecular forces, like hydrogen bonds, will have a high boiling point and a high freezing point. Compounds that have weak intermolecular forces will often be gasses at room temperature, or liquids with low boiling points.
Table I – The four types of intermolecular forces.
| Intermolecular Force | Strength | Example | Requirements |
| Hydrogen Bond | Strongest | Water | H attached to N, O, or F |
| π-cation | Strongest | Cobalt and Acetylene | Transition metal and double or triple bond. |
| dipole-dipole | Medium | Water, CHCl3 | Must be polar. |
| Van Der Waals | Weak | Methane, Butane, Propane | All molecules do this. |
You can tell that a molecule is polar if it has atoms with very different electronegativities and it is asymmetrical. Atoms on the right side of the periodic table are very electronegative. Atoms on the left are very electropositive.
Chemists often use intermolecular forces to separate and purify chemicals. For example, they often use nonpolar solvents to extract nonpolar chemicals from plants.
Solubility
Compounds dissolve other compounds that have similar intermolecular forces. A polar compound that can hydrogen bond will dissolve other polar compounds that can hydrogen bond.
The number that tells you how well something will dissolve is called Ksp. The higher the Ksp is, the more soluble the compound will be.
Thermodynamics
A reaction that gives off heat energy is exothermic. Exothermic reactions have a negative DH. That means that heat is leaving them.
A reaction that sucks up heat is endothermic. Endothermic reactions have a positive DH. That means that heat is getting sucked up and used by them.
Entropy is how disordered something is. If your room is messy, it has a high entropy. A well folded protein has a low entropy. An unfolded, denatured, protein has a high entropy.
Free energy is a measure of how stable something is. The more energy something has, the less stable it is. Aromatic compounds like benzene are very stable. A negative Gibbs Free Energy means a reaction is spontaneous. G is Gibbs free energy. H is enthalpy. T is temperature in degrees Kelvin. S is entropy.
G = DH - TDS
Kinetics
The speed of the reaction is called the reaction kinetics. A catalyst is a chemical that can lower the activation energy of a reaction without being used up during the reaction. That makes the reaction go much faster, because the molecules do not need to go over as high of an energy barrier. Most catalysts are organometallic compounds. That means they have organic ligands and a metal center.
Reactions go faster at high temperatures because it is easier for them to get over the energy barrier. In other words, at higher temperatures, they have enough energy to easily get above the activation energy.
Ziegler-Natta catalysts are used to make polyethylene and polypropylene. Polymerization is a reaction that turns a monomer, a small molecule, into a polymer, a huge molecule that is a chain of lots of small molecules. Polyethylene and Polypropylene are plastics that are often used for food and drink containers.
Palladium on carbon is used as a hydrogenation catalyst. It adds hydrogen to unsaturated molecules. Unsaturated molecules have double or triple bonds.Modern Ways to Identify Molecules
This is Analytical Chemistry!
Mass Spectrometry MS
Mass spectrometry means breaking a compound into little pieces then measuring the weights of the pieces to figure out what that compound is. The first step is called ionization, this means zapping the compound with electrons, hot gas, or a laser to make it jump up into a vacuum tube. The next step is detection, this is done by measuring how fast the fragments are moving or how far they are deflected by an electromagnet.
Nuclear Magnetic Resonance NMR
Protons and electrons both have what physicists call spin. If you put a chemical into a really strong magnet all of the protons will spin in the same direction. If you then shoot it with radio waves, you can get all of the protons to flip sideways. If you measure how fast the protons flip back to spinning in their original direction, then do some fancy math called a Fourier transform, you get an NMR spectrum. The NMR spectrum tells you how deshielded the protons are. In other words, it tells you if there are any functional groups in the molecule that withdraw electrons. Groups that deshield a proton by pulling electrons away from it have different strengths. You can tell what they are by how strongly they shift the proton signals to the left.
NMR can be done with any nucleus that has an odd number of protons. Hydrogen NMR is called 1H NMR. The second most common type of NMR is Carbon 13 NMR, which is also called 13C NMR. Since 13C is not the most common isotope of carbon, it takes a long time to get a good carbon spectrum.
When you go to the hospital to get an MRI, what the machine is actually doing is running a 1H NMR spectrum of your whole body.
Fourier Transform Infrared Spectroscopy FTIR
Raman Infrared Spectroscopy
UV-Vis Spectroscopy UV-VIS
By measuring how much light a chemical absorbs at many different wavelengths, that chemical can be identified. Different chemical bonds vibrate at different frequencies. By measuring how much light a chemical absorbs at each wavelength gives information about what types of chemical bonds are present in the molecule.
X-ray Diffraction
First, the scientist grows a crystal. Then she puts the crystal into a machine called an x-ray diffractometer. A beam of x-rays is shot through the crystal. This creates a diffraction pattern. Computers can be used to do some fancy math called a Fourier transform to turn a diffraction pattern into a 3D picture of the crystal.
Immunochemistry
Antibodies are y shaped proteins that will stick strongly to one and only one molecule. These are often used to identify other proteins. ELISA, dot blots, and western blots, are all forms of immunochemical detection. Biochemists often use these methods.
Atomic Absorption
A special machine burns a tiny amount of the chemical then measures exactly wavelengths of light are given off by the flame.
Old Fashioned Ways To Identify Molecules
Thin Layer Chromatography TLC
This is a low tech, old school, way to identify compounds and check their purity. A spot of the compound is put onto some special paper. The bottom of the paper is then dipped into a solvent. Different compounds will travel up the paper at different speeds. If more than one spot shows up, the compound is not pure. The distance the spot traveled divided by the distance the solvent traveled is called the Rf value.
This is an old method, but scientists still use it all the time because it is very fast and cheap. It is often done to see if a chemical reaction is over. If the spot that corresponds to the starting material is still there, then the reaction is not over.
Index of Refraction
How fast light travels in a substance is the index of refraction. The index of refraction is also how far light will bend to the side when it passes through that substance. By coating a glass surface with some of the substance, then measuring the angle that the light passing through that substance bends, you can measure its
Melting Point
The melting point of chemicals is measured by putting them in a tiny sealed glass tube called a capillary. If the substance is not pure, it will melt at a lower temperature. These days, a fancy modern machine called a differential scanning calorimeter is also used to measure melting points. There are also machines that will record a little video clip of the chemical melting in the glass tube.
Specific Gravity
The density of a substance is another clue to the identity. First weigh it, then divide the mass by the volume. Another name for density is specific gravity.
Flame Test
Some elements will turn a flame different colors when burned. By burning a small amount of a chemical, you can get an idea of what elements are in it. This is basically a ghetto version of atomic absorption spectroscopy.
Smell
Smelling an unknown chemical can be very dangerous, but some chemicals are easily identifiable by their smells. Chemicals with a thiol functional group, that means an SH, are very stinky. So are amines and most aldehydes. If you know what a thiol smells like, you can identify them instantly.
Mass Spectrometry MS
Mass spectrometry means breaking a compound into little pieces then measuring the weights of the pieces to figure out what that compound is. The first step is called ionization, this means zapping the compound with electrons, hot gas, or a laser to make it jump up into a vacuum tube. The next step is detection, this is done by measuring how fast the fragments are moving or how far they are deflected by an electromagnet.
Nuclear Magnetic Resonance NMR
Protons and electrons both have what physicists call spin. If you put a chemical into a really strong magnet all of the protons will spin in the same direction. If you then shoot it with radio waves, you can get all of the protons to flip sideways. If you measure how fast the protons flip back to spinning in their original direction, then do some fancy math called a Fourier transform, you get an NMR spectrum. The NMR spectrum tells you how deshielded the protons are. In other words, it tells you if there are any functional groups in the molecule that withdraw electrons. Groups that deshield a proton by pulling electrons away from it have different strengths. You can tell what they are by how strongly they shift the proton signals to the left.
NMR can be done with any nucleus that has an odd number of protons. Hydrogen NMR is called 1H NMR. The second most common type of NMR is Carbon 13 NMR, which is also called 13C NMR. Since 13C is not the most common isotope of carbon, it takes a long time to get a good carbon spectrum.
When you go to the hospital to get an MRI, what the machine is actually doing is running a 1H NMR spectrum of your whole body.
Fourier Transform Infrared Spectroscopy FTIR
Raman Infrared Spectroscopy
UV-Vis Spectroscopy UV-VIS
By measuring how much light a chemical absorbs at many different wavelengths, that chemical can be identified. Different chemical bonds vibrate at different frequencies. By measuring how much light a chemical absorbs at each wavelength gives information about what types of chemical bonds are present in the molecule.
X-ray Diffraction
First, the scientist grows a crystal. Then she puts the crystal into a machine called an x-ray diffractometer. A beam of x-rays is shot through the crystal. This creates a diffraction pattern. Computers can be used to do some fancy math called a Fourier transform to turn a diffraction pattern into a 3D picture of the crystal.
Immunochemistry
Antibodies are y shaped proteins that will stick strongly to one and only one molecule. These are often used to identify other proteins. ELISA, dot blots, and western blots, are all forms of immunochemical detection. Biochemists often use these methods.
Atomic Absorption
A special machine burns a tiny amount of the chemical then measures exactly wavelengths of light are given off by the flame.
Old Fashioned Ways To Identify Molecules
Thin Layer Chromatography TLC
This is a low tech, old school, way to identify compounds and check their purity. A spot of the compound is put onto some special paper. The bottom of the paper is then dipped into a solvent. Different compounds will travel up the paper at different speeds. If more than one spot shows up, the compound is not pure. The distance the spot traveled divided by the distance the solvent traveled is called the Rf value.
This is an old method, but scientists still use it all the time because it is very fast and cheap. It is often done to see if a chemical reaction is over. If the spot that corresponds to the starting material is still there, then the reaction is not over.
Index of Refraction
How fast light travels in a substance is the index of refraction. The index of refraction is also how far light will bend to the side when it passes through that substance. By coating a glass surface with some of the substance, then measuring the angle that the light passing through that substance bends, you can measure its
Melting Point
The melting point of chemicals is measured by putting them in a tiny sealed glass tube called a capillary. If the substance is not pure, it will melt at a lower temperature. These days, a fancy modern machine called a differential scanning calorimeter is also used to measure melting points. There are also machines that will record a little video clip of the chemical melting in the glass tube.
Specific Gravity
The density of a substance is another clue to the identity. First weigh it, then divide the mass by the volume. Another name for density is specific gravity.
Flame Test
Some elements will turn a flame different colors when burned. By burning a small amount of a chemical, you can get an idea of what elements are in it. This is basically a ghetto version of atomic absorption spectroscopy.
Smell
Smelling an unknown chemical can be very dangerous, but some chemicals are easily identifiable by their smells. Chemicals with a thiol functional group, that means an SH, are very stinky. So are amines and most aldehydes. If you know what a thiol smells like, you can identify them instantly.
How Scientists Measure The Concentration of Solutions
This is analytical chemistry!
Titrations
This is by far the most old school method for measuring the concentration of something in a liquid. The scientist prepares a solution of something that reacts with the other compound and then adds it drop by drop until there is a color change or other easy to recognize event that means the reaction is over. When the reaction is over, we call that the equivalence point. It is the time when amount of the known compound is equal to the amount of the unknown compound. Since the scientist knows how much of the unknown compound was added, some easy math can be used to calculate the concentration of the unknown. A classic example of this is done with acids and bases.
A scientist wants to know the concentration of acetic acid in a bottle of vinegar so she adds a drop of indicator to the vinegar then titrates 100mL of the vinegar with 0.1M sodium hydroxide until the equivalence point is reached. Once the equivalence point has been reached, she knows how much NaOH was used to neutralize the acetic acid, so she can easily calculate the concentration of acetic acid in the vinegar.
Doctors sometimes say that they are titrating a patient onto a medication. That is a fancy way of saying that they give the patient a little bit more medicine each day until they have found the right dose.
Spectrophotometry and UV-Vis Spectrometry
If you are making fruit punch, and you add water to it, the color of your beverage will not be as dark.
Beer’s law says that the amount of light a liquid absorbs is directly related to it’s concentration. So if you can use a machine to measure how much light does not make it through a sample of the liquid, you can easily calculate the concentration. Not all chemicals absorb light at every wavelength.
Biochemists use a spectrophotometer to check the concentration and purity of DNA and Protein solutions every day. Proteins absorb UV radiation at 280nm and DNA absorbs at 260nm. By calculating the ratio of absorbance at 260nm and 280nm, the purity of DNA or protein can be determined. Biochemists do this all the time.
High Performance Liquid Chromatography HPLC
Just about every drug company in the country hires a ton of people to do HPLC for them. This method of measuring concentrations uses a high pressure pump to squirt liquid through a little column. In that column, each compound travels at a different speed. Every compound comes out of the column at a different time. A detector, usually a spectrophotometer or a mass spectrometer, can then tell you how much stuff came out of the column. This method of analysis requires a calibration curve.
Gas Chromatography GC
This works the same way as liquid chromatography, but only for volatile compounds. That usually means compounds with a molecular weight below 500 and a low boiling point.
Titrations
This is by far the most old school method for measuring the concentration of something in a liquid. The scientist prepares a solution of something that reacts with the other compound and then adds it drop by drop until there is a color change or other easy to recognize event that means the reaction is over. When the reaction is over, we call that the equivalence point. It is the time when amount of the known compound is equal to the amount of the unknown compound. Since the scientist knows how much of the unknown compound was added, some easy math can be used to calculate the concentration of the unknown. A classic example of this is done with acids and bases.
A scientist wants to know the concentration of acetic acid in a bottle of vinegar so she adds a drop of indicator to the vinegar then titrates 100mL of the vinegar with 0.1M sodium hydroxide until the equivalence point is reached. Once the equivalence point has been reached, she knows how much NaOH was used to neutralize the acetic acid, so she can easily calculate the concentration of acetic acid in the vinegar.
Doctors sometimes say that they are titrating a patient onto a medication. That is a fancy way of saying that they give the patient a little bit more medicine each day until they have found the right dose.
Spectrophotometry and UV-Vis Spectrometry
If you are making fruit punch, and you add water to it, the color of your beverage will not be as dark.
Beer’s law says that the amount of light a liquid absorbs is directly related to it’s concentration. So if you can use a machine to measure how much light does not make it through a sample of the liquid, you can easily calculate the concentration. Not all chemicals absorb light at every wavelength.
Biochemists use a spectrophotometer to check the concentration and purity of DNA and Protein solutions every day. Proteins absorb UV radiation at 280nm and DNA absorbs at 260nm. By calculating the ratio of absorbance at 260nm and 280nm, the purity of DNA or protein can be determined. Biochemists do this all the time.
High Performance Liquid Chromatography HPLC
Just about every drug company in the country hires a ton of people to do HPLC for them. This method of measuring concentrations uses a high pressure pump to squirt liquid through a little column. In that column, each compound travels at a different speed. Every compound comes out of the column at a different time. A detector, usually a spectrophotometer or a mass spectrometer, can then tell you how much stuff came out of the column. This method of analysis requires a calibration curve.
Gas Chromatography GC
This works the same way as liquid chromatography, but only for volatile compounds. That usually means compounds with a molecular weight below 500 and a low boiling point.
Careers in Chemistry
| Level of Education | Starting Salary | Years of College |
| B.S. in Chemistry | $45,000 – 50,000 per year | 4 |
| M.S. in Chemistry | $55,000 – 65,000 per year | 4+2 |
| PhD. in Chemistry | $65,000 – 95,000 per year | 4+5 |
| B.S. Chemistry + M.D. | $100,00 – 300,000 per year | 4+4 |
| B.S. Chemistry + J.D. | $40,000 – 125,000 per year | 4+3 |
| B.S. Materials Science | $45,000 – 50,000 per year | 5 |
| M.S. Materials Science | $55,000 – 65,000 per year | 5+1 |
| Ph.D. Materials Science | $65,000 – 95,000 per year | 4+5 |
| B.S. Chemical Engineering | $50,000 – 55,000 per year | 5 |
| M.S. Chemical Engineering | $60,000 – 70,000 per year | 5+1 |
| Ph.D. Chemical Engineering | $80,000 – 100,000 per year | 4+5 |
College Chemistry Classes
Freshman Year General Chemistry
Sophomore Year Organic Chemistry
Junior Year Physical Chemistry and Biochemistry or Analytical Chemistry
Senior Year Special Topics in Chemistry, Drug Design, Genetics, Research,
Protein Crystallography, Polymers, Materials Science
Pre-med, pre-pharmacy, pre-veterinary, and pre-dental students must take general chemistry and organic chemistry. Most of them choose to take biochemistry because it will help them out a lot when they take the MCAT and when they become doctors.
Organic Chemists
In industry, organic chemists make new chemicals that have never been made before. They also try to find cheaper or safer ways to make large amounts of super expensive chemicals. Most organic chemists work in the pharmaceutical industry. Some work in the semiconductor industry or petroleum industry. Physical organic chemists try to figure out how chemical reactions work.
Biochemists
Most biochemists work in the pharmaceutical industry. Some of them express and purify huge amounts of proteins, others study the effects that new drug candidates have on cells or animals. Many other biochemists work in healthcare. Perhaps the fastest growing industry in California is the biopharmaceutical industry. Biopharmaceuticals are drugs made from biological materials like protein, DNA, RNA, and lipids.
Analytical Chemists
Lots of analytical chemists do quality control work. This means that they use a bunch of fancy instruments like HPLC and GC-MS to make sure that the chemicals their company produces are pure. If a batch of drugs or food has something poisonous in it, the quality control chemist will make sure it is destroyed so that nobody will get poisoned or buy an ineffective product.
Materials Scientists
The core concept of materials science is understanding how the structure of a material controls its properties. Most materials science people work in the semiconductor or defense industry, but recently a lot of pharmaceutical companies want to hire them to make materials for drug delivery. Computer chips contain lots of really fancy materials that must be processed by special methods like chemical vapor deposition, etching, and lithography. You will learn about this when we watch the documentary Silicon Run.
A materials scientist might do the following.
- Discover new materials. Metals for knives, Plastic for car parts, Semiconductors for computer chips, Liposomes for gene therapy, Composites for fighter planes.
- Figure out how to process materials, this means heat treating them, squishing them, polishing them, and doing other things to make them work better.
Chemical Engineers
Chemical engineers usually
- Do process control, which means writing the computer programs that keep a chemical reactor running.
- They design chemical reactors.
- Find ways to scale up reactions, that means they figure out the cheapest way to make a lot of something.
Patent Lawyers
Intellectual property law is about protecting the rights of inventors, scientists, and artists. Patent lawyers file a report with the federal government explaining that their client was the first person to invent a new product or method for doing something. If someone else tries to steal their idea, the patent lawyer will sue them. If someone wants to buy their idea, the patent lawyer will write a licensing contract. To become a patent lawyer, you must earn a science or engineering degree, then go to law school. At the moment, it is very easy to find a job if you are a good patent lawyer. Many experienced patent lawyers make 300 dollars an hour.
Subscribe to:
Posts (Atom)