Physical Chemistry Laboratory
Introduction to Research – Measuring the Growth Rate of Tendrils in a “Chemical Garden”
Download the following paper: J.H.E. Cartwright, B. Escribano, and C.I. Sainz-Díaz, 2011, Chemical-Garden Formation, Morphology, and Composition. I. Effect of the Nature of the Cations, Langmuir, 27, 3286–3293 as an introduction. When you put crystals of some metal salts you get the formation and growth of “tendrils”, Figure 1.
Figure 1. A metallic silicate tendril growing from a crystal in a sodium silicate solution.
The goal of this laboratory is to give you the opportunity to think like researcher scientists. Today’s problem is to how to measure the growth rate of the tendrils under a couple of conditions. Each group may attack this problem in any reasonable way. Creativity is encouraged.
You will be given a copper salt and an unknown crystal. You may place these in two test tubes or beaker and add a solution of sodium silicate (please conserve the sodium silicate because we have only a limited amount). You will want to record the time you add the solution. Tendrils should form almost immediately.
You can define the growth rate of the tendrils in at least two ways: 1) the millimeters the length increases per second and 2) the increase in mass of a tendrils per second. In both cases you will need the start time when you added the solution. You may try to use a ruler to measure the growth rate as in the first definition. You may weigh a tendril after it has grown and divide by the total time to get the mass increase per second as for definition 2. Are there other definitions of growth rate? Can pictures or movies taken with your smart phones/tablets/computers useful? Be creative and think before you do the experiments. You have two laboratory periods to work on these experiments.
You will report your results in the standard laboratory report format. In the introduction discuss what you find on the chemistry of the formation of the chemical gardens. You have one paper already but please search for more. Present your procedure in the Experimental section. This is what you decide to do in the laboratory – don’t copy this write-up! Present your results and discussion/conclusions as usual.
GOOD LUCK with this Research Project!