 Sodium chloride is the main constituent in table salt. Its production is mainly through the evaporation of brine pools and mining of natural halite deposits. The ionic compound forms a cubic crystal structure called rock salt, or halite structure, in which chlorine ions form an FCC lattice with sodium ions located in octahedral interstitials. In this laboratory video, we will gross sodium chloride crystals on glass substrates through evaporation. The preferential growth direction will be determined using x-ray diffraction. This will be compared to the XRD pattern of powder sodium chloride. In this example, we grow crystals from a one molar sodium chloride solution, but students can change this concentration to see if it affects crystal formation. First, we will calculate the mass of sodium chloride needed to prepare a one molar solution. The formula weight is located on the container as 58.44 grams per mole. Therefore, the volume times the molarity times the molar mass will give us the required mass of sodium chloride. We can check this using dimensional analysis. The units of liters cancel. Units of moles cancel, which leaves units of grams. The result is 2.92 grams, which will be added to 50 milliliters of water. A special note should be made here. Dissolving salt and water will change its final volume. Therefore, the concentration is not exactly one mole per liter. Instead, we should call this one molal solution. Molality is the concentration of solute per kilogram of solvent. At low concentrations, molarity and molality are nearly the same, but the difference increases at higher concentrations. What would be the correct procedure of preparing a one molar solution? Sodium chloride is weighed into a plastic weigh boat on a digital scale. The plastic weigh boat is placed onto the scale and its tear weight is removed by pressing the tear button. A metal spatula is used to add 2.92 grams of sodium chloride. 50 milliliters of deionized water is prepared using a graduated cylinder. The volume is measured to the bottom of the meniscus. The water is added to a glass beaker with PTFE coated magnetic stir rod. The beaker is placed onto a stir plate and turned on. The salt is added to the water. The sodium chloride is allowed to completely dissolve. Now the sodium chloride solution is ready to be deposited onto a glass substrate using a transfer pipette. Students can experiment with different substrates to see what effect it has on crystal growth. Samples are now allowed to dry. This example dries samples at 80 degrees Celsius in the air. Students can also investigate how different drying temperatures or humidities can affect crystal growth. Now sodium chloride powder is prepared for XRD. Sodium chloride crystals are crushed into powder using a motor and pestle. After a sufficiently small powder is made, it is added to an XRD sample holder. It is carefully added and spread around so that the top surface is flush with the top of the sample holder. The sample holder must retain its powder sample when tilted to high angles. The sodium chloride droplets have evaporated within 24 hours. Millimeter sized flat square crystals have grown on the glass substrate. XRD will be used to determine the preferred orientation of crystals grown on this substrate. The glass substrate and sample are adhered onto a sample holder using polymer clay. The top surface of the grown crystals are positioned to the same plane as the top surface of the sample holder. Both samples are characterized using XRD. These are the measured diffraction patterns for the powder sample and grown crystals. The data will be provided for students to graph and analyze. Based on this information, what can you conclude about the preferred orientation of crystal growth from evaporating salt solution on glass slides?