Precipitate reactions are like watching a snow globe, but the snow appears out of nowhere.

For example, you can combine two liquid solutions that are totally clear and when you put them together, they each break apart into ions and then recombine in a way that looks like white snow in your test tube. Basically precipitate reactions make it possible to see the ions in a solution because they form a salt that’s not soluble – it doesn‘t dissolve in the solution. You can also get different colors of the precipitate snow, depending on which reactants you start out with. If you were to use potassium bromide (KBr) with silver nitrate, you’d find a yellowish snowstorm of silver bromide (AgBr).

When a substance is mixed with water it’s called an aqueous solution. Solubility is a property that a solid, liquid, or gases has when mixed with a solvent. If it can dissolve into the solvent, then it’s soluble. Dissolving marbles in water is a physical change. The marbles don’t break apart in the water to form new molecules with the water.

A reagent is chemical compound that creates a reaction in another substance; the product of that chemical reaction is an indicator of the presence, absence, or concentration of another substance.
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Let’s do a real example problem of how you’d do a calculation for figuring out how much oxygen you would need for the complete combustion of 454 grams of propane.
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A decomposition reaction breaks a complicated molecule into simpler ones usually by heating, but not always. In fact, if you leave a bottle of hydrogen peroxide on the counter, it decomposes into water (H2O) and oxygen (O2) without any heating at all. 2H2O  2O2 + 2H2

A very common type of decomposition is shown by the chemistry of metal carbonates. Calcium, one of the most abundant elements on earth, usually is locked up in limestone, called calcium carbonate. CaCO3. When heated to about 1000 degrees C, it decomposes to make lime (a solid metal oxide) and CO2 gas. Chemical engineers make more then 348 million tonnes of lime to make steel, cement and other chemicals.

If you have one element, like sulfur, which is S, and it’s a negative ion, just add “ide” to the end, like sulfide. Or if you have a carbon ion, it’s carbide. Nitrogen would be nitride, chlorine would be chloride.

If there’s more than one atom, especially if one of them is oxygen, then they have special names. The one with more oxygen atoms is the “ate” and the one with less is the “ite”. Sulfate has 4 oxygen atoms, and sulfite only has 3. Nitrate has three oxygen, and nitrite has only 2.

If there’s more than two ions, the one with the largest number of atoms gets the “per” and “ate”, like perchlorate. And the smallest one gets the “hypo” and “ite”, like hypochlorite.

A lot of chemical reactions happen in a solution (it allows the chemicals to interact much more easily with each other when it is), so chemists define how much of the solute is in the solution by the term MOLARITY.

Molarity is a really convenient unit of concentration and it works like this. If I have 10 moles of solute in 10 liters of water, what’s the molarity? 10/10 = 1! So it’s a 1M solution. What if I have 20 moles in 10 liters? Then it’s a 2M solution. See how easy that is?

Mole means “heap” or “pile” and is a unit for measuring the amount of a pure substance. It’s a chemist’s dozen. It’s a lot bigger than 12 though. It’s 6.022 x 10^23. So if you had a mole of eggs, you’d have… that huge number at the bottom of the slide. The most confusing part is this…

Elements are arranged so that the ones with similar chemical and physical properties are stacked in vertical groups, and there are 8 groups (see the numbers at the top?) with either an A or B after the number? I know they’re written in Roman… just remember that IV means four, and VI means six. Sometimes you’ll see them numbered 1-18 starting with hydrogen on the left.

The rows are called periods. Now point to the metals… what colors are those? There are lots of them!

Atoms are made of protons, neutrons, and electrons. The protons and the neutrons make up the nucleus (the center) of the atom. The electron lives outside the nucleus in an electron cloud and are way too small to see. Protons and neutrons are made up of smaller little particles, which are made of smaller little particles and so on. Atoms can have anywhere from only one proton and one electron (a hydrogen atom) to over 300 protons, neutrons and electrons in one atom. It is the number of protons that determines the kind of atom an atom is, or in other words, the kind of element that atom is. How many protons does Zinc have?
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Matter that is made of only one kind of atom is an element, like helium. Helium likes to hang out in groups of two helium atoms.

An atom is the smallest particle of an element that still has its chemical properties. If you have a gold atom and you split it into smaller parts (which you can do), it won’t still act like it did chemically as it did when it was a whole atom.
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When doing your experiments, you’ll often repeat an experiment again and again for various reasons. One reason is to make sure the experiment you’re doing is repeatable – it’s not just a one-time thing. You might also be checking to be sure you’ve done it right, or written down the amounts of chemicals correctly, or need to observe something you didn’t previously.

Precision measures how well your answers agree with each other from experiment to the next.

Read the temperature from the thermometer… what do you get? This thermometer is reading in Celsius.

We’ll cover thermometers and the four temperature scales in a bit when we get to thermochemistry, but I just wanted to make sure we’re all on the same page when it comes to reading a thermometer, especially now that so many are digital and some kids may have not yet had the experience of reading a temperature scale.

If you’re going to do a chemistry experiment, you’re going to use chemicals. How much of each one you use is going to change the results you get, so it’s important to find a way to accurately measure out the same amount of chemical each time.

We already talked about how matter is anything that takes up space, like air, kittens, your left armpit… Mass can exist in different states. What are they?

Solid, liquid and gas. You also know about two more additional states: what are they? Plasma and BEC! Can matter exist in more than one state at a time? Sure – ever had a glass of water? That has liquid water and solid water molecules (ice) at the same time!