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Chemistry Regents June 2010 - Question 83 |
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Written by The Chemistry Wizard
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Answer: One physical property of aluminum that would make it better than copper for a cooking pan would be its weight.
Why? Aluminum has a much lower atomic weight than copper, however it has a larger atomic radius. Copper has an atomic weight of approximately 63 and an atomic volume of approximately 7cm3/mol, Aluminum on the other hand has an atomic weight of 27 and an atomic volume of 10cm3/mol. Aluminum would be much more easily handled in the kitchen as it would give good thermal conductivity, but would be much lighter than copper.
The question also stated that copper was 3.3 times the density of aluminum, making it heavier in the process. |
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Chemistry Regents June 2010 - Question 82 |
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Written by The Chemistry Wizard
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Answer: Copper is malleable, ductile, a good conductor of heat and less susceptible to corrosion.
Malleable - This means copper can be bent and twisted without breaking. Other metals capable of this are gold and silver.
Ductile - This means it can be stretched to thin tubules, usually for the purpose of making electrical wiring.
Copper is an excellent conductor of heat. For this reason it is often used in the manufacturer of cooking utensils.
Copper is also less susceptible to corrosion. Copper will readily form a protective barrier of copper oxide; this will prevent any further breakdown of copper. |
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Chemistry Regents June 2010 - Question 68 |
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Written by The Chemistry Wizard
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Answer: A laboratory procedure to recover the solid solute would be crystallization by means of evaporation.
Place the solution into a beaker or crucible
Place the container with the solution over a heat source (flame or heating element)
Allow the solution to come to a boil and continue to boil until all the liquid has evaporated
As a result of the evaporation process, no water would be present, leaving the KNO3(s) in its place. Step 3 in the process removes the polar solvent (water), which is responsible for the separation of the salt into its ionic forms. The result is solid KNO3 as the forces of attraction between the ionic anion and cation are too great and form a solid salt. |
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Chemistry Regents June 2010 - Question 66 |
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Written by The Chemistry Wizard
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Answer: The boiling point of the solution is expected to be higher than the boiling point of water. The solution would have stronger forces of attraction as a result of ionic interactions, while simple Van Der Waals forces would be holding the water molecules together. Ionic forces of attraction are far stronger than Van Der Waals forces. |
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Chemistry Regents June 2010 - Question 48 |
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Written by The Chemistry Wizard
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Answer: (3)
Why? An electrolyte is any ionic solution capable of conducting an electrical current. Typically, this means most electrolytes are acids, bases or salts in solution. The main function of an electrolyte is to dissociate to allow for the neutralizing of the electrons being produced at the anode and being consumed at the cathode. In that respect, an electrolyte must be able to dissociate to form an anion (negatively charged ion) and a cation (positively charged ion). Electrolytes will dissociate in water, as water molecules are dipoles and will orient themselves in a manner that is suitable to solvate the ions.
Answering the Question:
To answer this question knowledge of the definition of an electrolyte is helpful. Answer (1) suggests the pH of aqueous potassium chloride as a test to determine whether or not it is an electrolyte. The power of hydrogen (pH) is used as a measure of acidity or basicity in aqueous solutions and not a measure of conductivity. Therefore, answer (2) would also be eliminated as it, too, suggests pH as a method of determination.
Answer (3) suggests the electrical conductivity of aqueous potassium chloride. To determine whether or not potassium chloride is an electrolyte, it would have to be dissolved in water or molten. The (aq) indicates that potassium chloride is dissolved in water. This is important, as an electrolyte will conduct not from the flow of electrons but instead as a result of a chemical reaction. Answer (4) suggests the conductivity of solid potassium chloride. As KCl is a bonded compound with no free electrons (in metals), then it would not be expected to conduct an electrical current. This leaves answer (3) as the only possible answer. |
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Chemistry Regents June 2010 - Question 42 |
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Written by The Chemistry Wizard
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Answer: (?) |
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Chemistry Regents June 2010 - Question 41 |
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Written by The Chemistry Wizard
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Answer: (2)
Why? The ideal gas law tries to explain the relationship of different factors on the behavior of the theoretical ideal gas.
In essence pV = nRT, where; p is absolute pressure, V is the volume, n is the number of moles of the gas, T is temperature and R is the universal gas constant.
Based on the relationship defined in the equation pV=nRT, volume (V) and temperature (T) are directly proportional. This means that as volume increases, so will temperature, or as temperature increases so will volume if in both cases pressure remains constant. Because the relationship is a linear one, it also means that, as volume doubles, all other factors being constant, temperature will also double.
Answering the Question:
To answer this question it helps to have an understanding of the behavior of gases and the relationship of pressure, temperature and pressure. Answers (1) and (3), as they propose an inverse relationship between temperature and volume, would not be correct. Based on the equation defining the ideal gas pV=nRT, there is a directly proportional relationship between volume and temperature. The ideal gas law is also based on absolute temperature; the unit for absolute temperature is specified in Kelvin (K). Although Kelvin and Celsius increase by the same degree, they have different values. Using kelvin as the unit means that answer (2) is a better answer than answer (4), as it uses the unit K rather than °C. If knowledge of the gas law and hence equation, was not known, then answers (2) and (4) would have been a good starting point. It is generally known that increasing temperature causes most substances to expand. This could be assumed to hold true for gases, also eliminating answers (1) and (3). This would increase the probability of choosing the correct answer from answers (2) and (4). Answer (2) is the correct answer. |
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Chemistry Regents June 2010 - Question 39 |
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Written by The Chemistry Wizard
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Answer: (1)
Why? Vapor pressure is the pressure of a gas in equilibrium above its liquid or solid phase in a closed system. When a liquid boils, it is because the temperature reached has caused the vapor pressure to equals atmospheric pressure. Vapor pressure increases with increasing temperature in a non-linear manner. However, the degree of increase in vapor pressure can normally be linked to the boiling point of the compound. Such that, compounds with lower boiling points will have a higher vapor pressure with increasing temperature than compounds with higher boiling points. SO compounds with higher boiling points will always have the lower vapor pressure as temperature increases.
Reason for Answer: To answer this question, it is important to know the boiling points of the given compounds. Answer (1) is ethanoic acid, which has a boiling point of 118°C. Answer (2), ethanol, has a boiling point of 79°C. Answer (3), propanone, has a boiling point of 56°C and answer (4), water has a boiling point of 100°C. Ethanoic acid has the highest boiling point of the listed compounds and hence is a safe answer to choose for the lowest vapor pressure at 50°C. Therefore, the answer is answer (1), ethanoic acid. |
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Chemistry Regents June 2010 - Question 20 |
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Written by The Chemistry Wizard
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Answer: (4)
Why? The equation is that of a reversible reaction in equilibrium, this means that the forward reaction and the reverse reaction are both proceeding at the same rate. This result is no net change in the mass of H2O in either phase. A reversible reaction in equilibrium will have no net change in reactants or products unless some external factor comes to play. For example unless there was a change in temperature, pressure, contaminants or some other such factor.
A reversible reaction in equilibrium however, does not mean that the mass or concentration of the reactant and product are equal, just that they are constant. So there could be significantly more H2O(l) than H2O(s) for example, however the ratio of each remains constant. If either the product or the reactant starts to be produced more rapidly, then the system is no longer in equilibrium.
Answering the Question:
To answer this question all that needs to be understood is the concept of equilibrium. The term equilibrium does not mean equal but that there is no change in the amount of reactant or product. Therefore any answer, which does not describe this, would be the incorrect answer. Answer (1) says the H2O(s) is melting faster than the H2O(l). This means that there is a change in the amount of both forms of H2O, implying that the system is not in equilibrium. Answer (2) has a similar issue to answer (1) in that one part of the process is occurring faster than the other. In this case the H2O(l) is freezing faster than the H2O(s) can melt. This means that eventually only frozen H2O would be present. Answer (3) speaks to equivalence and not equilibrium, leaving answer (4) which says that whatever the amount of each form of H2O there is no change in that mass. |
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Chemistry Regents June 2010 - Question 18 |
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Written by The Chemistry Wizard
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Answer: (4)
Why? An ideal gas is described as a set of randomly moving non-interacting particles. The ideal gas is composed mostly of empty space such that the volume of the individual particles is negligible. The ideal gas is a theory of what a gas should be like if it were to be the perfect gas. This means it would have to behave most like a gas and least like a liquid or solid. As a result the forces of attraction between the particles would be non-existent in an ideal gas and that would impact its behavior, causing it to behave closer to a liquid or solid.
Answering the Question:
To answer the question it would be easier to have an understanding of what makes a gas a gas. As such answer (1) would not be correct, as the particles are said to be moving in a well-defined, circular path. A well-defined state of movement does not occur for particles occurring in nature. Answer (2) suggests that particles in an ideal gas release energy. This would imply that as gases collide, the temperature of the system would decrease, as energy is lost. A decrease in energy of the system would cause the system to stop behaving like an ideal gas. The closer the energy contained in atoms gets to absolute zero, the more solid the element becomes. Answer (3) suggests that there are forces of attraction between particles. The concept of an ideal gas is that in order for the particles to move randomly and not interact, there should be no forces of attraction between them. Therefore, (4) is the correct answer as it does meet the requirements of an ideal gas, in that the volume of the particle is negligible with respect to the volume of empty space in the system. |
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