Q: How many atoms are in 2.54 mol of helium?

$$1.53 \times 10$$^{24}$$ atoms

Q: A sample of gold ($$Au) $$weighs $$145 g. $$How many gold atoms are in this sample? (Molar mass of $$Au = 197.0 g/$$mol)

$$4.43 \times 10$$^{23}$$ atoms

Question 1

Which scientist is credited with formulating the law of conservation of mass, and what does this law state?

Accepted Answer

Lavoisier; it states that the total mass before and after a chemical reaction remains unchanged.

Question 2

According to Dalton’s atomic theory, which statement is correct?

Accepted Answer

Atoms of each element are unique and combine in whole number ratios to form compounds.

Question 3

Which law explains why water from different sources always has the same ratio of hydrogen to oxygen atoms?

Accepted Answer

Law of constant composition

Question 4

A sample of mercury(II) oxide (HgO) contains 100.0 g of mercury and 7.98 g of oxygen. A sample of mercury(I) oxide (Hg2O) contains 100.0 g of mercury and 3.99 g of oxygen. What law does this data illustrate?

Accepted Answer

Law of multiple proportions

Question 5

Which model of the atom was proposed after the discovery of the electron, and what did it suggest about atomic structure?

Accepted Answer

Plum pudding model; atoms are positive spheres with embedded negative electrons.

Question 6

Which experiment led to the discovery of the nucleus, and what was the key observation?

Accepted Answer

Rutherford gold foil experiment; some alpha particles were deflected at large angles.

Question 7

What is the charge and location of a neutron in an atom?

Accepted Answer

Charge 0, located in the nucleus.

Question 8

Which equation represents Coulomb’s law for the force between two charged particles?

Accepted Answer

$$F_e = k_e \frac{|q_1$ q_2$|}{r^2$}$$

Question 9

Which statement about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 10

How is the average atomic weight of an element calculated?

Accepted Answer

By multiplying the mass of each isotope by its decimal abundance and summing the results.

Question 11

What is the formula mass of carbon dioxide ($$CO_2) in $$amu?

Accepted Answer

$$44.01$$ amu

Question 12

What is the percent composition of oxygen in $$K_2CO_3$$? (Formula mass = $$138.23$$ amu, oxygen mass = $$3 	imes 16.00$$ amu)

Accepted Answer

$$34.73\%$$

Question 13

How many atoms are in 2.54 mol of helium?

Accepted Answer

$$1.53 	imes 10$$^{24}$$ atoms

Question 14

A 1 carat diamond contains $$1.0 	imes 10$$^{22}$$ carbon atoms. How many moles of carbon is this?

Accepted Answer

$$0.017$$ mol

Question 15

What is the mass in grams of a $$1.73$$ mol sample of neon ($$Ne$$)? (Molar mass of $$Ne = 20.18 g/$$mol)

Accepted Answer

$$34.91 g$$

Question 16

A sample of table salt ($$NaCl) $$has a mass of $$15.3 g. $$How many moles of $$NaCl$$ comprise this sample? (Molar mass of $$NaCl = 58.44 g/$$mol)

Accepted Answer

$$0.262$$ mol

Question 17

A sample of gold ($$Au) $$weighs $$145 g. $$How many gold atoms are in this sample? (Molar mass of $$Au = 197.0 g/$$mol)

Accepted Answer

$$4.43 	imes 10$$^{23}$$ atoms

Question 18

A sample of table sugar ($$C_{12}H$$_{22}$$O_{11}) $$weighs $$200 g. $$How many oxygen atoms are in this sample? (Molar mass of $$C_{12}H$$_{22}$$O_{11} = 342 g/$$mol)

Accepted Answer

$$3.90 	imes 10$$^{24}$$ atoms

Question 19

Which statement best describes the relationship between protons and electrons in a neutral atom?

Accepted Answer

The number of protons equals the number of electrons.

Atoms and Elements: Foundations of General Chemistry

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