The Handy Chemistry Answer Book. Justin P. LomontЧитать онлайн книгу.
solvent is a liquid (though it can be a gas or a solid, but forget about that for now) that other chemicals are dissolved in. These other chemicals can be called the solute. The solute and the solvent can together be called a solution. Take salt water: water is the solvent, salt is the solute, and we can refer to the salt water as a solution.
What makes something magnetic?
As we mentioned just briefly above, electrons have a property called a spin, or spin angular momentum, which can take on two possible values. This property, combined with the fact that electrons are charged particles, dictates that each electron has an associated magnetic moment, called the spin magnetic moment. In a macroscopic object, magnetism, or lack thereof, is determined by whether these spin magnetic moments are all aligned in the same direction. If all of the spin magnetic moments line up in the same orientation, the object will behave as a magnet. If the spin magnetic moments are oriented randomly, the object won’t be magnetic. The trick is that only certain materials have the potential to exhibit magnetism, and we’ll get to that next.
What determines which metals can be magnetized?
Chemists discuss magnetism in terms of three basic categories: diamagnetism, paramagnetism, and ferromagnetism.
Diamagnetic materials have all of their electrons arranged in pairs, which, by definition, means that their spin magnetic moments must all be arranged in pairs and thus cancel each other out. For this reason, diamagnetic materials cannot be magnetic, and won’t be influenced by magnetic fields.
Paramagnetic materials have unpaired electrons, but in these materials the electrons’ spin magnetic moments cannot all be lined up in the same direction, which means that they cannot be strongly magnetic. Since they do have unpaired electrons, they can be influenced by applied magnetic fields, but not to the same extent as the third class, ferromagnetic materials.
Ferromagnetic materials are the materials that can give rise to the magnets we’re all familiar with. All of the materials that magnets can interact strongly with are ferromagnetic. In these materials, there are unpaired electrons whose magnetic spin can all be aligned in the same direction. Note that just because a material is ferromagnetic doesn’t mean it must be a magnet, but rather just that it has the potential to be magnetized. Take a paper clip, for example; when you first pick it up it’s not a magnet, but you can turn it into a weak magnet by holding a magnet next to it for a short length of time. Some of the most common ferromagnetic substances are those made of iron, nickel, or cobalt.
What is an ideal gas?
An ideal gas is a collection of atoms or molecules that do not interact with one another and occupy essentially no volume. While this is an idealized model, it turns out to describe many gases very well. The reason it works so well is that the atoms or molecules making up a gas are spread out far from one another so that the intermolecular forces between them are extremely weak (they don’t “feel” each other). This description leads to the ideal gas law, which is a relationship between the pressure, volume, and temperature of a gas. The ideal gas law allows chemists to predict how, for example, the volume of a gas will change as its temperature is increased. The equation for the ideal gas law is
PV = NkbT
where P is pressure, V is volume, N is the number of particles (atoms or molecules), T is temperature, and kb is Boltzmann’s constant (a fundamental physical constant).
How many different chemical substances have been discovered?
According to the Chemical Abstracts Service (CAS), which is the world’s largest authority for chemical information, the seventy millionth chemical compound was recently registered (announced December 2012). Today, new chemicals are being discovered and registered at a staggering rate: the sixty millionth chemical was registered only eighteen months earlier!
MACROSCOPIC PROPERTIES: THE WORLD WE SEE
PHASES OF MATTER AND INTENSIVE PROPERTIES
What are the different phases of matter?
There are three phases, or states, of matter that you come across every day—solids, liquids, and gases. There is a fourth phase of matter, plasma, which is only naturally found in stars and elsewhere in outer space. The distinctions between the first three phases are usually made using bulk properties. Solids have a defined shape and volume, while liquids easily change their shape but not their volume. Gases have neither a defined shape nor volume.
What is plasma?
Plasma, the fourth state of matter, is a gas where some amount of the particles have been ionized. As little as 1% ionization leads to very different properties for plasmas than gases, including increased conductivity (like lightning) and magnetization.
Are there plasmas in our daily lives?
Plasmas are found in fluorescent lights and neon lights. If you’ve ever seen a Tesla coil at a science museum, the arcs of light that they produce are plasma, as is lightning. Plasma TVs and plasma lamps are correctly named—both generate light using plasma, similar to fluorescent lights.
What is a phase diagram?
A phase diagram shows the phases of a particular substance as a function of temperature and pressure. An example for a single component phase diagram (as in not a mixture) is shown above. Phase diagrams also exist for mixtures, but these get very complicated very quickly.
A phase diagram shows the phases of a particular substance as a function of temperature and pressure.
What is a triple point?
The temperature and pressure at which three phases of a substance are in equilibrium is known as a triple point. The three phases can be solid, liquid, and gas, but can also be two solid phases (different arrangements of the molecules in the solid) and a liquid phase.
What is a critical point?
A critical point is a combination of temperature and pressure values above which a phase boundary no longer exists. There are liquid-liquid critical points above which the two liquid phases become miscible, and also liquid-gas critical points above which the boundary between the liquid and gas phases disappears and the substance becomes supercritical.
What is a supercritical fluid?
Above its critical point, a given temperature and pressure combination, a substance behaves like both a liquid and a gas and is called supercritical. Supercritical fluids are very good solvents, like liquids, and as a result many modern chemical processes use them.
How is coffee decaffeinated?
Consider the chemistry required to decaffeinate coffee. Most techniques use an extraction process to remove the caffeine from the green coffee beans before they are roasted. One method starts by steaming the green beans and then rinsing them with an organic solvent (usually dichloromethane) to pull the caffeine molecules out of the beans. The other method uses supercritical carbon dioxide to extract caffeine. The latter obviously avoids the use of toxic solvents, but is energy-intensive. With all extraction techniques, it is challenging to only remove the caffeine and not the flavor compounds that we want to taste in our coffee.
How many phases can be in coexistence?
A rule called the Gibbs phase rule tells us how many phases can be in coexistence for a given substance or mixture. The rule arises from the fact that, to be in coexistence, a constraint exists that the chemical potentials of each