How does particle size affect the rate of dissolving? -- An Student Designed Inquiry

 As part of the Culminating Performance Task my grade nine applied science class used the Smarter Science emergent scientist templates (poster set three) to design and conduct an inquiry into the effect of particle size on the rate of dissolving. The solute we dissolved was store bought Alka-Seltzer tablets and the solvent we used was water.

Due to the nature of the learners in my class I assumed that some of them would have no prior knowledge of Alka-Seltzer. So I started the class by showing them the box I had purchased from the drug store, then I opened the box and showed them the packages within and finally I opened the packages and showed them the tablets. Next I showed them Alka-Selters advertisements from Youtube then I dropped one of the tablets into a beaker of water and demonstrated how to time the dissolving process from beginning (initial time) to end (final time). 

While demonstrating the last step I invited the students to pull out their digital devices and use the timers on them to help with the timing. This step allowed the students to become familiar with the timing devices they didn’t even know they had, as well as become aware of the importance of starting and stopping the timer at precisely the right moment in order to record accurate results. Because I had a limited number of tablets available and an even more limited budget with which to purchase more I wanted to ensure that no tablets would be wasted during the actual lab due to failure to record the dissolving time. 

Using the Smarter Science template the students determined that the independent variable for their investigation would be the particle size while the dependent variable would be time (rate). The controlled variables would be:

1.      Size of beaker

2.      Volume of water

3.      Temperature of water

4.      Mass of tablet (predetermined by pharmaceutical company)

5.      Timing device

Each group was given four tablets for their investigations. The particle sizes they would experiment with were:

1.      Whole tablet

2.      Whole tablet broken into halves

3.      Whole tablet broken into quarters

4.      Whole tablet crushed

Each group decided what values to give to their controlled variables and recorded them on the Smarter Science template. Once everything was planned and recorded in an intelligible fashion the students were given their four tablets and got down to some serious science.

This lab worked very well. After performing and recording the investigation the students cleaned up, washed their hands and began analyzing their results. Because most of these students are visual learners I had them use their data to construct a line graph. The results were universal, the crushed tablet dissolved at a much greater rate than any of the other formats. In their written report the students reflected how this knowledge could be used in their daily life. Most have decided to chew their prescribed tablets in the future instead of swallowing them whole. 

 
What labs have your students designed and conducted to investigate the effects of particle size on the rate of dissolving?
Can you recommend any less expensive solutes?