Answer the following question given this paragraph: You won't see this car on the road, at least not yet. It's a concept car that was developed by a major automaker. Instead of burning gasoline, it runs on hydrogen gas. Using hydrogen for fuel doesn't produce pollution, and it doesn't depend on nonrenewable fossil fuels. New technologies like this car may one day help solve our energy resource problems. But even without new technologies such as this, there are many ways we can help solve the problems right now. Q: Developing cars that run on hydrogen gas can help solve our dependence on what? Choices: - oxygen - food - water - nonrenewable fossil fuels A:
nonrenewable fossil fuels
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Answer the following question given this paragraph: 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 CH3CO2Na crystallizes out on cooling. The crystals can then be separated by filtration. Thus fractional crystallization allows us to recover about 75% of the original CH3CO2Na in essentially pure form in only one step. Fractional crystallization is a common technique for purifying compounds as diverse as those shown in Figure 13.9 "Solubilities of Several Inorganic and Organic Solids in Water as a Function of Temperature" and from antibiotics to enzymes. For the technique to work properly, the compound of interest must be more soluble at high temperature than at low temperature, so that lowering the temperature causes it to crystallize out of solution. In addition, the impurities must be more soluble than the compound of interest (as was KBr in this example) and preferably... Q: What is the separation of compounds on the basis of their solubilities in a given solvent? Choices: - solvent law - fractional mass - volatile crystallization - fractional crystallization A:
fractional crystallization
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Answer the following question given this paragraph: Eukaryotes evolved about 2 billion years ago. Unlike prokaryotes, eukaryotes have a cell nucleus. They have more structures and are better organized. Organelles within a eukaryote can perform certain functions. Some supply energy; some break down wastes. Eukaryotes were better able to live and so became the dominant life form. Q: Unlike prokaryotes, eukaryotes have what? Choices: - cell membrane - golgi apparatus - cell wall - cell nucleus A:
cell nucleus
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Answer the following question given this paragraph: Plants maintain the atmosphere. They produce oxygen and absorb carbon dioxide during photosynthesis. Oxygen is essential for cellular respiration for all aerobic organisms. It also maintains the ozone layer that helps protect Earth's life from damaging UV radiation. Removal of carbon dioxide from the atmosphere reduces the greenhouse effect and global warming. Q: The ozone layer protects the earth from what? Choices: - pollution - light waves - radio waves - uv radiation A:
uv radiation
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