Q: How many atoms are present in $$2.00$$ moles of helium gas?

$$1.20 \times 10$$^{24}$$ atoms

Question 1

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

Accepted Answer

An exact number is obtained by counting or defined relationships, while a measured number is obtained using a measuring device and has uncertainty.

Question 2

A student measures the mass of a metal cylinder as $$12.34\ \mathrm{g}$$ and its volume as $$4.56\ \mathrm{cm}^3. $$What is the density of the cylinder, and how many significant figures should the answer have?

Accepted Answer

$$2.706\ \mathrm{g/cm}^3$$, 4 significant figures

Question 3

Which of the following is the correct symbol and meaning for the metric prefix 'nano-'?

Accepted Answer

$$n$$, $$10^{-9}$$

Question 4

A sample contains $$3.01 	imes 10$$^{23}$$ molecules of water. How many moles of water does this represent?

Accepted Answer

$$0.500$$ mol

Question 5

Which of the following best describes the difference between an isotope and an ion?

Accepted Answer

Isotopes have the same number of protons but different numbers of neutrons; ions have the same number of protons but different numbers of electrons.

Question 6

Which scientist is credited with discovering the electron using cathode ray experiments?

Accepted Answer

J.J. Thomson

Question 7

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

Accepted Answer

$$\mathrm{CH}_2\mathrm{O}$$

Question 8

Which of the following is the correct name for the compound $$\mathrm{FeCl}_3$$?

Accepted Answer

Iron(III) chloride

Question 9

A student needs to convert $$250.0\ \mathrm{mL} of a $$solution to liters. What is the correct conversion and how many significant figures should the answer have?

Accepted Answer

$$0.2500\ \mathrm{L}$$, 4 significant figures

Question 10

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group have the same number of valence electrons.

Question 11

A sample of magnesium contains three isotopes: $$^{24}\mathrm{Mg} (78.99$$%, mass = 23.985 amu), $$^{25}\mathrm{Mg} (10.00$$%, mass = 24.986 amu), and $$^{26}\mathrm{Mg} (11.01$$%, mass = 25.983 amu). What is the average atomic mass of magnesium?

Accepted Answer

$$24.31$$ amu

Question 12

Which of the following is a chemical property?

Accepted Answer

Reactivity with oxygen

Question 13

A patient receives an intravenous solution containing $$0.90\%$$ NaCl by mass. If the solution has a total mass of $$500\ \mathrm{g}$$, how many grams of NaCl are present?

Accepted Answer

$$45\ \mathrm{g}$$

Question 14

Which of the following best describes the process of dimensional analysis?

Accepted Answer

Using conversion factors to systematically solve problems involving unit changes.

Question 15

How many atoms are present in $$2.00$$ moles of helium gas?

Accepted Answer

$$1.20 	imes 10$$^{24}$$ atoms

Question 16

Which of the following compounds is an ionic compound?

Accepted Answer

$$\mathrm{NaCl}$$

Question 17

A student dissolves $$5.00\ \mathrm{g} of $$glucose ($$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6) in $$enough water to make $$100.0\ \mathrm{mL} of $$solution. What is the molarity of the solution? (Molar mass of glucose = $$180.16\ \mathrm{g/mol})$$

Accepted Answer

$$0.278\ \mathrm{mol/L}$$

Question 18

Which of the following is the correct empirical formula for a compound with $$62.1\% C$$, $$10.4\% H$$, and $$27.5\% O by $$mass?

Accepted Answer

$$\mathrm{C}_3\mathrm{H}_6\mathrm{O}$$

Question 19

Which of the following best describes a heterogeneous mixture?

Accepted Answer

A mixture in which the individual components remain distinct and can be seen as separate phases

Question 20

Which of the following ions is isoelectronic with neon ($$\mathrm{Ne}$$)?

Accepted Answer

$$\mathrm{Na}^+$$

CHEM 141 Exam 1: Study Notes on Matter, Atoms, and Molecules

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