Kids are natural chemists. They love to mix things together and see what happens. My kids call it making potions.

They would pull every powder and liquid they could find out of the pantry, pour a little bit of everything into a bowl and mix it up. Inevitably, some acid (lemon juice or vinegar) and a base (baking soda or powder) were added to the mix and much to their delight bubbles followed.

But one thing they didn’t notice was that sometimes the solutions get cold and sometimes they get hot.

Instead of sticking a hand into the gooey potion in the bowl to observe a change in temperature, mix the potions in a resealable plastic bag.

Try out these simple combinations of a salt* and a liquid in a Ziploc bag. Just add 1-2 tablespoons of each ingredient. Hold the bag in your hands to feel if the reaction releases heat, called exothermic, or absorbs heat, called endothermic.

**Safety First!  Be careful not to spill, drink, eat or inhale any of the chemicals. Do not seal the plastic bags as they can explode if the reaction produces a gas.

  • Magnesium sulfate (aka Epsom salt) + water
  • Calcium carbonate (aka Ice Melt salt) + water
  • Sodium Bicarbonate (aka baking soda) + water
  • Sodium Carbonate (aka washing soda) + water
  • Magnesium sulfate (aka Epsom salt) + vinegar
  • Calcium carbonate (aka Ice Melt salt) + vinegar
  • Sodium Bicarbonate (aka baking soda) + vinegar
  • Sodium Carbonate (aka washing soda) + vinegar

Also try these…

  • Steel wool + vinegar
  • Citric acid (or lemon juice) + Sodium Bicarbonate (aka baking soda) + water (if not using lemon juice)
  • Calcium chloride (aka Ice Melt salt) + steel wool + water
  • Hydrogen peroxide + yeast

*All the “white powder” ingredients (even baking soda and washing soda) are salts!

Some of these reactions produce a gas and some produce a precipitate, or solid.

Some of these reactions aren’t actually reactions but just a salt dissolving in water. When a salt dissolves sometimes it breaks down into its pieces.   For example when table salt, sodium chloride, dissolves in water, the sodium separates from the chloride and they float around in the water. Sometimes energy is absorbed to break up the salt making the bag feel cold. This is an endothermic process. Other times, energy is released and the bag feels warm. This is an exothermic process.

Make it a Science Experiment
You can turn this investigation into an experiment by adding a thermometer to the mix. Which combination gets the hottest and which gets the coldest? Does it matter how much of each ingredient you add to the bag?  Are reactions that produce a gas always exothermic or endothermic?  What about reactions the produce a precipitate?

Make it an Engineering Challenge
Use what you’ve learned about the endothermic and exothermic reactions above to design a hand warmer or a cold pack (or both!). How can you make sure the chemicals don’t mix until you are ready? If the reaction produces a gas, how will you make sure it doesn’t explode? Test your design – how hot or cold does the pack get and how long does it last?

Hot and Cold Chemistry
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