Q: Which of the following is a correct example of dimensional analysis for converting $$25$$ inches to centimeters? (Use $$1\ \mathrm{in} = 2.54\ \mathrm{cm})$$

$$25\ \mathrm{in} \times \frac{2.54\ \mathrm{cm}}{1\ \mathrm{in}} = 63.5\ \mathrm{cm}$$

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 counted and has no uncertainty, while a measured number is determined by measurement and has uncertainty.

Question 2

A student measures the mass of a metal sample as 45.67 g and its volume as 12.3 mL. What is the density of the metal, reported with the correct number of significant figures?

Accepted Answer

The density is $$3.71 g/mL.$$

Question 3

Which metric prefix represents $$10^{-6}$$?

Accepted Answer

micro-

Question 4

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

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

Question 5

Which of the following is a derived SI unit?

Accepted Answer

joule ($$\mathrm{J})$$

Question 6

A sample contains $$2.50 	imes 10$$^{23}$$ molecules of water. How many moles of water are present?

Accepted Answer

$$0.415$$ mol

Question 7

Which scientist is credited with proposing the first modern atomic theory based on experimental evidence?

Accepted Answer

John Dalton

Question 8

A neutral atom of magnesium has an atomic number of $$12$$ and a mass number of $$24. $$How many neutrons does it contain?

Accepted Answer

$$12$$ neutrons

Question 9

Which of the following is the correct name for the compound $$\mathrm{Na}_2\mathrm{SO}_4$$?

Accepted Answer

Sodium sulfate

Question 10

A student needs to convert $$5.0$$ kilometers to centimeters. Which conversion factor should be used, and what is the correct answer?

Accepted Answer

Use $$1\ \mathrm{km} = 1000\ \mathrm{m}$$ and $$1\ \mathrm{m} = 100\ \mathrm{cm}$$; answer: $$500,000\ \mathrm{cm}$$

Question 11

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 12

A sample of chlorine contains $$75.77\%$$ $$^{35}\mathrm{Cl} ($$mass $$34.969$$ amu) and $$24.23\%$$ $$^{37}\mathrm{Cl} ($$mass $$36.966$$ amu). What is the average atomic mass of chlorine?

Accepted Answer

$$35.45$$ amu

Question 13

Which of the following is a correct example of dimensional analysis for converting $$25$$ inches to centimeters? (Use $$1\ \mathrm{in} = 2.54\ \mathrm{cm})$$

Accepted Answer

$$25\ \mathrm{in} 	imes \frac{2.54\ \mathrm{cm}}{1\ \mathrm{in}} = 63.5\ \mathrm{cm}$$

Question 14

Which group on the periodic table contains elements that are all chemically inert under normal conditions?

Accepted Answer

Group 18 (noble gases)

Question 15

A $$50.0 mL $$sample of ethanol has a mass of $$39.5 g. $$What is the percent by mass of ethanol if the total solution mass is $$100.0 g$$?

Accepted Answer

$$39.5\%$$

Question 16

Which of the following ions is correctly paired with its charge?

Accepted Answer

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

Question 17

A sample of glucose ($$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6) $$weighs $$18.0 g. $$What is the number of moles of glucose in the sample? (Molar mass $$= 180.0 g/$$mol)

Accepted Answer

$$0.10$$ mol

Question 18

Which of the following best describes the classification of air?

Accepted Answer

Air is a homogeneous mixture.

Question 19

A student mixes $$10.0 g of $$sodium chloride with $$90.0 g of $$water. What is the percent by mass of sodium chloride in the solution?

Accepted Answer

$$10.0\%$$

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

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