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Ebook Chemistry experiments: Part 2

(BQ) Part 2 book "Chemistry experiments" has contents: Microscale percent composition, levels of sugar, thin layer chromatography, the rate of rusting, chloride levels, heat energy, chemical moles, finding molar mass, endothermic and exothermic reactions, solutions and spectrophotometry. | 11. Solutions and Spectrophotometry Topic A spectrophotometer can be used to analyze the transmission of light through different solutions. Introduction Solutions are types of homogenous mixtures in which one substance, the solute, is dissolved in a solvent. Solutions can be described as concentrated, where there is a large amount of solute dissolved in a solvent, or dilute, where there is a small amount of solute. However, these descriptions are qualitative and are generally not very precise. Solutions can also be described quantitatively by using molarity (M), the number of moles (mol) of solute per liter of solution. A solution with a high molarity is more concentrated than one with a low molarity. Many chemical solutions are transparent, and the molarity cannot be known simply by looking at the solutions’ color. However, with some solutions, the color of the solution changes as the concentration changes. In these cases, the solutions can be analyzed using a spectrophotometer (Figure 1a). Inside a spectrophotometer, a beam of light passes through a monochromator, a device that changes the beam so that it is made up of only one wavelength of light. This modified beam travels through the sample to be tested, which is held in a cuvette, a thin glass tube. A sensor on the other side of the sample detects the light, and the device calculates the amount of light that is transmitted and the amount absorbed by the solution (Figure 1b). In this experiment, you will create copper (II) sulfate solutions of known concentrations, then test their absorbance using a spectrophotometer. You will use your data to create a graph of concentration versus light absorbance. Then, using the graph you created, you will determine the concentration of an unknown solution of copper (II) sulfate. Time Required 60 minutes 74 © 2011 Facts on File. All Rights Reserved. 11. Solutions and Spectrophotometry 75 digital status readout .