Why does your voice sound weird when you breathe helium gas?

Answered by Alan Jensen, Registered Pharmacist

That is a very interesting question. Sound travels at different speeds in different mediums. In a gaseous medium sound travels faster in lighter gases, and the faster the sound travels, the greater the frequency or higher the pitch of the sound. Since helium is about seven times lighter than air, sound travels about two times faster in helium than in air.  When you breathe helium, sound travels faster in your throat and mouth making the pitch higher so you sound like Donald Duck. Conversely, breathing argon (a heavy gas) makes a lower pitch sound or Goofy voice. 
As a Pharmacist, I am concerned about the safety of breathing helium.  Helium is chemically inert and will not harm you.  However, helium will displace oxygen in your lungs eventually depriving your brain of oxygen, which may make you faint.  I have heard of people breathing helium from the tank instead of a balloon. The pressure of the tank could cause the tiny air sacks in the lungs to rupture causing severe problems.  Lastly, helium used to blow up balloons could be contaminated with other chemicals that could be harmful.  All in all breathing helium is not a good idea.

Density and Buoyancy
Every object on earth is made of atoms. Gravity pulls these atoms to the earth. You can measure the pull of gravity on an object. We call that measurement weight.

A molecule is a group of atoms bonded together. Density is how close together the molecules of a substance are or how much mass a substance has in a given space.

For example, if you have one cup of jelly beans and one cup of marshmallows, the jelly beans have more mass because there is more “stuff” compacted into the cup. The marshmallows have less mass because the molecules of marshmallows are NOT close together. Marshmallows are mostly air.

Materials with more density weigh more. A cup of jelly beans weighs more than a cup of marshmallows.

For an object to be buoyant, or float, it must have less density that what it is floating in.
Helium is called a “lighter than air” gas, because it is less dense than air.  Because helium has less weight that the air it is floating in, the helium balloon floats!

Make a Ketchup Packet Float
Materials:  1-liter plastic bottle, ketchup packet from a fast food restaurant, salt

  1. Remove any labels from the bottle and fill it all the way to the top with water.
  2. Add a ketchup packet to the bottle.
  3. If the ketchup floats, you’re all set – go to step 4. If the ketchup sinks, go to step 5.
  4. If your packet floats, screw the cap on the bottle and squeeze the sides of the bottle hard. If the ketchup sinks when you squeeze it and floats when you release it, congratulations, you’re ready to show it off. If it does not sink when you squeeze it, try a different kind of ketchup packet.
  5. If the ketchup packet sinks, add about 3 tablespoons of salt to the bottle. Cap it and shake it up until the salt dissolves. Continue adding salt, a few tablespoons at a time until the ketchup is just barely floating to the top of the bottle. Once it is consistently floating, make sure the bottle is filled to the top with water, and then cap it tightly.
  6. Now squeeze the bottle. The magic ketchup should sink when you squeeze the bottle and float up when you release it. With some practice you can get it to stop in the middle of the bottle.


This experiment is all about buoyancy and density. There is a little bubble of air inside of the ketchup packet. Bubbles float, and the bubble in the ketchup sometimes keeps the heavy packet from sinking. When you squeeze the bottle hard enough, you put pressure on the packet. That causes the bubble to get smaller and the entire packet to become MORE DENSE than the water around it and the packet sinks. When you release the pressure, the bubble expands, making the packet LESS DENSE (and more buoyant) and it floats back up.

If you had to add salt to the water, you adjusted the water’s density to get the ketchup to float.

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