Science Buddies: "Ask an Expert"

Posted on behalf of parent/student

Project: https://www.sciencebuddies.org/science- ... ction-rate
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I was hoping someone could reach out to help us with our son's 6th grade Science Experiment. We ordered the Home Science kit that is suggested with the science experiment called: "Can you Change the Rate of a Chemical Reaction by Changing the Particle Size of the Reactants?"

We followed the instructions closely and we even tested the tube apparatus when, after the first trial with a full tablet of Alka Seltzer, we could not detect any changes in the graduated cylinder. We tested the apparatus by blowing air into the tube that would have been coming from the bottle with the alka seltzer and water and could clearly see plenty of bubbles when we did that but on the actual whole tablet trials, we timed it up to beyond 3 minutes and did not see a clear change in the graduated cylinder. Since we are testing particle size and not temperature, we kept the temperature at room temperature noting it as 72 degrees. There did not seem to be any kinks in the tubing, the tube is feeding under and into the graduated cylinder placed upside down in a bucket of water and the graduated cylinder is full of water. We used the 250 ml graduated cylinder as recommended in the instructions and used 120 ml of water in the squeeze bottles. We tried first with a whole tablet of Alka seltzer and then a 2nd tablet but on the second test trial we tried the crushed or powdered tablet to see if we could get any kind of reading in the graduated cylinder and we still did not.


[[After reviewing the setup and testing of the setup by blowing directions]]

I did "test' the tubing by blowing into it and saw the bubbles go to the graduated cylinder no problem.

When we researched a bit about how much CO2 is generated from an Alka Seltzer tablet, it was just a few grams which corresponded to about 7 ml in volume: at least that's what my husband saw in his online research.....so I am wondering if the amount of volume change is so small, maybe we could not detect it in a 250 ml cylinder: do you think we should try using the 100 ml cylinder?

Our set up looked just like the one in the picture in the instructions. One question I have though is how far should the tubing go up into the graduated cylinder that is completely filled with water. Are we going to see air bubbles that will push the water volume down in the graduated cylinder??


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Subsequent outline of situation:
We put 120 ml (recommended amount) of room temperature water (took the temp of it as 72 degrees) in the squeeze bottle.

We also assembled the 250 ml cylinder: We filled it with water the 2nd recommended way (putting plastic over it and then transferring to the tub and remove the plastic: We did it this way as our tub was not big enough to put the cylinder completely under water and fill it that way.

I have included two photos showing the tub with the graduated cylinder taped with clear packaging tape (the paper clips are there for more reinforcement to keep the tape from coming off the edge of the tub). The 2nd close up photo is to show that the tubing is going up into the graduated cylinder: it is not really explained in the experiment instructions how far that tube should go but I didn't want it slipping out the bottom. If we should be placing the tubing higher up the cylinder please let me know.

We did blow into the tubing to test it and clearly saw bubbles in the cylinder so we refilled the cylinder to do the first trial. In the plastic squeeze bottle we are seeing bubbling and when we tried again with a powdered tablet we did see a couple bubbles occur but the volume change was very small.

If all of this is correct, three things might help us:

1) Can you give a relative guideline of how much or a range of volume change we should see or expect

2) Another idea I had is, if the volume change will be small, could we use the 100 ml graduated cylinder and perhaps we can see the volume change better as it is narrower. The directions say to use the 250 ml cylinder but honestly, it is hard to see any change.

3) Should we use extra strength Alka Seltzer tablets throughout the trials: maybe the higher concentration will cause more bubbling??

Reply from a scientist at Science Buddies:

Your questions are repeated here with some answers and troubleshooting help:

1) Can you give a relative guideline of how much or a range of volume change we should see or expect?

Reply: There should be a significant amount of gas created from the Alka-Seltzer tablets, approximately 17mL per tablet at normal standard pressure and temperature. The chemicals in these tablets can degrade over time. I would double-check that they have not expired, and potentially repeat the experiment with a new batch of tablets.

2) Another idea I had is, if the volume change will be small, could we use the 100 ml graduated cylinder and perhaps we can see the volume change better as it is narrower. The directions say to use the 250 ml cylinder but honestly, it is hard to see any change.

Reply: You could definitely try this, but it sounds like there may be something wrong with your Alka-Seltzer tablets or potentially part of the setup. From the images, it looks like the plastic wrap may still be on the apparatus; make sure this is removed before re-testing your setup.

If you have already done this, make sure gas is not escaping from another part of the apparatus. Ensure the tubing is far enough up the inverted graduated cylinder (a few inches is great) so that the gas can't escape out of the bottom of the cylinder during carbon dioxide gas production.

Note that after testing by blowing into the tube, which you did successfully, you do have to refill the cylinder: Step 2.d under Figure 3: "(You will need to reconnect the tube to the bottle and re-fill the cylinder before starting your experiment.)"

3) Should we use extra strength Alka Seltzer tablets throughout the trials: maybe the higher concentration will cause more bubbling?

Reply: Extra-strength tablets could be used, and should yield more gas production!

One additional suggestion that may help is to add a bit of food coloring to the water so that you can more easily see the water level and confirm the cylinder is filled properly.

We hope this information helps. Your student should be overserving clear differences with the different formats of the Alka-Seltzer tablet being used.

If you continue to have trouble, you might use your phone and take a short video, if possible, showing what happens when a tablet is added. (Again, this will be easier to see if you add a drop of food coloring.)

Amy
Science Buddies