Q: A student needs to convert $$5.00\ \mathrm{km} to$$ $$\mathrm{cm}. $$Which of the following is the correct dimensional analysis setup?

$$5.00\ \mathrm{km} \times \frac{10^3$\ \mathrm{m}}{1\ \mathrm{km}} \times \frac{100\ \mathrm{cm}}{1\ \mathrm{m}}$$

Q: Which of the following is the correct setup to calculate the average atomic mass of chlorine, given $$75.77\%$$ $$\mathrm{^{35}Cl}$$ ($$34.97\ \mathrm{amu}) $$and $$24.23\%$$ $$\mathrm{^{37}Cl}$$ ($$36.97\ \mathrm{amu}$$)?

$$(0.7577 \times 34.97) + (0.2423 \times 36.97)$$

Question 1

A sample of ethanol has a mass of 46.0 g and occupies a volume of 58.0 mL. What is the density of ethanol in $$\mathrm{g/mL}$$, and which metric prefix best describes this value?

Accepted Answer

$$0.79\ \mathrm{g/mL}$$; milli-

Question 2

Which of the following statements about significant figures is correct when multiplying $$2.50 ($$three sig figs) by $$0.040 ($$two sig figs)?

Accepted Answer

The answer should have two significant figures.

Question 3

A student needs to convert $$5.00\ \mathrm{km} to$$ $$\mathrm{cm}. $$Which of the following is the correct dimensional analysis setup?

Accepted Answer

$$5.00\ \mathrm{km} 	imes \frac{10^3$\ \mathrm{m}}{1\ \mathrm{km}} 	imes \frac{100\ \mathrm{cm}}{1\ \mathrm{m}}$$

Question 4

Which of the following is an example of a derived SI unit?

Accepted Answer

$$\mathrm{m^3$} ($$cubic meter)

Question 5

A compound contains $$40.0\%$$ carbon, $$6.7\%$$ hydrogen, and $$53.3\%$$ oxygen by mass. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{CH_2O}$$

Question 6

Which scientist is credited with the discovery of the electron using the cathode ray tube experiment?

Accepted Answer

J.J. Thomson

Question 7

A neutral atom of sodium ($$\mathrm{Na}) $$has an atomic number of $$11$$ and a mass number of $$23. $$How many protons, neutrons, and electrons does it have?

Accepted Answer

11 protons, 12 neutrons, 11 electrons

Question 8

Which of the following best describes the difference between an exact number and a measured number?

Accepted Answer

Exact numbers have no uncertainty; measured numbers have uncertainty.

Question 9

A sample contains $$3.00\ \mathrm{mol} of$$ $$\mathrm{H_2O}. $$What is the mass of the sample in grams? ($$\mathrm{M_{H_2O}} = 18.0\ \mathrm{g/mol})$$

Accepted Answer

$$54.0\ \mathrm{g}$$

Question 10

Which of the following ions is correctly named?

Accepted Answer

$$\mathrm{Na^+}$$: sodium ion

Question 11

A student mixes $$50.0\ \mathrm{mL} of $$water (density $$= 1.00\ \mathrm{g/mL}) $$with $$50.0\ \mathrm{mL} of $$ethanol (density $$= 0.79\ \mathrm{g/mL}). $$What is the total mass of the mixture?

Accepted Answer

$$89.5\ \mathrm{g}$$

Question 12

Which of the following is the correct percent composition by mass of nitrogen in $$\mathrm{NH_3$}$$? ($$\mathrm{M_{NH_3$}} = 17.0\ \mathrm{g/mol}$$, $$\mathrm{M_N} = 14.0\ \mathrm{g/mol})$$

Accepted Answer

$$82.4\%$$

Question 13

Which of the following elements is a member of the alkaline earth metals group?

Accepted Answer

Magnesium ($$\mathrm{Mg})$$

Question 14

A compound has a molar mass of $$58.0\ \mathrm{g/mol}$$ and an empirical formula of $$\mathrm{C_2H_5}$$ ($$\mathrm{M_{C_2H_5}} = 29.0\ \mathrm{g/mol}). $$What is its molecular formula?

Accepted Answer

$$\mathrm{C_4H_{10}}$$

Question 15

Which of the following best describes the classification of air?

Accepted Answer

A homogeneous mixture

Question 16

Which of the following is the correct setup to calculate the average atomic mass of chlorine, given $$75.77\%$$ $$\mathrm{^{35}Cl}$$ ($$34.97\ \mathrm{amu}) $$and $$24.23\%$$ $$\mathrm{^{37}Cl}$$ ($$36.97\ \mathrm{amu}$$)?

Accepted Answer

$$(0.7577 	imes 34.97) + (0.2423 	imes 36.97)$$

Question 17

Which of the following is the correct name for $$\mathrm{$$FeCl_3$$}$$?

Accepted Answer

Iron(III) chloride

Question 18

A patient receives $$250\ \mathrm{mg} of a $$medication. How many grams is this?

Accepted Answer

$$0.250\ \mathrm{g}$$

Question 19

Which of the following best explains why isotopes of an element have different mass numbers?

Accepted Answer

They have different numbers of neutrons.

Question 20

A student is given a sample of a compound and determines its empirical formula is $$\mathrm{CH}. If $$the molar mass of the compound is $$78.0\ \mathrm{g/mol}$$, what is its molecular formula?

Accepted Answer

$$\mathrm{C_6H_6}$$

CHEM 141 Exam 1 Study Guide: Matter, Atoms, and Molecules

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