Today’s lab is from the homescientist chemistry kit manual, CK01A, determining the effect of temperature, concentration and surface area on reaction rates.  Its very similar to the lab I did yesterday with the middle school kids, but uses sodium bicarbonate tablets and vinegar. The chemistry kit didn’t come with enough tablets for 4 groups to do this experiment so I bought some off amazon.

Students started with 25ml of chilled (left in fridge over night) vinegar at 13 C and timed how long it took for a sodium bicarbonate tablet to completely react with the vinegar, detemined by the lack of bubbles/fizzing sounds.  They then used room temperature vinegar and repeated the experiment.  To get higher temperatures the beaker with vinegar was placed in the microwave for 5 seconds which raised the temperature about 10 degrees Celsius.  Students found that increasing the temperature reduced the reaction time considerably.

IMG_9153To test the effect of concentration students added 25 ml to their beaker and then added different amounts of water.  They were supposed to do 100%, 50%, 25% and 12.5% vinegar solutions but at least for two groups the 50% was still reacting after 25 minutes!  You can see in the photo above it wasn’t very rigorous but with a flashlight shining on the solution you can definitely tell the reaction was still taking place. This makes sense because even though you have the same number of sodium bicarbonate and vinegar molecules in the beaker, adding more and more water molecules makes it less likely for the vinegar molecules to bump into a sodium bicarbonate molecule… water molecules keep getting in the way.  Since this took so long we skipped the next two and moved on to surface area.

For surface area students dropped in a whole tablet, a tablet cut into four pieces and a crushed tablet.  Increasing the surface area, especially pulverizing the tablet definitely increases the reaction rate (shorter reaction time).

Students graphed reaction times as a function of temperature.  This was a nice straight forward lab and as mentioned before the only thing we didn’t do was the lower concentrations since the reaction times got to long.