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Hot Hands, Instant Crystals, and Super Cool Solutions
By Elizabeth D, November 7, 2012 at 3:50pm PERMALINK
As the weather gets colder, fingers get frosty. Most chemical hand warmers are single use and take a while to warm up. But it's easy to make an instant, reusable hot pack with two simple ingredients: baking soda and vinegar. Follow the recipe below to make your own at home!
Materials:
Materials:
- 1 cup white vinegar (acetic acid C2O2H4)
- 5 level teaspoons of baking soda (sodium bicarbonate NaHCO3)
OR
- 1 cup and 2 tablespoons white vinegar (acetic acid C2O2H4)
- 3 level teaspoons of washing soda (sodium carbonate Na2CO3)
PLUS
To Do:
Troubleshooting:
A Closer Look
Both baking soda (sodium bicarbonate NaHCO3) and washing soda (sodium carbonate Na2CO3) are bases. Vinegar (acetic acid C2O2H4) is an acid. When either baking soda or washing soda is mixed with vinegar, they react to form liquid water (H2O) carbon dioxide gas (CO2) which is the source of the bubbles, and disolved sodium acetate (NaC2O2H3). Heat helps to speed up this reaction and causes some of the liquid water to turn into steam. As more water evaporates into steam, it leaves behind the sodium acetate.
Eventually there is so much more sodium acetate left behind than water that it begins to turn solid. when you add heat, you're giving energy to the molecules of sodium acetate. The moving molecules can't latch on to each other to make the organized structures that make up crystals. Adding a few grains of sodium acetate powder provides a little organization to the liquid, and the molescules are able to line up to form the crystals.
As the solution crystallizes, the molecules slow down and give off that extra energy as heat. Because sodium acetate is so good at this, it is used in some kinds of commercial instant hand warmers. We use a few on them here in OMSI's Chemistry Lab!
These commercial hand warmers use a metal plate within the enclosed solution. When bent or rubbed the plate will irritate the solution and cause crystallization to occur. Instant warm hands! These can be melted back down to the original solution and used again and again.
- One small, clean glass jar with lid (baby food jars work well, or spice bottles)
- A small resealable plastic bag or another small jar
- Frying pan
- Spoon
- Plastic spatula
To Do:
- Measure the baking soda or washing soda into the frying pan. Add a small amount of vinegar. What happens?
- Stir the solution until the bubbles disappear.
- With an adult's help, warm the pan over medium heat. Continue to stir the solution.
- Repeat steps 2 and 3 until the solution starts to turn into a white powder around the edges and there is less than 2 tablespoons of solution left in the pan. This is now a super saturated solution!
- Carefully pour this solution into the jar. Caution! The solution is very hot! Set it aside until it is at room temperature and then put the lid on the jar until you are ready to use it.
- Do not wash the frying pan yet! Allow it to cool completely and wait for all the liquid to evaporate. What is left in the pan?
- Using a plastic spatula, scrape off the white powder (this is sodium acetate) and store it in a resealable plastic bag or another small jar. Label it "sodium acetate powder". This powder will be used as seed crystals.
- Once the liquid in the jar is at room temperature, feel the bottom of the jar. Is it hot or cool?
- Use a spoon to scoop up only a few grains of the sodium acetate powder. Open the jar and drop them in. What do you see?
- Feel the bottom of the jar. What do you notice?
- To reset the sodium acetate solution, pour water into a pan about 1 inch deep. Heat the water over medium-high heat. Once the water is hot (but not boiling) set the jar in the water. The now solid sodium acetate will melt. Once it has melted completely, remove the jar from the hot water bath and set it aside to cool. When it it completely cool, replace the cap until you're ready to use it again!
- Wash the pan, spoon, and spatula thoroughly.
Troubleshooting:
- If the super saturated solution does not make crystals immediately or at all, or slowly grows long, thin crystals in the solution after you add the seed crystal, then there is too much water in the solution. You can either leave the container in a sunny place with the lid off to allow some to evaporate, or heat the jar in the water bath for an extended amount of time to get rid of excess water.
- If the solid solution won't melt completely or it forms crystals when it cools after melting, there isn't enough water in the solution. Add a few drops of water to the jar and repeat the melting process.
- If you run out of seed crystals, put a drop or two of solution onto a smooth surface (like a plate, tile or jar lid) and wait for the water to evaporate and leave behind white crystals.
- This solution can be used over and over again!
A Closer Look
Both baking soda (sodium bicarbonate NaHCO3) and washing soda (sodium carbonate Na2CO3) are bases. Vinegar (acetic acid C2O2H4) is an acid. When either baking soda or washing soda is mixed with vinegar, they react to form liquid water (H2O) carbon dioxide gas (CO2) which is the source of the bubbles, and disolved sodium acetate (NaC2O2H3). Heat helps to speed up this reaction and causes some of the liquid water to turn into steam. As more water evaporates into steam, it leaves behind the sodium acetate.
Eventually there is so much more sodium acetate left behind than water that it begins to turn solid. when you add heat, you're giving energy to the molecules of sodium acetate. The moving molecules can't latch on to each other to make the organized structures that make up crystals. Adding a few grains of sodium acetate powder provides a little organization to the liquid, and the molescules are able to line up to form the crystals.
As the solution crystallizes, the molecules slow down and give off that extra energy as heat. Because sodium acetate is so good at this, it is used in some kinds of commercial instant hand warmers. We use a few on them here in OMSI's Chemistry Lab!
These commercial hand warmers use a metal plate within the enclosed solution. When bent or rubbed the plate will irritate the solution and cause crystallization to occur. Instant warm hands! These can be melted back down to the original solution and used again and again.