Q: A graphite pencil tip weighs 15 mg. How many carbon atoms does it contain? (Molar mass of C = 12.01 g/mol, $$1\ \mathrm{mol} = 6.022 \times 10$$^{23}$$ atoms)

$$7.52 \times 10$$^{20}$$ atoms

Q: Which of the following is the correct conversion factor for changing grams to moles for a given element?

$$\frac{1\ \mathrm{mol}}{\text{molar mass in g}}$$

Question 1

A student measures the mass of a sample three times using a bathroom scale and a lab scale. The bathroom scale gives readings of 0.1 kg, 0.0 kg, and 0.1 kg, while the lab scale gives 54.4 g, 54.5 g, and 54.3 g. Which statement best explains the difference in the measurements?

Accepted Answer

The lab scale is more precise because it gives more consistent and detailed measurements.

Question 2

Which of the following best describes how to determine the number of significant figures in a measurement?

Accepted Answer

Count all the digits you are sure of plus one estimated digit.

Question 3

You add 18 L of water to 0.01315 L more. What is the correct sum, expressed with appropriate significant figures?

Accepted Answer

$$18.01\ \mathrm{L}$$

Question 4

A car uses 11.70 gallons of gasoline to drive 278 miles. What is the gas mileage, in miles per gallon, reported with the correct number of significant figures?

Accepted Answer

$$23.8\ \mathrm{mi/gal}$$

Question 5

Which of the following is the correct rule for determining the number of significant figures in the result of a multiplication or division?

Accepted Answer

The result should have as many significant figures as the number with the fewest significant figures.

Question 6

Which of the following is the correct rule for determining the number of significant figures in the result of an addition or subtraction?

Accepted Answer

The result should have as many decimal places as the number with the fewest decimal places.

Question 7

A graphite pencil tip weighs 15 mg. How many carbon atoms does it contain? (Molar mass of C = 12.01 g/mol, $$1\ \mathrm{mol} = 6.022 	imes 10$$^{23}$$ atoms)

Accepted Answer

$$7.52 	imes 10$$^{20}$$ atoms

Question 8

Which of the following best explains why the atomic mass of chlorine on the periodic table is not a whole number?

Accepted Answer

It is a weighted average of the masses of all naturally occurring isotopes.

Question 9

Given that chlorine has two naturally occurring isotopes: chlorine-35 (mass = 34.969 amu, abundance = 75.76%) and chlorine-37 (mass = 36.966 amu, abundance = 24.24%), what is the average atomic mass of chlorine?

Accepted Answer

$$35.45\ \mathrm{amu}$$

Question 10

Which of the following best describes Avogadro's number?

Accepted Answer

The number of atoms in one mole of a substance.

Question 11

If 2.258 $$	imes$$ $$10^{22}$$ atoms of silicon have a mass of 1.05 g, what is the molar mass of silicon?

Accepted Answer

$$28.0\ \mathrm{g/mol}$$

Question 12

Which of the following is the correct definition of an atomic mass unit (amu)?

Accepted Answer

One twelfth the mass of a carbon-12 atom.

Question 13

A sample contains $$3.01 	imes 10$$^{23}$$ atoms of copper. What is the mass of this sample? (Molar mass of Cu = 63.55 g/mol)

Accepted Answer

$$31.8\ \mathrm{g}$$

Question 14

Which of the following best explains why different samples of helium, sulfur, copper, and magnesium containing 1 mole each do not have the same mass?

Accepted Answer

Each element has a different atomic mass, so 1 mole of each has a different mass.

Question 15

Which of the following is the correct conversion factor for changing grams to moles for a given element?

Accepted Answer

$$\frac{1\ \mathrm{mol}}{	ext{molar mass in g}}$$

Question 16

A student is asked to solve the following equation for $$x$$: $$(36.20 - x)(5.4 	imes 10^3$)(1.869) = 21584. $$What is the value of $$x$$, rounded to the correct number of significant figures?

Accepted Answer

$$34.1$$

Question 17

Which of the following best describes the relationship between precision and significant figures in a measurement?

Accepted Answer

A measurement with more significant figures is more precise.

Fundamental Math and Physics Concepts in General Chemistry

Guida di studio - Domande di pratica

Study guide - Flashcard