Video Transcript
Some students put a single cube of sugar into five different beakers. They fill the beakers with 100 milliliters of tepid water. One of the beakers is stirred vigorously. It is stirred for 60 seconds. The other beakers are stirred for three to five seconds each. Which of these figures represents the beaker that was stirred for 60 seconds? The blue spheres represent water molecules and the red spheres represent sugar molecules. (A) 1, (B) 2, (C) 3, (D) 4, or (E) 5.
For these five different beakers, we are given a particle view of the water molecules and the sugar molecules so that we can compare the effects of the stirring. Each beaker contains 100 milliliters of water and a single sugar cube. The water in all five beakers is tepid, Which means the temperature in all beakers is approximately the same and is only slightly warm. While all five beakers are stirred, only one beaker is stirred for 60 seconds, while the other four beakers are stirred for anywhere between three and five seconds. We must use the views of the particles provided of the sugar and water molecules in the beakers to determine which beaker was stirred for 60 seconds. Let’s clear some space on screen to find the correct figure.
This question deals with the solubility of the sugar cube. Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a given temperature. In other words, it is the ability of a substance to dissolve and completely mix with another substance. In this case, the solute or the substance being dissolved is the sugar cube and the solvent is the water. The rate at which the solute or the sugar cube dissolves is called the rate of dissolution. The rate of dissolution can be changed by particle size, temperature, and stirring. Since all five beakers had the same particle size of the sugar cube and the same tepid water, the only change used here to manipulate the rate of dissolution would be stirring.
Let’s have a closer look at how stirring a solution impacts the rate of dissolving the solute. If we stir a solution in an effort to dissolve a solute in a solvent, as was done in the five beakers, we can increase the rate of dissolution by increasing the interactions between solute and solvent particles. If we stir the solution for only a short amount of time, we will cause only a few more solute–solvent interactions. However, if we stir the solution for a longer amount of time, more and more particle interactions between solute and solvent will occur, which will speed up the rate of dissolution. Therefore, stirring for longer periods of time can help dissolve the solute more quickly and distribute solute particles throughout the solvent.
The figure that most closely resembles our particle view of longer stirring time is figure 1. Figure 1 shows the sugar molecules distributed in greater amount throughout the water molecules, whereas the rest of the figures show only a few sugar molecules distributed through many water molecules. Therefore, figure 1 is the correct answer. So the figure that represents the beaker that was stirred for 60 seconds is answer choice (A), 1.
