Chemistry

How can I make slime?

My son and me making slime

Every few months or so, my son and I like to make straight-chain polymers out of of polyvinyl acrylic (PVA) and sodium tetraborate. It’s pretty simple to do. You just mix one part PVA with one part dihydrogen oxide. Then make a solution of about 40 mg of Na2B4O7, and 400 cc of more dihydrogen oxide. Then slowly mix this solution into the PVA mixture. Of course, we add a little food coloring for effect. The result is this great fun-to-play-with polymer!

Okay, so Polyvinyl acrylic is just Elmer’s glue. Sodium Tetraborate is household Borax. And dihydrogen oxide is water. And our polymer is more commonly called slime. I figure it’s never too early to start teaching my son the chemistry behind what we we’re doing. In a nutshell, making your own slime is easy. Here are the steps summarized:

1. Pour a bottle of Elmer’s Glue in a bowl. Add the same amount of water. Stir.
2. Put about the same amount of water in another bowl and add a couple tablespoons of Borax. Stir.
3. Add this Borax solution to the glue mixture a little at a time while stirring.

It doesn’t take much to make a nice slimy polymer. Experiment with the volumes and you’ll see how easy it is.

Do solids behave like gases in-that they can hold more moisture when warm than cold?

Full question, asked by Bob M. I keep a plastic bag of salt on the floor of my garage to melt ice during our Iowa winters. It doesn’t get all used up each season so it just sits there until the next year. This week I’ve noticed a small trail of water on the floor coming from under the bag. It hasn’t rained for 10 days though the year has been exceptionally wet. I assume the salt has absorbed moisture from the air but why is it releasing it now? Do solids behave like gasses in-that they can hold more moisture when warm than cold?

First, let’s do a quick review of why warm air can hold more moisture than cold air. Considering the phase diagram of water (a sample is shown above), at constant pressure, the only variable to determine if it exists as a solid, liquid or gas is Read more…

What is the most abundant element on Earth?

Oxygen is the most abundant. It comprises 49.5% of the total mass of the Earth’s crust, water, and atmosphere. The second most abundant is Silicon (Si) at 27.7% of Earth’s mass. Read more…

What is radioactive half-life?

The half-life of a substance is the time it takes for the number of radioactive nuclei to decrease to one half of the original number. The halflife of a given isotope is always the same, meaning it doesn’t matter how many you have at any given time. Read more…

How do snowflakes form?

Snowflakes are the result of symmetrical crystallization of water molecules as they turn into ice crystals. Water molecules, when pass to crystalline solid state, such as in ice and snow, form weak bonds (called hydrogen bonds) in which two hydrogen atoms tend to attract neighboring water molecules.

When the temperature drops below the freezing point, the water vapor molecules form hydrogen bonds into a solid state, which exhibits the lowest-energy, an open framework that has a basic symmetrical, hexagonal shape of the snowflake. The higher the symmetry, the more stable the crystal, because this maximizes attractive forces and minimizes the repulsive ones.

The crystallization process is like tiling a floor in accordance with a specific pattern: once the pattern is established and the first tiles are put in place, then all the others go in the predetermined pattern to maintain symmetry. Water molecules simply put themselves to fit the spaces and keep symmetry; this way, the different arms of the snowflake appear.

There are many different types of snowflakes (“no two snowflakes are alike”) because a differentiation occurs due to specific forming circumstances: atmospheric conditions, notably temperature and humidity; and in the atmosphere, where conditions are very complex and variable.

A crystal might begin to grow in one manner and then trasformations in temperature or humidity, after minutes or seconds, change the growth pattern. The hexagonal symmetry prevails, but the ice crystal may form a different branching pattern. The atmosphere changes take place over a large area, so the snowflakes in a region are alike.

Source: Softpedia.com.

Why does water boil at a lower temperature at a higher altitude?

In short, a liquid’s boiling temperature is dependent on its composition and the atmospheric pressure on the boundary between the liquid and the air above it. For water, the boiling point at sea level is 100 degrees Celsius (212 degrees Fahrenheit). The atmospheric pressure is roughly 29 mmHg at sea level, but this number is dependent on altitude and is lower the higher you get from sea level.

Boiling is the process in which the molecules in a liquid have enough energy to overcome the opposing pressure of the atmosphere. When these liquid molecules start turning into gas molecules, we say the liquid is boiling. If you lower the opposing pressure, there will be less resistance to the water molecules turning into gas molecules and entering the air, and the liquid will boil at a lower temperature.

It follows that water would boil quicker on a day with lower atmospheric pressure than on a day with a higher pressure. This is true although the difference in barometric pressure on any given day at the same altitude isn’t as great as a change from differing altitudes.