APC 4.1-4.4

A student had two dilute, colorless solutions, HCl (aq) and NaOH(aq), which were at the same temperature. The student combined the solutions, and the reaction represented above occurred. Which of the following results would be evidence that a chemical reaction took place?

• The resulting solution is colorless

• The temperature of the mixture increases.

• The total volume of the mixture is approximately equal to the sum of the initial volumes.

• The resulting solution conducts electricity.

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4.1

A student was asked to formulate a hypothesis about what would happen if 100. ml of 0.1M NaOH(aq) at 25°C was combined with 100. ml of 0.1M MgCl2(aq) at 25°C. Which of the following hypotheses indicates that the student thought a chemical change would occur?

• The volume of the resulting solution will be equal to the sum of the volumes of the original solutions.

• The mass of the resulting solution will be equal to the sum of the masses of the original solutions.

• The resulting solution would contain a precipitate.

• The resulting solution will be clear.

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4.1

A student was studying physical and chemical changes. The student carried out some procedures in the laboratory and recorded observations. For one of the procedures, the student concluded that a physical change took place, but not a chemical change. Which of the following could have been the results of the procedure?

• A cube of metal was changed into a flat sheet of metal.

• When two liquids at room temperature were combined in a beaker, the beaker became hot.

• When two clear liquids were combined, the resulting mixture was cloudy.

• When a colorless liquid was added to a blue liquid, the resulting solution was yellow.

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4.1

Which of the following is the net ionic equation for the reaction between aqueous sodium fluoride and hydrochloric acid?

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4.2

Equal volumes of 0.2⁢M solutions of lead(II) nitrate and potassium bromide are combined to form lead(II) bromide as a yellow precipitate. Which of the following is the correct net ionic equation for the reaction?

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4.2

The reaction between aqueous strontium chloride (SrCl2) and aqueous potassium sulfate (K2SO4) forms a precipitate of strontium sulfate (SrSO4). Which of the following represents the net ionic equation for the reaction?

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4.2

A student places a sample of a pure metal in a crucible and heats it strongly in air. Data from the experiment are given in the table above. The final mass was determined after the sample was cooled to room temperature. Which of the following statements related to the experiment is correct?

• • The mass of the sample decreased, so physical changes occurred as the metal first melted and then boiled out of the crucible.

    The mass of the sample decreased, so physical changes occurred as the metal first melted and then boiled out of the crucible.

• The mass of the sample increased, so a chemical change occurred when bonds formed between the metal and another substance.

• There was nothing for the metal to react with, so only a physical change could have occurred.

• The sample was only heated, so neither a physical nor a chemical change occurred.

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4.4

A student mixes 20.0g of white KCl crystals with distilled water in a beaker. After the mixture was stirred, no crystals are visible and the solution is clear. After several days, all of the water evaporates and white crystals are found in the beaker. Which of following pieces of experimental evidence would best help the student to confirm that a new compound had not been made and that only a physical change occurred?

• The solution does not change color after stirring.

• The KCl crystals are no longer visible after mixing with water.

• There is a temperature change in the solution during the dissolving process.

• After the water has evaporated, the white crystals in the beaker have a mass of 20.0g.

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4.4

The table above summarizes data given to a student to evaluate the type of change that took place when substance X was mixed with water. The student claimed that the data did not provide enough evidence to determine whether a chemical or physical change took place and that additional tests were needed. Which of the following identifies the best way to gather evidence to support the type of change that occurred when water and X were mixed?

• Measuring the melting point of the mixture of water and X

• Adding another substance to the mixture of water and X to see whether a solid forms

• Measuring and comparing the masses of the water, X, and the mixture of water and X

• Measuring the electrical conductivities of X and the mixture of water and X

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4.4