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Lesson #11: Precision & Accuracy

Lesson #12: Sig Figs

Lesson #13: Atoms

Lesson #14: Zinc Dust

Who gets to burn something today? YOU get to burn something today!

You will be working with Zinc (Zn). Other labs in this kit allow us to burn metal, but there is a bit of a twist this time. We will be burning a powder.

Why a powder instead of a solid ribbon or foil as in the other labs? Have you heard of surface area being a factor in a chemical reaction? The more surface area there is to burn, the more dramatic the chemical change. So, with this fact in mind, a powder should burn faster or be more likely to burn than a large solid.

Zinc (Zn) is a metallic element. It is element #30 on the periodic table. Chemically, it is similar to magnesium, another element that we use in our experiments.

Brass is an alloy of zinc and copper. Brass has been an important metal since the 10^th century B.C. Alchemists in the dark ages burned zinc in air, just like we will do, to make what they called “white snow”. Their “white snow is our zinc oxide.

Zinc is an important element in our lives. Zinc deficiency causes lack of proper growth, delayed physical maturation, and susceptibility to infection. Zinc deficiency contributes to the death of 800,000 children per year. Excess zinc in our bodies can cause problems for us as well.

Materials:

Alcohol burner
Lighter
Measuring spoon
Zinc powder (MSDS)
Porcelain tile work surface

Remember to dispose of your zinc oxide in the outside trash, and conduct your experiment in a well ventilated area. Fumes from this experiment are irritating and a little dangerous.

Download Student Worksheet & Exercises

Here’s what’s going on in this experiment:

Zinc powder will burn in the presence of oxygen, producing interesting colors. The flame from burning zinc is blue, as the zinc undergoes a chemical change to become zinc oxide. Zinc oxide is thermochromic. That means that it changes colors depending on the temperature. When cool, ZnO is white. When heated, zinc oxide turns yellow, and as it cools, returns to become a white powder again. The color changes are caused by a small loss of oxygen at high temperatures, and a small gain of oxygen as it cools in air.

2Zn + O₂ –> 2ZnO

Zinc powder burned in air reacts with the oxygen and turns into zinc oxide. Zinc oxide is used in sunscreen and to treat burns, cuts, and diaper rash.

Cleanup: Clean everything thoroughly after you are finished with the lab. After cleaning with soap and water, rinse thoroughly. Chemists use the rule of “three” in cleaning tools. After washing, chemists rinse out all visible soap and then rinse three times more.

Storage: Place all chemicals and cleaned tools, and glassware in their respective storage places.

Disposal: Dispose of all solid waste in the garbage.

Lesson #15: Periodic Table

Lesson #16: Alkali Metals

Lesson #17: Turning Coppuer into Gold

No kidding! You’ll be able to show your friends this super-cool magic show chemistry trick with very little fuss (once you get the hang of it). Before we start, here are a few notes about the setup to keep you safe and your nasal passages intact:

The chemicals required for this experiment are toxic! This is not an experiment to do with little kids or pets around, and you want to do the entire experiment outside or next to an open window for good ventilation, as the fumes from the sodium hydroxide/zinc solution should not be inhaled.

This experiment is not dangerous when you follow the steps I’ve outlined carefully. I’ll take you step by step and show you how to handle the chemicals, mix them properly, and dispose of the waste when you’re done.

Goggles and gloves are a MUST for this experiment, as the sodium hydroxide (in both liquid and solid form) is caustic and corrosive and will burn your skin on contact.

Is it REAL gold?

No. But it’s very close in color, as is the ‘silver’. The basic idea behind the experiment is this: by cleaning the pennies in the first step, you clear off any oxide layers to expose the copper surface. When you dip it in the solution, a galvanization reaction starts (just like ‘galvanized nails’) covering the penny with a metallic silver zinc coating.

The torching process fuses the zinc and the copper together to make the gold colored brass coating. Be careful, though, as brass has a low melting temperature and if you leave it in the flame too long, you’ll burn off the brass coating.

Materials:

propane torch with adult help
shiny copper pennies
distilled white vinegar
Pyrex glass beaker
sodium hydroxide (solid)
zinc powder (dust)
alcohol burner
stand that fits over the alcohol burner
lighter with adult help
wire mesh screen
popsicle sticks
water
salt
disposable cup
gloves
goggles
tweezers or pliers

Download Student Worksheet & Exercises

The chemical reaction plates the copper on the penny with zinc (called galvanization). The zinc reacts with the hot sodium hydroxide solution to form soluble sodium zincate (Na₂ZnO₂), which is converted to metallic zinc when it hits the surface of the penny.

Heating the penny fuses the zinc and copper together to form an alloy called brass. The amounts of copper and zinc in brass can vary a lot, from 60-82% copper and 18-40% zinc.

DISPOSAL INSTRUCTIONS: If you simply wipe out the beaker with a paper towel and toss it in the trash, you run the risk of igniting your trash can because the combination of sodium hydroxide and zinc is very exothermic (lots of heat is generated).

Make sure to use plenty of water to remove the sodium hydroxide first before removing the metal. Sodium hydroxide will not harm the plumbing in the sink as it is also used as a drain cleaner (dissolves hair, etc.) but don’t get it on your hands! Vinegar will neutralize any residual sodium hydroxide.

Lesson #18: Moles & Grams

Lesson #19: Air has mass (hidden CO2)

If you’ve ever burped, you know that it’s a lot easier to do after chugging an entire soda. Now why is that?

Soda is loaded with gas bubbles — carbon dioxide (CO₂), to be specific. And at standard temperature (68^oF) and pressure (14.7 psi), carbon dioxide is a gas. However, if you burped in Antarctica in the wintertime, it would begin to freeze as soon as it left your lips. The freezing temperature of CO2 is -109^oF, and Antarctic winters can get down to -140^oF. You’ve actually seen this before, as dry ice (frozen burps!).

Carbon dioxide has no liquid state at low pressures (75 psi or lower), so it goes directly from a block of dry ice to a smoky gas (called sublimation). It’s also acidic and will turn cabbage juice indicator from blue to pink. CO₂ is colorless and odorless, just like water, but it can make your mouth taste sour and cause your nose to feel as if it’s swarming with wasps if you breathe in too much of it (though we won’t get anywhere near that concentration with our experiments).

The triple point of CO₂ (the point at which CO₂ would be a solid, a liquid, and a gas all at the same time) is around five times the pressure of the atmosphere (75 psi) and around -70^oF. (What would happen if you burped then?)

What sound does a fresh bottle of soda make when you first crack it open? PSSST! What is that sound? It’s the CO₂ (carbon dioxide) bubbles escaping. What is the gas you exhale with every breath? Carbon dioxide. Hmmm … it seems as if your soda is already pre-burped. Interesting.

We’ll actually be doing a few different experiments, but they all center around producing burps (carbon dioxide gas). The first experiment is more detective work in finding out where the CO₂ is hiding. With the materials we’ve listed (chalk, tile, limestone, marble, washing soda, baking soda, vinegar, lemon juice, etc. …) and a muffin tin, you can mix these together and find the bubbles that form, which are CO₂. (Not all will produce a reaction.) You can also try flour, baking powder, powdered sugar, and cornstarch in place of the baking soda. Try these substitutes for the vinegar: water, lemon juice, orange juice, and oil.

Materials:

baking soda
chalk
distilled white vinegar
washing soda
disposable cups and popsicle sticks

Download Student Worksheet & Exercises

The next video (below) is a BONUS video for you – can you find the items around your house so you can make your own scale? (If you generate a lot of CO₂, you can simply use paper grocery bags suspended on both ends of a broom handle (disconnect the broom part first). Suspend the center of the broom handle from a length of string for pin-point accuracy.

The second part of this experiment (video below) compares the weight of air with the weight of carbon dioxide. Make sure your balance is free to move easily when the lightest touch (your breath) is applied to one of the scales. You can use grocery bags attached to the ends of a broom handle for a larger scale, or modify tiny cups with string and pencils (as shown in the video). Either one works, but you’ll want to be sure the bubbles are (mostly) popped before you pour. And pour carefully or you’ll slosh out the invisible CO₂ gas.

You can create the CO₂ gas in a variety of ways (the image at right shows dry ice submerged in water), including the standard vinegar and baking powder method. Here is another option: Open a 2-liter bottle of soda and quickly pour it into a big pitcher so that it foams up to the top of the container. Carefully pour the gas from the pitcher into the balance. What happens?

Fire extinguisher variation: You can create a fire extinguisher by “pouring” the CO₂ gas onto a lit candle to snuff it out.

Materials:

baking soda
distilled white vinegar
two disposable cups
large container
two water bottles or stacks of books
two long pencils or skewers
string

Lesson #20: Balancing Equations

Lesson #21: Balancing Chemical Equations

Chemistry is all about studying chemical reactions and the combinations of elements and molecules that combine to give new stuff. Chemical reactions can be written down as a balanced equation that shows how much of each molecule and compound are needed for that particular reaction. Here’s how you do it:

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