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

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

Q: Which of the following conversions is set up correctly using dimensional analysis to convert $$5.00\ \mathrm{g} of $$carbon to moles? (Molar mass of carbon $$= 12.01\ \mathrm{g/mol})$$

$$5.00\ \mathrm{g} \times \frac{1\ \mathrm{mol}}{12.01\ \mathrm{g}}$$

Question 1

A sample of seawater is analyzed in a laboratory. Which of the following best describes seawater?

Accepted Answer

A mixture, because it contains various dissolved salts and water that can be separated physically.

Question 2

A mixture of sand and salt is best separated by which method, and why?

Accepted Answer

Filtration, because sand is insoluble in water and can be separated from dissolved salt.

Question 3

Which of the following is a chemical property?

Accepted Answer

Ability of iron to rust when exposed to air.

Question 4

A block of metal has a mass of $$54.0\ \mathrm{g}$$ and a volume of $$20.0\ \mathrm{cm}^3. $$What is its density?

Accepted Answer

$$2.70\ \mathrm{g/cm}^3$$

Question 5

Calculate the number of significant figures in the result of the following calculation: $$3.45 	imes 0.0340$$

Accepted Answer

2

Question 6

Convert $$250.0\ \mathrm{mL} to $$liters using dimensional analysis.

Accepted Answer

$$0.250\ \mathrm{L}$$

Question 7

A compound contains $$12.0\ \mathrm{g} of $$carbon and $$32.0\ \mathrm{g} of $$oxygen. What is the percent composition of oxygen in the compound?

Accepted Answer

$$72.7\%$$

Question 8

An atom has 17 protons, 18 neutrons, and 18 electrons. Which of the following statements is correct?

Accepted Answer

It is a chloride ion with a $$-1$$ charge.

Question 9

Which of the following is an isotope of $$^{14}\mathrm{C}$$?

Accepted Answer

An atom with 6 protons and 7 neutrons.

Question 10

Which of the following elements is a metalloid?

Accepted Answer

Silicon ($$\mathrm{Si})$$

Question 11

What is the most likely charge of an ion formed by an atom of magnesium ($$\mathrm{Mg}$$)?

Accepted Answer

$$+2$$

Question 12

A sample of element X is analyzed by mass spectrometry and found to contain $$60\%$$ $$^{63}\mathrm{X} ($$mass $$= 63.0\ \mathrm{u}) $$and $$40\%$$ $$^{65}\mathrm{X} ($$mass $$= 65.0\ \mathrm{u}). $$What is the average atomic mass of X?

Accepted Answer

$$64.0\ \mathrm{u}$$

Question 13

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

Accepted Answer

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

Question 14

A student mixes $$50.0\ \mathrm{mL} of $$water (density $$= 1.00\ \mathrm{g/mL}) $$with $$50.0\ \mathrm{mL} of $$ethanol (density $$= 0.789\ \mathrm{g/mL}). $$What is the total mass of the mixture?

Accepted Answer

$$89.5\ \mathrm{g}$$

Question 15

Which of the following changes is a physical change?

Accepted Answer

Dissolving sugar in water.

Question 16

A student needs to prepare $$0.500\ \mathrm{mol} of $$sodium chloride ($$\mathrm{NaCl}). $$What mass of $$\mathrm{NaCl} is $$required? (Molar mass $$= 58.44\ \mathrm{g/mol})$$

Accepted Answer

$$29.22\ \mathrm{g}$$

Question 17

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

Accepted Answer

A compound always contains the same elements in the same ratio by mass.

Question 18

A sample of an unknown element contains atoms with 20 protons, 20 neutrons, and 18 electrons. Which statement is correct?

Accepted Answer

It is a $$+2$$ cation of calcium, since it has lost 2 electrons.

Question 19

Which of the following conversions is set up correctly using dimensional analysis to convert $$5.00\ \mathrm{g} of $$carbon to moles? (Molar mass of carbon $$= 12.01\ \mathrm{g/mol})$$

Accepted Answer

$$5.00\ \mathrm{g} 	imes \frac{1\ \mathrm{mol}}{12.01\ \mathrm{g}}$$

Question 20

A student calculates the density of a liquid as $$0.876\ \mathrm{g/mL}$$ using a mass of $$43.8\ \mathrm{g}$$ and a volume of $$50.0\ \mathrm{mL}. $$How many significant figures should the answer have?

Accepted Answer

3

Fundamental Concepts in General Chemistry: Classification, Properties, and Quantitative Relationships

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