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Day 28 Item Analysis

Day 28 Item Analysis. Each beaker shown below contains one liter of water. One hundred grams of sugar is added to each beaker. In which beaker will the sugar dissolve the fastest?. The correct answer is A. The sugar added to this beaker is composed of

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Day 28 Item Analysis

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  1. Day 28 Item Analysis

  2. Each beaker shown below contains one liter of water. One hundred grams of sugar is added to each beaker. In which beaker will the sugar dissolve the fastest?

  3. The correct answer is A. The sugar added to this beaker is composed of small granules, so it has a large total surface area. The greater the surface area of the particles, the faster they will dissolve. In addition, the solution is being stirred with a stirring rod. Stirring brings more water in contact with the surface of the sugar, which increases the dissolving rate. Finally, the water in this beaker is hot. For solid solutes such as sugar, increasing the temperature increases the rate at which the solute dissolves.

  4. A teacher has prepared a saturated solution of potassium nitrate (KNO3) in 100 grams of water heated to 60ºC. About how many grams of potassium nitrate will have settled out of the solution once it reaches a room temperature of 25ºC? A 30 g B 65 g C 95 g D 145 g

  5. The correct answer is B. The graph shows that the solubility of KNO3 decreases as the temperature decreases. At 60ºC a saturated solution can hold about 95 grams of KNO3 per 100 grams of water. At 25ºC a saturated solution can hold only about 30 grams of KNO3 per 100 grams of water. To find the mass of KNO3 that settles out of the solution, find the difference between the solubilities: 95 g – 30 g = 65 g So about 65 grams of KNO3 will have settled out

  6. If each of these bottles of carbonated water initially contained the same amount of dissolved carbon dioxide, which bottle will contain the least amount of dissolved carbon dioxide after 15 minutes?A Bottle 1 B Bottle 2 C Bottle 3 D Bottle 4

  7. The correct answer is D The pressure in a sealed container Bottle 4 is uncapped, so the carbon dioxide in Bottle 4 is under less pressure than the carbon dioxide in Bottles 1 and 2. Because the solubility of a gas decreases as the pressure decreases, Bottle 4 will contain less carbon dioxide than Bottles 1 and 2. In addition, Bottle 4 sits in warm water, unlike Bottle 3, which is chilled. Because the solubility of a gas decreases as the temperature increases, Bottle 4 will contain less carbon dioxide than Bottle 3.

  8. Thermal pollution occurs when human activities cause the temperature of lakes or rivers to rise. Why are fish most likely to be harmed by long-term thermal pollution of the lake in which they live? A The solubility of oxygen in the lake will decrease. B The solubility of carbon dioxide in the lake will increase. C The solubility of potassium fertilizers, such as KCl, will decrease in the lake. D The solubility of quartz crystals (SiO2) will increase in the lake.

  9. The correct answer is The solubility of a gas in water decreases as the temperature increases. As thermal pollution causes the temperature of the lake to rise, the amount of oxygen dissolved in the lake will decrease. Fish need dissolved oxygen in order to survive, so they may be negatively affected by such a change. To get this question correct, it is important to read the question carefully and to understand how temperature affects the solubility of a gas.

  10. 5. What is one way to distinguish a solution of salt (NaCl) and water from a solution of sugar (C6H12O6) and water without tasting them? A The salt can be recovered by evaporating the water, but the sugar cannot. B The salt solution will conduct electric current, but the sugar solution will not. C The sugar can be separated from the water by filtration, but the salt cannot. D A beam of light passing through the sugar solution will be visible, but a beam of light passing through the salt solution will not.

  11. The correct answer isB. Salt is an ionic compound, so when salt dissolves in water, the solute (salt) exists as ions. For this reason, a salt solution will conduct an electric current. By contrast, sugar is a covalent compound. When sugar dissolves in water, the solute (sugar) exists as neutral molecules. As a result, a sugar solution will not conduct an electric current.

  12. Scuba divers are exposed to greater pressure the deeper they dive. Which is most likely to occur as a result of this increased pressure? A Glucose will become much more soluble in divers’ cells. B A high level of nitrogen gas will dissolve in divers’ bloodstream. C Small bubbles of carbon dioxide will form in divers’ bloodstream. D The amount of oxygen dissolved in divers’ cells will sharply decrease.

  13. The correct answer is B. The solubility of gases increases with an increase in pressure. Therefore, the solubility of nitrogen gas in the divers’ blood will increase as the divers are exposed to high pressure underwater.

  14. When added to the beaker, which liquid would cause the lightbulb to glow the brightest? A A concentrated solution of water and table sugar B A concentrated solution of water and nitrogen gas C A dilute solution of water and ammonia D A dilute solution of water and sulfuric acid

  15. The correct answer is D. The lightbulb will glow only if electric current can pass from one electrode to the other. The solution will conduct electricity from one electrode to another only if it contains ions. The more ions the solution contains, the better it can conduct electricity. When a strong acid such as sulfuric acid is added to water, almost all of the acid molecules break up into ions, so a solution of sulfuric acid is a good conductor of electricity. The lightbulb in this circuit should glow brightly when a solution of sulfuric acid is added to the beaker.

  16. Over time an open soft drink will lose carbonation (dissolved CO2). Which of these allows the CO2 to remain in solution the longest? A Reduced air pressure B Exposure to direct sunlight C Increased air currents D Cooler temperatures

  17. The correct answer is D. • The solubility of a gas decreases with a decrease in pressure and an increase in temperature. Since the bottle is open the pressure has decreased. To keep the gas soluble, the temperature must be decreased. Cool temperatures will keep carbon dioxide dissolved the longest.

  18. Bathwater normally has electrolytic behaviors even though distilled water does not. This is because bathwater — A contains isotopes of hydrogen B has been heated C is separated into H+ and OH– ions D contains dissolved minerals

  19. The correct answer is D. • Tap water contains dissolved minerals such as Ca+2, Cl-1, Na+1, and CO3-2. The presence of ions in solution give the solution electrolytic properties. Distilled water contains only water. There are no dissolved ions in distilled water. It does not conduct.

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