As you may know, Alka Seltzer is a substance that can soothe an uneasy tummy. Oftentimes if you have eaten too much your stomach can produce too much acid which can make you feel not so good. Alka Seltzer contains sodium bicarbonate which can react with that extra acid to neutralize it – and it may give you the burps as well because the reaction creates carbon dioxide gas which will want to escape from your body. We are going to take a look at this reaction in action and see what else can affect the reaction.
Materials:
- Alka Seltzer tablets (or generic brand antacid tablets)
- Vinegar
- Water
- A film canister
- A knife for scoring tablets
- Watch or clock with a second hand
- Ice
- Heat source (microwave or stove)
Safety Considerations:
EYE PROTECTION IS REQUIRED FOR THIS EXPERIMENT. Expect the lid of the canister to be a projectile and that the vinegar may come out of the canister as well. Protective eyewear is recommended and the use of gloves may also be warranted particularly if there are any open abrasions that the vinegar can interact with. If the canister is tipped upside down this will certainly cause a mess as the liquid will spill all over. Adult supervision is strongly recommended.
Experiment:
We will try multiple experiments where we vary the concentration of the vinegar and then a series of experiments where we vary the temperature. Cut two Alka Seltzer tablets into 8 equal sized tablets. We will do a control to start with by using just water. Take the top of the vinegar container off and fill the cap five times with water, emptying the water each time into the empty film canister. As soon as you drop the ¼ sized tablet into the canister with the water, cap the canister and begin timing how long it takes for the lid to blow off the top. In the second trial, put 1 capful of vinegar and 4 capfuls of water into the canister and repeat the experiment.
After that, try 3 capfuls of vinegar and 2 capfuls of water and in the last experiment, try 5 capfuls of vinegar. These were all done at room temperature so in other experiments, you can try cooling one of your experiments from above (pick one that gave a reasonable time frame) by placing the solution on ice for a while. You can also try heating the solution as well to see how that affects the time it takes for the cap to blow off.
What’s happening?
Sodium bicarbonate, NaHCO3, will react with acid, H+, to create water (H2O), Na+, and CO2 as seen here:
NaHCO3 + H+ –> Na+ + H2O + CO2
The CO2 is a gas and this will build up and create enough pressure to blow the top off of the canister. By increasing the amount of H+ in the canister, it will make the reaction go faster causing the lid to blow off sooner. This is because you are causing more H+ to collide with the baking soda. And, vinegar is a good source of H+. Water does not contain much H+, so Alka Seltzer puts an acid (citric acid) into the tablet so that when it dissolves into the water it can react with the NaHCO3. We also find that the hotter the temperature, the faster the reaction will go as well. This is because you are making the molecules move faster so that more collisions happen in the same period of time causing the reaction to go faster. You could do another experiment and see if a crushed tablet will go even faster! Additionally, if you want a little more excitement, try turning the canister upside down! This will cause the canister to be a rocket instead of the lid. You may want to do this outside though where messes aren’t such a big deal. Remember to use protective eyewear!
References:
- http://biocircuits.ucsd.edu/outreach/?category_name=Experiments&paged=2
- https://www.youtube.com/watch?v=nsayFUSwKfs&feature=youtu.be
To view all past “ChemShorts for Kids”, go to:
http://chicagoacs.org/articles/article_category/1
