I have joined with students at the University of Queensland enrolled in Introduction to Role of Science and Technology Education in Society, (EDUC1706), in an effort to grow sugar crystals over two weeks. I was supposed to start earlier but things in life got busy which sent me running around the city getting things organised.
So tonight I went about preparing the experiment. The aim of the experiment is to study the effect of temperature variations on crystal growth. Students of EDUC1706 could pick from placing a saturated sugar solution with a Lifesaver lolly, (a hard sugar candy that looks like a life preserve device, hence the name), in one of four locations:
- A cold location (a fridge)
- Location with large temperature fluctuations (outside)
- Location with small fluctuations (inside)
- Consistently warm location (well heated room with a constant temperature)
I have decided to test a solution in each type of location. It’s growing sugar crystals and after hours of organic chemistry labs and experienced the trials and tribulations of recrystallisation, I am not expecting this to be too difficult when the instruction is then to monitor the solution daily for two weeks as water evaporates.
Figure 1: Sugar solutions and lifesaver lollies
Once the sugar solution cooled, I placed the lifesavers into the sugar solution and saw something quite alarming. The lifesavers were dissolving! My sugar solution didn’t have enough sugar dissolved in it to inhibit the lifesavers dissolving. I started my sugar solution all over again. This time, I had 300mL of water and just poured in the sugar into a saucepan of hot water constantly stirring. I reached a point where the sugar just wasn’t dissolving and with the fear of dissolving another batch of lifesavers, I kept the heat on all the while stirring.
By this point the sugar solution was quite thick, almost like a creamy soup. And then the solution boiled and the remaining sugar crystals dissolved. I added the last of the sugar that I had in the container and stirred until dissolved. I removed the solution from the heat and found that sugar was recrystallising on the surface. I had created a sugar solution that was saturated at a much higher temperature than room temperature. I placed the saucepan back on the heat and filled my four glass jars with the sugar solution and left them to cool.
In physical chemistry, saturation is when the solution of a substance, (in this case sugar), can no longer dissolve more of that substance. The thing is with saturation is that it is dependent on temperature and the chemical properties of the substances involved in creating a solution. In this particular experiment, temperature is the variable that is key. In this case, the hot solvent, (water), is able to dissolve more sugar than at a cooler temperature. As the temperature decreases, the solubility of sugar decreases and as the solution cools, two things can happen. Excess solute, (sugar), precipitates and forms sugar crystals or no solute precipitates. When no solute has precipitated the solution now contains a concentration of solute that is higher than the saturated point and is called supersaturated.
Returning back to my sugar solution in the jars, when cooled, they were supersaturated. Being in the kitchen and not a laboratory and with a sweet tooth, I couldn’t help but taste some of the solution in the saucepan. It was so incredibly sweet. This time when I placed the lifesavers in the solutions, they didn’t start dissolving upon contact though small crystals were noticed an hour later.
Figure 2: Lifesavers in sugar solutions
This is where I’ve placed the lifesavers:
- Red Lifesaver: Near my desktop computer (small temperature variation)
- Green Lifesaver: The fridge (Cold temperature)
- Orange Lifesaver: At my desk where the morning sun hits warming the area before moving on. (Large temperature variation)
- Yellow Lifesaver: On my dresser where the temperature doesn’t change (constant temperature and also my control sample)
I will keep things as updated as possible. I will be away for eight days due to work commitments which is probably a good thing in terms of recrystallising as the solutions won’t be disturbed but not fantastic on the monitoring of the events.
[Final Notes]: The instructions that I mostly followed: EDUC1706 Class Experiment 1 Growing Sugar Crystals.
