Giant Soap Bubbles

Physics, Chemistry:	Surface Tension, Bubble Formation
Grade Range:	Elementary School, High School
Format:	Hands-on, Stage

Our giant soap bubble solution can make some impressively big bubbles. Elementary school students will love playing with the bubbles, and high school students will be fascinated by the science! This demonstration gets messy pretty quickly, so either perform this demonstration outdoors or bring a large tarp to catch the mess.

Materials

• Big Bubble Solution:
  • Water
  • Glycerin
  • Liquid Dish Soap
• Big Bubble Wands
• Large Bowls or Tubs

Safety Precautions

Please read the Liquid Chemical section of the Demonstration Safety page before performing this demonstration.

Demonstration

Preparation: Making the Big Bubble Solution

1. In a large container, mix two cups of soap with six cups of water. Mix it slowly to minimize the suds formed.
2. Clear away most of the suds from the surface, and add 1/3 cup of glycerin, stirring while adding it in slowly. Once fully dissolved, store the solution in a container and label it. The solution will last about a year, but should be mixed prior to every use.

Presentaiton

1. Pour the bubble solution into several large bowls or tubs. Set the big bubble wands next to the tubs. If indoors, lay out a tarp in front of the table the tubs are on to help catch any mess.
2. Let students come up and have fun! the solution can make bubbles that are several feet wide, and students will love playing with it.

Why This Works

Short Explanation

Surface Tension is the attraction between the liquid molecules, and is what holds the liquid together. Water we know has surface tension, and because of the surface tension of water it will try to be a ball or sphere. Bubbles are what happens when you are really stretching the surface tension, and the molecules try to stay connected even as we make the bubble bigger. We know that adding liquid soap can make bigger bubbles, and this is because soap is really good at spreading out and staying stuck together. However, to make really big bubbles we need a secret ingredient: glycerin, or sugar! When sugar is dissolved in water, it helps to pull the water molecules towards each other, acting like a grid for the water molecules to spread out evenly across. This, combined with the soap, can make some very large and very impressive bubbles!

Full Explanation

Surface Tension is the attraction between liquid molecules at the surface caused by the bulk of the liquid. Surface tension results in minimal surface area, which is why water droplets are always spherical. Surface tension is also why a liquid will sometimes form bubbles on the surface. When a bubble forms, it has the liquid spread out thinly around a pocket of air. The liquid's surface tension is holding it together, but it is deteriorating due to evaporation, which happens much faster due to the liquid's surface being spread so thinly. This is why soap bubbles break down on their own fairly quickly; although the soap works to help spread the water further, and therefore to get a bigger bubble, the water is still evaporating.

For the giant bubble solution, we added in glycerin. Glycerin helps the bubble last longer and to grow bigger by doing two things; decreasing the surface tension and resisting evaporation. Glycerin and soap are Surfacants, or compounds that help to decrease the surface tension of a liquid. The soap decreases the surface tension of the water, but it doesn't do much to decrease the rate of evaporation. This is why soap bubbles tend to pop pretty quickly after you make them, unless they stay on the surface of the solution. Glycerin, however, helps to reduce the rate of evaporation. When you dissolve sugar in water, the sugar molecules spread out and try to stay evenly distributed. When you make a bubble with the sugar solution, the sugar molecules in the bubble start losing some water due to evaporation. However, hydrated sugar molecules have strong attractions to each other, so they will start linking together and making a "grid" across the bubble's outer surface. This grid locks in the water molecules, and makes it harder for the water to evaporate. The additional soap in the solution helps to spread the water out as you make the bubble bigger. Combined, the soap and glycerin work together to prevent additional evaporation and lower surface tension, resulting in giant bubbles!

Additional Information

• This demonstration pairs well with the Floating Soap Bubbles and the Glowing Bubbles.