Re: Does baking soda lower the temperature of hot water?

Hi Ozzie, 

Your question could mean two different things:  

1. Baking soda could lower the temperature of hot water when you add it, if 
the baking soda were colder than the water and you added enough of it.  
This is like adding an ice cube to soup when you want to cool the soup.  
The ice cube melts and the soup gets colder, because the two things tend to 
become the same temperature.  Likewise, if the baking soda were warmer than 
your water, your water might get warmer after you added baking soda.  

2. If you mean, "Does adding baking soda change the freezing and boiling 
temperatures of water?" then there is a different explanation.  When you 
add salt to water and then boil the water, you increase the boiling point 
of the water.  Water normally boils at 100 degrees Celcius, but if you add 
enough salt to it, it will boil at a slightly higher temperature.  It will 
also mean that salted water freezes at a lower temperature than pure water.  
(This is also how antifreeze works.)  Baking soda will have the same effect 
as table salt, though to a slightly smaller degree.  If you add enough 
baking soda to your water, then boil it and take the temperature, you'll 
find that the temperature is higher than 100 degrees celcius.  

Why adding salt or baking soda to water results in an increase in the 
boiling temperature (or decrease in the freezing temperature) has to do 
with the salt and baking soda disrupting the normal pattern of water 
molecules in pure water.  When you boil water, the bonds between water 
molecules break and the water turns into steam.  If you add salt, the water 
no longer bonds to just water, but to salt as well.  Water will stay with 
the salt rather than turn into steam at 100 degrees, so you need to add 
more heat to get water to boil. 

By the way, all of this information is accurate as long as you live at sea 
level.  I live in Boulder, Colorado where the elevation is about 1 mile 
high.  If I did this experiment, the boiling salted water would be LOWER 
than 100 degrees Celcius.  The pressure is lower up here, and the boiling 
temperature of water is also lower.  You don't have to worry about this in 
New Jersey.

I hope that this explains your results.  You might want to see how varying 
the amount of baking soda you add to water effects the temperatures.  Good 
luck with your project.

Sarah Earley
CU Boulder