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Name: Emily
Status: student
Grade: 4-5
Location: Outside U.S.
Country: USA
Date: Winter 2012-2013


Question:
I am a 5th grader researching for my science project and I have a question about whether acids and/or sugary liquids affect the expandability (volume) of water as it freezes. I need to know the following: 1. If I freeze 10 mL of water in a graduated cylinder what will be its volume when it is frozen? I assume it would rise because of expansion but by how much? 2. If I add acids or sugary liquid to water will it affect the frozen volume, maybe keep it from expanding or minimize its expansion or make it rise higher in the cylinder when frozen compared to just water?



Replies:
1. First, you need to eliminate from your thinking that the volume change has anything fundamental to do with the shape of the container. The volume change upon freezing (or the opposite volume change upon melting) is volume / fraction frozen (or fraction melted). Although you would keep track of those changes, the fundamental change is [fraction increase (or decrease) per fraction frozen (or melted)]. This ratio is a dimensionless.

If the ratio is positive then the volume of the liquid is greater than the volume of the solid as the fraction melted varies from 0 to 1. If the ratio is negative, then the volume of the liquid is less than the volume of the solid as the fraction melted varies from 0 to 1. Whether this volume change is positive or negative depends upon the substance. ?Usually? the volume change upon melting is positive for most substances. Water is a notable exception to this ?rule?. Just how large this change is ?substance dependent? and/or concentration dependent depending upon the solvent and/or solute.

You cannot predict whether this change is going to be positive or negative from first principles. Do not get confused by the shape of the container. It is the VOLUME fraction versus fraction MELTED or (FROZEN). The shape of the container is incidental.

Vince Calder


Hi Emily,

Thanks for the questions. For question 1, I would recommend obtaining a 10 mL graduate cylinder and filling it with 9 mL of water and then freezing it. You can then measure the volume of the frozen water in the cylinder. You will find that the volume increases by 0.1 mL or so. That is not a large amount, but it is noticeable.

For question 2, the answer depends on how much and of what type of acid or sugar you add to water. For instance, if salt is added to water, the water freezes and salt is excluded from the ice. This is the reason why you can eat ice from icebergs and it will not taste salty. Some sugars may actually cause the water to freeze at a lower temperature than 0 degrees C. So, I would recommend testing to see if the volume increases or decreases when water is frozen. I would use the graduated cylinder that you have available and fill it with 9 mL of the liquid and then freeze the liquid.

Since this is a science project, I want you to investigate the questions you have and find out if the volume does increase or decrease. That is the reason why I am not giving you the answers directly.

I hope this helps. Please let me know if you have more questions. Thanks Jeff Grell


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