Chapters



Explanations

1.D

Choosing the appropriate instrument is a typical laboratory question on the test. When the question states volumetric analysis and then the word titrated in the same sentence, a burette, choice D, should be your first thought. Choice E is an easy elimination: a balance measures mass in grams and would be used in gravimetric analysis. Choice C is the next elimination: Beakers are not accurate measuring instruments. The markings on a beaker may only be accurate to within a 5–10% range! A pipette, choice B, and a graduated cylinder, choice A, are both very accurate measuring instruments. However, this question discussed a titration, so the best answer is the burette.

2.E

This question requires that you understand the reaction that will occur. In this question, NaOH will react with HCl in a double replacement (neutralization) reaction and produce a salt, NaCl, and water. The concentration of each solution is irrelevant information and is thus ignored. Focus on what the question asks—after drying, what will remain? Statement I is a true statement. If you evaporate all of the water away, NaCl will be the only remaining product. Statement II is a bit tricky. If you read quickly and are thinking law of conservation of matter, you’ll think that this must be false. However, the question states that after drying has occurred, water will evaporate and the mass will be less since some is given off as water vapor. You know then, that the answer contains I and II. Just for confirmation, you could check statement III. This answer is also correct. A metal and a nonmetal bond ionically and salt crystals will be white in color so, E is the answer.

3.B

Answering this question makes you think about physical and chemical changes. You are looking for the one process that is chemical; changing substances, not physical. Chromatography, choice A, is a physical separation of a substance by polarities (as in paper). Filtering, choice C, is also a physical separation of a solid from a liquid. Distillation, choice D, and evaporation, choice E, both involve changes of state, which are also physical changes. Choice B is the only chemical change listed. Precipitation is the formation of a solid when two or more liquids are combined. The formation of a precipitate is one indicator that a chemical change may have taken place.

4.C

Once again, you are in search of the true statements. Statement I is true. If the student forgot to subtract out the mass of the filter paper, the mass obtained would appear larger. Statement II is also correct. If the substance was not completely dry, the moisture would cause the mass to be greater. Statement III is a true statement, but it should not increase the mass of silver unless the student failed to separate all of the silver from the copper before massing. The question states that copper is in excess, meaning that it would not all react. Statement IV, the concentration of the silver nitrate needed to be stronger, does not match the problem—we had too much silver! So the answer is C.

5.A

Choice A is the correct answer. Using a filter paper and funnel, you can easily separate a solid from a liquid. The solid stays in the paper, and the liquid runs through the paper. Choice B would not separate easily using a filter paper. Oil and water would layer and could easily be separated using a pipette. Choice C, two solids, would not separate with filter paper. The easiest separation technique for these two solids would be to use a magnet to gather all of the iron particles. Choice D, gas bubbles, would not be trapped in piece of solid filter paper. To remove the gas, a hose could be attached to the soda, and the soda could be heated or shaken to remove the carbon dioxide gas. Choice E, a mixture of dyes, could be separated with filter paper but not with filtration. The technique to separate the dyes is known as chromatography.

6.D

Color is a result of the way light is reflected. When unshared electrons are present, especially in different energy levels, as is possible with the transition elements and their d orbitals, color is often a result. Most of the color comes in solutions of transition metals. Thus, choice D gives the correct answer. Choices A and B are partial statements of fact but are neither reasons nor explanations. Many solutions of transition elements do contain oxygen in the polyatomic ion, such as nickel (II) nitrate—nitrate contains oxygen, but this has nothing to do with the color. The term metals in statement B is too broad. Over three-quarters of the periodic table is composed of metals, and there are not that many colored solutions! Statement C is also a partially true statement. Most transition metals will be ionically bonded when in salt form, but bond type does not give rise to color. Statement E makes the incorrect assumption that noble gases are all colored. This may have tricked you since you know that neon lights have color. However, the color of the neon light is the direct result of electrons getting excited and falling back to a lower energy level.

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