If you had a choice between a glass of lemon juice or apple juice, most folks would pick the sweeter one – apple. Did you know that apples are loaded with malic acid, and are actually considered to be acidic? It’s just that there is so much more sugar in an apple than a lemon that your taste buds can be fooled. Here’s a scientific way (which is much more reliable) to tell how acidic something is.

Acids are sour tasting (like a lemon), bases are bitter (like unsweetened cocoa powder). Substances in the middle are more neutral, like water. Scientists use the pH (power of hydrogen, or potential hydrogen) scale to measure how acidic or basic something is. Hydrochloric acid registers at a 1, sodium hydroxide (drain cleaner) is a 14. Water is about a 7. pH levels tell you how acidic or alkaline (basic) something is, like dirt. If your soil is too acidic, your plants won’t attract enough hydrogen, and too alkaline attracts too many hydrogen ions. The right balance is usually somewhere in the middle (called ‘pH neutral’). Some plants change color depending on the level of acidity in the soil – hydrangeas turn pink in acidic soil and blue in alkaline soil.

There are many different kinds of acids: citric acid (in a lemon), tartaric acid (in white wine), malic acid (in apples), acetic acid (in vinegar), and phosphoric acid (in cola drinks). The battery acid in your car is a particularly nasty acid called sulfuric acid that will eat through your skin and bones. Hydrochloric acid is found in your stomach to help digest food, and nitric acid is used to make dyes in fabrics as well as fertilizer compounds.

Click here to go to next lesson on Gravimetric Calculations.

The kinetic theory of gases assumes that all gases behave ideally, but we know that’s not really what happens in the real world. For example, real gas particles do occupy space and also attract each other, although these properties are more apparent at lower temperature because usually the particles have enough kinetic energy to zip by each other without worrying about the attractive or repulsive charges from other molecules. If the molecules move slow enough though, they do get affected by the push or pull of other molecules.

Also at high pressures, the molecules are so tightly packed together that they do start to have volume considerations that need to be addressed. So for a real gas, we can make calculations like this:

The kinetic theory of gases relates what’s going on with the motion of the tiny invisible molecules with the properties you can measure, like temperature and pressure. Kinetic means the study of motion, and for us, it’s the motion of the gas molecules.

Atoms are held together by bonds, and bonds take energy, so an atom that is bonded has less energy than if it was free floating around on its own. Energy is required to break a bond (bond energy). Energy is released when a bond is created. (We’ll use this idea again later when we talk about Lewis Dot structures.) Each molecule has its own bond energy which you can look up in a table in your chemistry book. For example, C-H bonds take about 100kcal of energy to break 1 mol of C-H bonds, so you’ll find bond energies listed in kcal per mol. If you look up C-C bonds, you’ll find 80 kcal/mol. And a double C-C bond is 145 kcal per mol.

This is a cool video from a Teacher’s Educational Channel in Europe I thought you might enjoy about the science of fireworks:

You can view the full video here: https://www.youtube.com/watch?v=3hNf8DRg5vQ

The “mean free path” is the average distance a gas molecule travels between collisions. If a molecule has a diameter “d”, then the effective cross section for a collision is “π d²“. This is used mostly with the Kinetic Theory of Gases, and is a good estimation of how particles move in a gas.
Please login or register to read the rest of this content.

Graham’s law tells is how gases move through porous materials, like air in a balloon. Ever noticed how balloons don’t stay inflated forever? That’s because the gas diffuses through the balloon skin itself. And if you take a good look, helium balloons deflate the next day, whereas normal air balloons will keep for a few days. Small helium molecules effuse through the tiny holes in the balloon skin much faster than normal air does.
Please login or register to read the rest of this content.

Avogadro’s Law states that 1 mole of every gas occupies the same volume at the same temperature and pressure. The mass of the gas might be different… one mole of helium is going to weigh less than one mole of nitrogen, for example, but the number of helium gas molecules is exactly the same as the number of nitrogen molecules, and both of them will occupy the same amount of space (22.4L) at standard temperature and pressure. At room temperature and pressure, it’s slightly higher (24 L).
Please login or register to read the rest of this content.

Gravimetric analysis is a technique through which the amount of the ion being analyzed can be determined through the measurement of mass. Gravimetric analysis depend on comparing the masses of two compounds containing the ion to be analyzed. Here’s an example:

A 3.46 g sample of limestone(CaCO3 ) was dissolved in 0.1M (HCl) solution like this:

Wa-hoo! You’ve completed the entire Chemistry Course!

Imagine a plate of spaghetti. The noodles slide around and don’t clump together, just like the long chains of molecules (called polymers) that make up slime. They slide around without getting tangled up. The pasta by itself (fresh from the boiling water) doesn’t hold together until you put the sauce on. Slime works the same way. Long, spaghetti-like chains of molecules (called polymers) don’t clump together until you add the sauce – something that cross-links the molecule strands (polymer) together.
Please login or register to read the rest of this content.

Potassium perchlorate is usually safer than chlorate salt, but it sometimes is hard to get it. In the past, the only supplier in the US makes ammonium perchlorate, the oxidizer that was used with the space shuttle booster rockets, and each shuttle launch required 1.5 million pounds of it, which was twice the annual consumption rate, so when there were a lot of shuttle launches, the fireworks market took a hit and it was near impossible to get any potassium perchlorate.
Please login or register to read the rest of this content.

Chemists want to control not only what comes out of a chemical reaction, but how fast the reaction occurs. For example, scientists are working to slow down the depletion rate of the ozone in the upper level of our atmosphere, so we stay protected from harmful UV rays.

The rate of the chemical reaction of a nail rusting is slow compared to how fast baking soda reacts with vinegar. Different factors affect the speed of the reaction, but the main idea is that the more collisions between particles, the faster the reaction will take place.
Please login or register to read the rest of this content.

Hydrolysis is a chemical reaction that happens when a molecule splits into two parts when water is added. One part gains a hydrogen (H+) and the other gets the hydroxyl (OH–) group. The reaction in the experiment forms starch from glucose, and when we add water, it breaks down the amino acid components just like the enzymes do in your stomach when they digest food.

Displacement: There are several different types of displacement reactions, including single, double, and acid-base.
An example of a single substitution reaction (A + BC  AC + B) occurs when zinc combines with hydrochloric acid. The zinc replaces the hydrogen:Zn + 2 HCl  ZnCl2 + H2

This reaction happens when simple compounds come together to form a more complicated compound.

The iron (Fe) in a nail combines with oxygen (O2) to form rust, also called iron oxide (Fe2O3).
2Fe + O2  Fe2O3

We’re about to do a synthesis reaction with sulfur. Sulfur is element #6 on the periodic table. Sulfur is used in fertilizer, black powder, matches, and insecticides. In pioneer times sulfur was put into patent medicines and used as a laxative.
Please login or register to read the rest of this content.

A combustion reaction gives off energy, usually in the form of heat and light.  The reaction itself includes oxygen combining with another compound to form water, carbon dioxide, and other products.

A campfire is an example of wood and oxygen combining to create ash, smoke, and other gases. Here’s the reaction for the burning of methane (CH4) which gives carbon dioxide (CO2) and water (H2O):
CH4 + 2 O2  CO2 + 2 H2O
Please login or register to read the rest of this content.

If you guessed that electrochemistry has to do with electricity and chemistry, you’re right! But you might wonder how they work together. Back in 1800, William Nicholson and Johann Ritter were the first ones to split water into hydrogen and oxygen using electrolysis. (Soon afterwards, Ritter went on to figure out electroplating.) They added energy in the form of an electric current into a cup of water and captured the bubbles forming into two separate cups, one for hydrogen and other for oxygen.
Please login or register to read the rest of this content.

Chemical equilibrium is the condition that happens when the concentration of the reactants and products don’t have any net change over time. This doesn’t mean that the reaction stops, just that the producing and consuming of the molecules is in balance.

Most chemical reactions are reversible, just like phases changes. Do you remember the hot icicle experiment? Do you remember how to get it back to the starting point? You have to add energy to the solid sodium acetate to turn it back into a liquid, so it can turn back into a solid again. Then let that experiment sit for a bit (overnight or about 12 hours) and in the morning, you’ll have crystals growing on your pipe cleaner. Now if you want to reverse this reaction, all you have to do is add energy to the system and the crystals will dissolve back into the solution. You can heat it up in the microwave or in a pot of water on the stove, and the crystals will disappear.
Please login or register to read the rest of this content.

Plasma makes up a very large percentage of the matter in the universe. Not much of it is on Earth and the plasma that is here is very short lived or stuck in a tube. Plasma is basically what happens when you add enough energy to a gas that the atoms move and vibrate around so energetically that they smack into each other and rip electrons off each other, so you have positively charged atoms (called ions) that lost their electrons, and also the electrons themselves which are negatively charged, all zinging around in the gas.
Please login or register to read the rest of this content.

Solids
What makes the solids, liquids, gases etc. different is basically the energy (motion) of the atoms. From BEC, where they are so low energy that they are literally blending into one another, to plasma, where they are so high energy they can emit light. Solids are the lowest energy form of matter that exist in nature (BEC only happens under laboratory conditions).

In solids, the atoms and molecules are bonded (stuck) together in such a way that they can’t move easily. They hold their shape. That’s why you can sit in a chair. The solid molecules hold their shape and so they hold you up. The typical characteristics that solids tend to have are they keep their shape unless they are broken and that they do not flow.

A liquid has a definite volume (meaning that you can’t compress or squish it into a smaller space), but takes the shape of its container. Think of a water-filled balloon. When you smoosh one end, the other pops out. Liquids are generally incompressible, which is what hydraulic power on heavy duty machinery (like excavators and backhoes) is all about.

Here are the most important things about gases to remember:

• Gases assume the shape and volume of their container.
• Gases have lower densities than their solid or liquid phases.
• Gases are more easily compressed than their solid or liquid phases.
• Gases will mix completely and evenly when confined to the same volume.
• All elements in Group VIII are gases. These gases are known as the noble gases.
• Elements that are gases at room temperature and normal pressure are all nonmetals.

By knowing the value of the bond energy, we can predict if a chemical reaction will be exothermic or endothermic. If the bonds in the products are stronger than the bonds in the reactants, then the products are more stable and the reaction will give off heat (exothermic).

Exothermic chemical reactions release energy as heat, light, electrical or sound (or all four). Usually when someone says it’s an exothermic reaction, they usually just mean energy is being released as heat.

Some release heat gradually (for example, a disposable hand-warmer), while others are more explosive (like burning magnesium). The energy comes from breaking the bonds within the chemical reaction.

A molecule is the smallest unit of a compound that still has the compound’s properties attached to it. Molecules are made up of two or more atoms held together by covalent bonds.

In the space where electrons from different atoms interact with each other, chemical bonds form. The electrons in the outermost shell are the ones that form the bonds with other atoms.

When the atoms share the electron(s), a covalent bond is formed. Electrons aren’t perfect, though, and usually an electron is more attracted to one atom than another, which forms a polar covalent bond between atoms (like in water, H2O).

While it may seem a bit random right now, with a little bit of study, you’ll find you can soon understand how molecules are formed and the shapes they choose once you figure out the types of bonds that can form.

There are different kinds of bonds that can form in a molecule. When two atoms approach each other close enough for their electron clods to interact, the electrons of one repels the electrons in the other, and the same thing happens within the nucleus of the atoms. At the same time, each atom’s negatively charged electron is attracted to the other atom’s positively charged nucleus. If the atoms still come closer, the attractive forces offset the repulsive and the energy of the atom decreases and bonds are formed – the atom sticks together. When the energy decrease is small, the bonds are van der Waals. When the energy decrease is larger, we have chemical bonds, either ionic or covalent.

You’re going to try to determine what is happening during the flame test when you see different colors. Think about what particles are found in the chemicals you’re using, and why the different chemicals emit different colors of light? Where else have you seen colorful light emissions?

Did you aim your razor slit at a light source such as a fluorescent light, neon sign, sunset, light bulb, computer screen, television, night light, candle, fireplace… ? Make sure that the diffraction grating does right up to your eye.  Move the spectrometer around until you can get the rainbow to be on the scale inside the tube.

Once you’ve got the hang of it, you might be wondering, wow – cool… but what am I looking at exactly? Ok – so those lines you saw inside the tube – those are spectral lines. Can you see how there are brighter lines? Which frequencies are those? Well we need a ruler to measure those. Can you see how if we lined up a ruler as could tell what the frequencies are?

Energy can take one of two forms: matter and light (called electromagnetic radiation). Light is energy that can travel through space. When you feel the warmth of the sun on your arm, that’s energy from the sun that traveled through space as infrared radiation (heat). When you see a tree or a bird, that’s light from the sun that traveled as visible light (red, orange… the whole rainbow) reflecting and bouncing off objects to get to your eye. Light can travel through objects sometimes… like the glass in a window.

Light can take the form of either a wave or a particle, depending on what you’re doing with it. It’s like a reversible coat – fleece on the inside, windbreaker on the outside. It can adapt to whatever environment you put it in.
Please login or register to read the rest of this content.

One of the dreams of early chemists was to figure out how to transform lead into gold. Lead has 82 protons in its core whereas gold contains only 79. So conceivably all you’d need to do is remove three protons and presto! So how do you do that? Since protons can’t be stripped off with a chemical reaction, you need to smack it hard with something to knock off just the right amount. Lead, however, if a very stable element, so it’s going to require a lot of energy to remove three protons. How about a linear accelerator?

In a linear accelerator, a charged particle moves through a series of tubes that are charged by electrical and/or magnetic fields. The accelerated particle smacks the target, knocking free protons or neutrons and making a new element (or isotope). Glenn Seaborg (I actually met him!), 1951 Nobel Laureate in Chemistry, actually succeeded in transmuting a tiny quantity of lead into gold in 1980. He actually discovered (or helped discover) 10 elements on the periodic table, 100 new isotopes, and while he was still living (which usually doesn’t happen), they named an element after him (Seaborgium – 106).

Naturally radioactive elements emit energy without absorbing it first. Fluorescence for example – the atom absorbs a photon before emitting another photon. You have to “charge it up” or mix chemicals together before light comes out. With radioactive materials, they emit energy on their own, sometimes in the form of light, but sometimes they emit other particles. Let me explain.

Chemical reactions usually deal with only electron or atom exchanges. Nuclear reactions deal with changes inside the nucleus of an atom.
Please login or register to read the rest of this content.

Which one of these things you see on the screen now is radioactive? Most kids think that anything that glows must be radioactive, but it turns out that there’s a lot of things that glow that aren’t radioactive at all. Many minerals (called phosphors) glow after being exposed to sunlight which contains UV light. In 1897, Henri Becquerel was studying phosphorescence when he accidentally discovered radioactivity. Naturally radioactive elements emit energy without absorbing it first. Let me explain…

Cold light refers to the light from a glow stick, called luminescence. A chemical reaction (chemiluminescence) starts between two liquids, and the energy is released in the form of light. On the atomic scale, the energy from the reaction bumps the electron to a higher shell, and when it relaxes back down it emits a photon of light. Glow sticks generate light with very little heat, just like the glow you see from fireflies, jellyfish, and a few species of fungi. Chemiluminescence means light that comes from a chemical reaction.
Please login or register to read the rest of this content.

Okay, so now I want you to imagine a room full of ping pong balls that can bounce all by themselves. They go zipping all over the place all on their own. Now take those ping pong balls and add energy to them so now they bounce twice as fast. Got it?

Now what happens if we take away energy from them? Do they bounce slower? Yup!

Okay, now get them back to their original bouncing speed. Now take the room and make it smaller, like half it’s size, but keep the ping pong ball speed the same. Do they hit the walls more or less frequently? More! Are they speeding up or slowing down? Speeding up!

Find a low pressure (like the pressure you feel right now – it’s called 1 atm). Put your finder on the 1 mark on the vertical side (next to the “P”, which stands for Pressure) and follow the dashed line straight across. As you move across, so you notice how at low temperatures you’re in the ice region, but when you hit zero, you turn to water, and for temperatures below 100 deg C you’re only in the liquid water phase?

When something changes state, goes from like a liquid to a solid, all of the substance must change to the next state. For example, at 100° C all the water must change from a liquid to a gas. The temperature stays constant until it’s completely changed state. It’s kind of weird when you think about it.

If you were able to take the temperature of water as it changed from a solid (ice) to a liquid you would notice that the temperature stays at 32° F until that piece of ice was completely melted. The temperature would not increase at all.

Even if that ice was in an oven, the temperature would stay the same. Once all the solid ice had disappeared, then you would see the temperature of the puddle of water increase.
Please login or register to read the rest of this content.

Do you remember when I said that heat and temperature are two different things? Heat is energy – it is thermal energy. It can be transferred from one object to another.

Here’s what you do:

• Find your balloon.
• Put the balloon under the faucet and fill the balloon with a couple of tablespoons of water. Not too much!
• Now blow up the balloon and tie it, leaving the water in the balloon.
• You should have an inflated balloon with a tablespoon or two of water at the bottom of it.
• Have your adult helper carefully light the candle. Don’t do this next to your computer… do it in the sink.
• Hold the balloon over the candle carefully for a couple of seconds.
• Did it pop?

They can have a thermal energy but they can’t have heat. Heat is really the transfer of thermal energy. Or, in other words, the movement of thermal energy from one object to another.

If you put an ice cube in a glass of lemonade, the ice cube melts. Which way does heat flow?

The thermal energy from your lemonade moves to the ice cube.

The movement of thermal energy is called heat. The ice cube receives heat from your lemonade. Your lemonade gives heat to the ice cube.

Thermal energy is how much the molecules are moving inside an object. The faster molecules move, the more thermal energy it has.

Objects whose molecules are moving very quickly are said to have high thermal energy or high temperature. Like a cloud of steam, for example. The higher the temperature, the faster the molecules are moving.
Please login or register to read the rest of this content.

Energy is the capacity to do work or to transfer heat. You do work when you walk up a flight of stairs. You can feel the heat from the sun when you step in the sunlight. Both are energy.

Heat is associated with changing the temperature of an object. The temperature changes because energy is being transferred to it. Another word for heat is thermal energy.

Thermochemistry is the science of heat or thermal energy transfer and how to use it with chemical reactions.
Please login or register to read the rest of this content.

Your silver turns black because of the presence of sulfur in food. Here’s how the cleaning works: The tarnished spoon has silver sulfide on it, and when you put it in the solution, the silver sulfide combines with the baking soda and salt in the water solution to break apart into sulfur (which gets deposited on the foil) and silver (which goes back onto the spoon). Using the heat from your stove, you’ve just relocated the tarnish from the spoon to the foil. Just rinse clean and wipe dry!

The oxidation number of an element is the charge the atom has

I. For an atom in its elemental form the oxidation number is zero.
II. For any monatomic ion the oxidation number equals the charge of the ion.
III. For nonmetals the oxidation number is usually negative.
a) Oxygen is usually -2 in all compounds.
b) Fluorine is -1 in all compounds.
c) Hydrogen is +1 when bonded to nonmetals and -1 when bonded to metals (metal hydrides).
IV. The sum of the oxidation numbers for all atoms is zero for neutral
compounds or equals the charge for polyatomic ions.

Sterling silver is an alloy (a solid solution) of silver and copper. In order to find the percent of silver, you have to break it apart from the copper, which will make it an ion floating around in a liquid. Then you will need to bond it to something that will make it turn back into a solid so you can measure it.

In order to mix up chemicals in the right amounts (so we get the right amount out of the reaction), we have to figure out how much of a chemical to put in in the first place. Sometimes chemists have this problem: they need for example 2.0 L of 1.5 M solution of Na2CO3 (sodium carbonate). They find a bottle of Na2CO3 on the shelf, some distilled water, and a 2.00L flask. How much Na2CO3 do they put in the flask with the water?

Gas forming reactions are also exchange reactions. The best example I can think of for this type of reaction is what happens when you put a piece of chalk in a cup of vinegar. The chalk, which is mostly CaCO3 (calcium carbonate) and vinegar (acetic acid) forms calcium chloride and carbonic acid, which isn’t stable and quickly turns into water and carbon dioxide. A faster version of this experiment is what happens when you take an effervescent tablet, like alka seltzer, and stick it in water, because the tablet is actually a solid form of baking soda and vinegar put together. What happens when you mix baking soda and vinegar together?