Q: How many atoms of zinc are in $$25.4\ \mathrm{mg} of $$zinc? (Molar mass of Zn = $$65.38\ \mathrm{g/mol}$$, $$1\ \mathrm{mol} = 6.022 \times 10$$^{23}$$ atoms)

$$2.34 \times 10$$^{20}$$ atoms

Q: How many atoms are in $$12.75\ \mathrm{g} of $$iron? (Molar mass of Fe = $$55.85\ \mathrm{g/mol}$$, $$1\ \mathrm{mol} = 6.022 \times 10$$^{23}$$ atoms)

$$1.38 \times 10$$^{23}$$ atoms

Question 1

According to the Law of Conservation of Mass, if 150.0 grams of aluminum oxide ($$\mathrm{Al_2O_3}) is $$decomposed and produces 77.115 grams of aluminum metal, how many grams of oxygen gas are produced? (Use the equation: $$2\mathrm{Al_2O_3} \rightarrow 3\mathrm{O_2$} + 4\mathrm{Al})$$

Accepted Answer

$$72.885\ \mathrm{g}$$

Question 2

Which of the following best illustrates the Law of Definite Proportions?

Accepted Answer

Water from any source always contains hydrogen and oxygen in a $$2:1$$ atom ratio.

Question 3

A sample of $$\mathrm{C_2H_{12}}$$ reacts with oxygen to produce $$298.61\ \mathrm{g} of$$ $$\mathrm{CO_2$}$$ and $$146.62\ \mathrm{g} of$$ $$\mathrm{H_2O}. $$How many grams of oxygen gas were consumed? (Use the equation: $$\mathrm{C_2H_{12}} + 8\mathrm{O_2$} \rightarrow 5\mathrm{CO_2$} + 6\mathrm{H_2O})$$

Accepted Answer

$$232.88\ \mathrm{g}$$

Question 4

Which of the following statements about isotopes is correct?

Accepted Answer

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

Question 5

Given the isotope $$^{80}_{35}\mathrm{Br}$$, how many neutrons does it have?

Accepted Answer

$$45$$

Question 6

Which element is classified as a transition metal and is found in period 6, group 10 of the periodic table?

Accepted Answer

Platinum ($$\mathrm{Pt})$$

Question 7

What is the charge and symbol for the ion formed by calcium?

Accepted Answer

$$\mathrm{Ca$$^{2+}$$}$$

Question 8

A sample contains $$2.06 	imes 10$$^{22}$$ atoms of carbon. How many moles of carbon are present? (1$$\ 	ext{mol} = 6.022 	imes $$10^{23}$$ atoms)

Accepted Answer

$$0.0342\ \mathrm{mol}$$

Question 9

What is the mass in grams of $$2.91$$ moles of gold? (Molar mass of Au = $$197.0\ \mathrm{g/mol})$$

Accepted Answer

$$573.27\ \mathrm{g}$$

Question 10

How many atoms of zinc are in $$25.4\ \mathrm{mg} of $$zinc? (Molar mass of Zn = $$65.38\ \mathrm{g/mol}$$, $$1\ \mathrm{mol} = 6.022 	imes 10$$^{23}$$ atoms)

Accepted Answer

$$2.34 	imes 10$$^{20}$$ atoms

Question 11

Which of the following best describes a cation?

Accepted Answer

A positively charged ion formed when an atom loses electrons.

Question 12

A chlorine sample contains $$75.77\%$$ $$^{35}\mathrm{Cl} ($$atomic mass $$34.96885$$ amu) and $$24.23\%$$ $$^{37}\mathrm{Cl} ($$atomic mass $$36.96590$$ amu). What is the average atomic mass of chlorine?

Accepted Answer

$$35.45\ \mathrm{amu}$$

Question 13

Which of the following is the correct composition by mass for glucose ($$\mathrm{C_6H_{12}O_6$}$$)? (Atomic masses: C = $$12.01$$, H = $$1.008$$, O = $$16.00)$$

Accepted Answer

C: $$40.00\%$$, H: $$6.71\%$$, O: $$53.29\%$$

Question 14

If you have $$1.85\ \mathrm{g} of $$cesium (Cs), how many moles do you have? (Molar mass of Cs = $$132.91\ \mathrm{g/mol})$$

Accepted Answer

$$0.0139\ \mathrm{mol}$$

Question 15

Which of the following elements is a metalloid?

Accepted Answer

Germanium ($$\mathrm{Ge})$$

Question 16

A $$100.0\ \mathrm{g}$$ sample of two compounds containing only C, H, and O yields the following upon decomposition: Compound 1: $$52.13\ \mathrm{g} C$$, $$13.15\ \mathrm{g} H$$, $$34.72\ \mathrm{g} O$$; Compound 2: $$54.52\ \mathrm{g} C$$, $$9.169\ \mathrm{g} H$$, $$36.31\ \mathrm{g} O. $$What is the ratio of H to O in Compound 1?

Accepted Answer

$$0.379$$

Question 17

Which of the following best describes the Law of Multiple Proportions?

Accepted Answer

When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.

Question 18

Which isotope of magnesium is the most abundant in nature?

Accepted Answer

$$^{24}\mathrm{Mg}$$

Question 19

How many atoms are in $$12.75\ \mathrm{g} of $$iron? (Molar mass of Fe = $$55.85\ \mathrm{g/mol}$$, $$1\ \mathrm{mol} = 6.022 	imes 10$$^{23}$$ atoms)

Accepted Answer

$$1.38 	imes 10$$^{23}$$ atoms

Atoms, Elements, and the Foundations of General Chemistry

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