15.

Question

(01.04 MC)

Sue classified some substances as shown in the table.

Sue's Table
Good Conductors of Heat Bad Conductors of Heat
Silver Cotton
Copper Wool
Cork Air

Why is Sue's table incorrect? (4 points)

Air is a good conductor of heat.

Wool is a good conductor of heat.

Cork is a bad conductor of heat.

Copper is a bad conductor of heat.
16.
(01.05 MC)

A group of students is investigating whether copper is a better thermal conductor than aluminum. The students take a copper wire and an aluminum wire of the same length and diameter. They put equal lengths of wax on one end of each wire and dip the other ends into a beaker of hot water. The length of wax left on the wires after 10 minutes is shown.

Experimental Observations
Copper Aluminum
Original length of wax 2 cm 2 cm
Length of wax after 10 minutes 0.7 cm 1.2 cm

What was the independent variable in this experiment? (4 points)

Final length of wax

Type of wire used

Original length of wires

Thermal conductivity of wire
17.
(01.04 HC)

The table shows the mass and density of some substances.

Density of Substances
Mass
(g) Density of Iron
(g/cm3) Density of Silver
(g/cm3)
100 7.8 19.3
200 P Q

Part 1: Is the value of Q less than, greater than, or equal to the value of P?
Part 2: Explain your answer for Part 1. (8 points)

18.
(01.05 HC)

Sasha did an experiment to study the solubility of two substances. She poured 100 mL of water at 20 °C into each of two beakers labeled A and B. She put 50 g of Substance A in the beaker labeled A and 50 g of Substance B in the beaker labeled B. The solution in both beakers was stirred for 1 minute. The amount of substance left undissolved in the beakers was weighed. The experiment was repeated for different temperatures of water and the observations were recorded as shown.

Experimental Observations
Substance Mass of Undissolved Substance at Different Temperatures (gram)
20 °C 40 °C 60 °C 80 °C
A 12 11 9 8
B 45 40 34 31

Part 1: Which substance has a higher solubility?
Part 2: Explain your answer for Part 1. (8 points)

Answer 1

Question 15

Sue's table is incorrect primarily because it misclassifies certain materials based on their thermal conductivity.

Correct Answer: Cork is a bad conductor of heat.

Explanation: Cork is indeed classified correctly as a bad conductor of heat in Sue's table. However, the other materials also need clarification: air is a poor conductor, not a good one; wool is a bad conductor, and copper is a good conductor. The confusion here is potentially in that air cannot conduct heat well, and thus Sue’s classification doesn't reflect the accurate properties of materials listed.

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Question 16

The independent variable in this experiment is:

Correct Answer: Type of wire used.

Explanation: The independent variable is the factor that is intentionally changed or manipulated in the experiment to observe its effect. Here, the students are specifically comparing copper wire to aluminum wire to see which one conducts heat better, thus the type of wire is what is manipulated.

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Question 17

Part 1: The value of Q is less than the value of P.

Part 2: This can be explained by the relationship between mass and density. Density is calculated using the formula:

\[ Density = \frac{Mass}{Volume} \]

Given that the mass of iron and silver in the table is presented with their densities, we can derive that for a greater density (like that of silver), the corresponding volume must be smaller for the same mass. Since the mass of 200 g is to be used for both iron and silver, the density of silver will result in a smaller volume than that of iron (which has a density of 7.8 g/cm³). Therefore, Q, which represents the density of silver for the 200 g mass, must be greater than P, which represents the density of iron, indicating that 19.3 g/cm³ (the density of silver) results in a smaller volume than 7.8 g/cm³ (the density of iron).

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Question 18

Part 1: Substance A has a higher solubility.

Part 2: This conclusion can be drawn from the experimental observations reported. As the temperature of water increases, the amount of undissolved substance decreases for Substance A, indicating that it dissolves more effectively as the temperature rises, with only 8 g remaining undissolved at 80 °C. In contrast, Substance B remains largely undissolved at higher temperatures, with 31 g left at 80 °C. The lower undissolved mass of Substance A across all recorded temperatures indicates that it has a higher overall solubility compared to Substance B.