Q: A sample of copper metal has a mass of 5.00 g. The atomic radius of copper is approximately $$1.28 \times 10$$^{-10}$$ m. Assuming copper atoms are spherical and packed without empty space, estimate the number of copper atoms in the sample. (Molar mass of Cu = 63.55 g/mol, Avogadro's number N_A = 6.022$$ \times $$10^{23}$$ mol$$^{-1})$$

$$4.74 \times 10$$^{22}$$ atoms

Q: How many atoms are present in 0.250 mol of neon gas? ($$N_A = 6.022 \times 10$$^{23}$$ mol$$^{-1}$$)

$$1.51 \times 10$$^{23}$$ atoms

Question 1

A sample of copper metal has a mass of 5.00 g. The atomic radius of copper is approximately $$1.28 	imes 10$$^{-10}$$ m. Assuming copper atoms are spherical and packed without empty space, estimate the number of copper atoms in the sample. (Molar mass of Cu = 63.55 g/mol, Avogadro's number N_A = 6.022$$ 	imes $$10^{23}$$ mol$$^{-1})$$

Accepted Answer

$$4.74 	imes 10$$^{22}$$ atoms

Question 2

Given the isotope symbol $$^{37}_{17}\mathrm{Cl}^-$$, determine the number of protons, neutrons, and electrons in this ion.

Accepted Answer

17 protons, 20 neutrons, 18 electrons

Question 3

Boron has two naturally occurring isotopes: $$^{10}\mathrm{B} ($$mass = 10.0129 amu, abundance = 19.9%) and $$^{11}\mathrm{B} ($$mass = 11.0093 amu, abundance = 80.1%). Calculate the atomic weight of boron.

Accepted Answer

$$10.81$$ amu

Question 4

How many moles of water molecules are present in 36.0 g of $$\mathrm{H}_2\mathrm{O}$$? (Molar mass of $$\mathrm{H}_2\mathrm{O} = 18.0 g/$$mol)

Accepted Answer

2.00 mol

Question 5

A mass spectrum of magnesium shows three peaks at masses 24, 25, and 26 with relative intensities of 79%, 10%, and 11%, respectively. Calculate the atomic weight of magnesium.

Accepted Answer

$$24.32$$ amu

Question 6

Which of the following is a pure substance?

Accepted Answer

Carbon dioxide gas ($$\mathrm{CO}_2)$$

Question 7

Which of the following is the correct chemical formula for a compound represented by a ball-and-stick model showing two hydrogen atoms bonded to one oxygen atom?

Accepted Answer

$$\mathrm{H}_2\mathrm{O}$$

Question 8

Classify the bond in sodium chloride ($$\mathrm{NaCl}).$$

Accepted Answer

Ionic

Question 9

What is the number of electrons in a $$\mathrm{Fe}^{3+}$$ ion?

Accepted Answer

24

Question 10

Which of the following molecular representations corresponds to the chemical formula $$\mathrm{CaCl}_2$$?

Accepted Answer

One large sphere (Ca) connected to two smaller spheres (Cl)

Question 11

What is the correct name for the compound $$\mathrm{K}_2\mathrm{SO}_4$$?

Accepted Answer

Potassium sulfate

Question 12

What is the chemical formula for magnesium nitride?

Accepted Answer

$$\mathrm{Mg}_3\mathrm{N}_2$$

Question 13

Which of the following is the correct name for $$\mathrm{PCl}_5$$?

Accepted Answer

Phosphorus pentachloride

Question 14

How many atoms are present in 0.250 mol of neon gas? ($$N_A = 6.022 	imes 10$$^{23}$$ mol$$^{-1}$$)

Accepted Answer

$$1.51 	imes 10$$^{23}$$ atoms

Question 15

A sample contains 3.01 $$	imes$$ $$10^{23}$$ molecules of $$\mathrm{CO}_2. $$What is the mass of this sample? (Molar mass of $$\mathrm{CO}_2 = 44.0 g/$$mol)

Accepted Answer

22.0 g

Question 16

Which of the following best describes brass?

Accepted Answer

A mixture

Question 17

Which of the following is a binary molecular compound?

Accepted Answer

$$\mathrm{N}_2\mathrm{O}_4$$

Question 18

Given the formula $$\mathrm{Al}_2\mathrm{O}_3$$, what is the correct name for this compound?

Accepted Answer

Aluminum oxide

Question 19

Which of the following statements is true regarding the conversion between structural formulas and chemical formulas?

Accepted Answer

A structural formula shows the arrangement of atoms, while a chemical formula shows only the types and numbers of atoms.

Question 20

Which of the following best describes the matter in a can of soda (before opening)?

Accepted Answer

A mixture

Fundamental Concepts in Atomic Structure, Isotopes, and Chemical Compounds

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