Have you ever had an injury on the sporting field, while traveling, camping or at work and needed a cold pack? It can be troublesome keeping ice cold while you play out on a sporting field somewhere, and the odds of you carrying a ice pack in your briefcase or purse "just in case" is not all that sensible.
Chemical cold packs that you can buy in drug stores and hunting / fishing supply stores create their own ‘cold’ when you need them. There are a few different types, but they all involve endothermic reactions or processes of some sort. The bags usually contain two different chemicals in different compartments. Breaking a seal allows them to mix, which absorbs heat from the surroundings. These are great for traveling and keeping on hand for "just in case". Putting them on your injury as soon as possible means the reaction will steal its warmth as well, which can reduce swelling and give your body time to deal with the trauma. The problem with these "cold packs" are twofold! First they are fun to play with, especially for kids (age does not matter - lol) and second they can become quite costly at about 1.00 each to keep replacing. The good news is you can make them at home, it is easier than you think AND for a fraction of the cost :)
Homemade Instant cold packs
|Homemade Instant Cold Packs! Just add water to activate.|
You will need
- Sodium bicarbonate (baking soda)
- Citric acid
- Zip-lock plastic bag
- Bottled Water (not pictured)
What to do
- Open the zip-lock bag and pour in three to four teaspoons of citric acid.
- Add the same amount of sodium bicarbonate and mix the powders together.
- Touch the outside of the bag. How does it feel? Is it warm or cold?
- Add a small amount of water to the bag – enough to wet the powder sufficiently. Watch what happens.
- Touch the outside of the bag again. Now how does it feel?
So now that you have had your "Science experiment" for the day, lets make some to keep for later. You use the same principles as above EXCEPT you do NOT add the water. Since water is easily available and most of us carry it in our cars or purses, we have in our offices or can find it when we are traveling (gas stations, restaurants and stores) this is not a big deal!
Add 4 Tsp each of the Baking soda and the Citric Acid to each baggie. Zip up and shake around to mix well. Make sure to remove the air and seal it good, especially for those of us who live in humid climates.
That is it! You are done. Now next time you find yourself with a pulled muscle or twisted ankle you can get some cold relief on it no matter where you are at until you can get to the Dr. to have it checked out!
So what makes this work?? According to science by email http://www.csiro.au/helix/sciencemail/activities/chillingrecipe.html
Sodium bicarbonate is what we call a ‘base’. That means when it is mixed in water, it dissolves to make a solution that has a pH over 7. What does that mean? It means that the chemicals in it love to steal hydrogen ions!
Citric acid, on the other hand, is a little different. Mixed with water, it has a pH under 7, which is technically why we call it an ‘acid’. More importantly, it loves to give hydrogen ions away.
As a powdered solid, the two chemicals can’t do very much. They need to dissolve in water to be able to spread out and react with each other. When they do, they swap some of their atoms. Citric acid gives its hydrogen away, which is used by sodium bicarbonate. We can keep track of this swap-around if we use a chemical equation:
citric acid + sodium bicarbonate –> carbon dioxide + water + sodium citrate
H3C6H5O7 + NaHCO3 –> CO2 + H2O + NaC6H5O7
The bubbles you see are the gas carbon dioxide forming. But why does it feel cold?
Chemical reactions need energy to occur. Sometimes, they then produce more energy than they use and release it into the environment. However in this case, the reaction takes the energy it needs from its surroundings, sucking heat away and locking it away as chemical bonds. This is an ‘endothermic’ reaction, which means ‘heat goes in’, so it feels cold to the touch (it is taking the heat away from your fingers).