... For example, when making rock candy, you dissolve as much sugar as possible in water to make a saturated solution. fsu chemistry site search ... the solution can be "seeded" by adding a small seed crystal of pure sample to the cold solution. The recrystallization of the excess dissolved solvent in a super-saturated solution can be started by inserting a tiny solute crystal, called a seed crystal. Document your observations, including the temperature of the air. This can be tricky; a pair of tweezers will help! For example, halite indicates a cubic structure. Stirring prevents the sugar crystals that start to form from growing too big. A supersaturated solution is a solution that contains more than the average solvent that can be dissolved at a given temperature. Chemistry Science Fair Project: Investigate how using a seed crystal changes the growth rate of sugar crystals when making rock candy. 2. If you need to, you can score a groove in the crystal to hold the line in place. The method is named after the Polish scientist Jan Czochralski, who developed it in 1916. The rate of crystallization in Equation $$\ref{13.2.1}$$ is greater than the rate of dissolution, so crystals or a precipitate form (Figure $$\PageIndex{1d}$$). Stirring causes the sucrose molecules to be pushed into one another, forming crystal seeds … If no crystals form upon cooling, you may have used too much solvent, and should evaporate some of … These small crystals will be used as the "seed" crystals for each group. Get someone to help you tie the fishing line to the seed crystal. Once a tiny crystal forms, it serves as a nucleation point. The sugar clinging to the string or stick serves as a seed crystal. Make sure each group has the following materials: a 250-mL beaker or 9-oz plastic cup, a coffee stirrer or pencil, a piece of nylon or cotton string 15 to 20 cm long, and a hand lens. pattern based on its unique chemistry and molecular alignment causing a distinct shape. Another example of crystallizing salt out of a supersaturated solution can be seen in the following video. References: This seed crystal also forms a surface for the solid to crystallize upon. Demonstration can be performed one of two ways. Continue inspecting your crystals in the saucer and in the super saturated solution. Rock salt (halite), sugar (sucrose), borax (sodium borate) and alum all show a crystal structure when precipitated from a super-saturated solution. This first phase is called nucleation. This will initiate crystallization of the solution. In general, a crystal grows from a “crystal seed,” which is a clump of sucrose molecules, a speck of dust, or a gas bubble. Divide your class into groups of 3 to 4 students each. Slowly pour the supersaturated solution on top of the seed crystals. Terms/Concepts: Crystals; Super-saturation; Polycrystalline mass; Molecular patterns; Crystal habit; Seed crystal; Crystal growth. In this case, a supersaturated solution of sodium acetate is poured over a crystal of sodium acetate. These crystals provide the lattice structure "seed" which … Sugar molecules crystallize in a solution when they bump into each other and stick together. First, a seed crystal can be added to the beaker (or flask) and crystallization can be initiated in this manner. Remove the biggest and best-looking of the small crystals from the saucer to use as your seed crystal. Secondly, seed crystals can be placed onto a watch glass. This is a crystal that promotes the growth of the bigger crystals of the rock candy. Consequently, adding a small particle of the solute, a seed crystal, will usually cause the excess solute to rapidly precipitate or crystallize, sometimes with spectacular results. Crystals may differ in size, but each has its own structure. 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