Q: The separation of compounds on the basis of their solubilities in a given solvent is known as what? Read this paragraph and choose the correct option from the provided answers: Solubility may increase or decrease with temperature; the magnitude of this temperature dependence varies widely among compounds. Notice in particular the curves for NH4NO3 and CaCl2. The dissolution of ammonium nitrate in water is endothermic (Hsoln = +25.7 kJ/mol), whereas the dissolution of calcium chloride is exothermic (Hsoln = 68.2 kJ/mol), yet Figure 13.9 "Solubilities of Several Inorganic and Organic Solids in Water as a Function of Temperature" shows that the solubility of both compounds increases sharply with increasing temperature. In fact, the magnitudes of the changes in both enthalpy and entropy for dissolution are temperature dependent. Because the solubility of a compound is ultimately determined by relatively small differences between large numbers, there is generally no good way to predict how the solubility will vary with temperature. The variation of solubility with temperature has been measured for a wide range of compounds, and the results are published in many standard reference books. Chemists are often able to use this information to separate the components of a mixture byfractional crystallization, the separation of compounds on the basis of their solubilities in a given solvent. For example, if we have a mixture of 150 g of sodium acetate (CH3CO2Na) and 50 g of KBr, we can separate the two compounds by dissolving the mixture in 100 g of water at 80C and then cooling the solution slowly to 0C. According to the temperature curves in Figure 13.9 "Solubilities of Several Inorganic and Organic Solids in Water as a Function of Temperature", both compounds dissolve in water at 80C, and all 50 g of KBr remains in solution at 0C. Only about 36 g of CH3CO2Na are soluble in 100 g of water at 0C, however, so approximately 114 g (150 g 36 g) of Saylor URL: http://www. saylor. org/books. Choices: - nuclei crystallization - simplest crystallization - separate crystallization - fractional crystallization A:
fractional crystallization
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Q: Sodium and chloride ions have equal but what charges? Read this paragraph and choose the correct option from the provided answers: Sodium and chloride ions have equal but opposite charges. Opposite electric charges attract each other, so sodium and chloride ions cling together in a strong ionic bond. You can see this in row 2 of the Figure above . (Brackets separate the ions in the diagram to show that the ions in the compound do not actually share electrons. ) When ionic bonds hold ions together, they form an ionic compound. The compound formed from sodium and chloride ions is named sodium chloride. It is commonly called table salt. You can see an animation of sodium chloride forming at this URL: http://www. visionlearning. com/library/module_viewer. php?mid=55. Choices: - path - positive - simple - opposite A:
opposite
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Q: Which mineral do native americans use to decorate items? Read this paragraph and choose the correct option from the provided answers: Some minerals are valuable simply because they are beautiful. Jade has been used for thousands of years in China. Native Americans have been decorating items with turquoise since ancient times. Minerals like jade, turquoise, diamonds, and emeralds are gemstones. A gemstone is a material that is cut and polished to use in jewelry. Many gemstones, such as those shown in Figure below , are minerals. Choices: - Tanzanite - Topaz - Amethyst - turquoise A:
turquoise
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Q: On what type of land does runoff cause more erosion? Read this paragraph and choose the correct option from the provided answers: Runoff causes more erosion if the land is bare. Plants help hold the soil in place. The runoff water pictured below ( Figure below ) is brown because it eroded soil from a bare, sloping field. Can you find evidence of erosion by runoff where you live? What should you look for?. Choices: - grassy - metallic - mountainous - bare A:
bare
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