Q: A sample of a compound contains 12 g of carbon, 2 g of hydrogen, and 16 g of oxygen. What is the mass percent of carbon in the compound? Use the formula $$\text{Mass \%}=\frac{\text{mass of element}}{\text{total mass}}\times100.$$

$$\frac{12}{30}\times100=40\%$$

Question 1

Which of the following statements best describes the difference between an atom and a molecule?

Accepted Answer

An atom is the smallest basic unit of an element, while a molecule is two or more atoms chemically bonded together.

Question 2

Which of the following is an example of a heterogeneous mixture?

Accepted Answer

Oil and water

Question 3

A student heats a sample of water and observes that it boils at 100°C. Which type of property is being measured?

Accepted Answer

Physical property

Question 4

Which separation technique would be most appropriate to separate a mixture of sand and salt water?

Accepted Answer

Filtration

Question 5

A sample of a compound contains 12 g of carbon, 2 g of hydrogen, and 16 g of oxygen. What is the mass percent of carbon in the compound? Use the formula $$	ext{Mass \%}=\frac{	ext{mass of element}}{	ext{total mass}}	imes100.$$

Accepted Answer

$$\frac{12}{30}	imes100=40\%$$

Question 6

Which of the following statements about isotopes is correct?

Accepted Answer

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

Question 7

A neutral atom of magnesium (Mg) has an atomic number of 12 and a mass number of 24. How many neutrons does it have?

Accepted Answer

12

Question 8

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 9

Which of the following is a cation?

Accepted Answer

Na⁺

Question 10

How many molecules are present in 2.00 moles of water ($$\mathrm{H_2O}$$)? Use Avogadro's number: $$6.022\$$times10^{23}$$.

Accepted Answer

$$1.20\$$times10^{24}$$

Question 11

Which of the following compounds is an example of an ionic compound?

Accepted Answer

NaCl

Question 12

What is the empirical formula for a compound containing 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass?

Accepted Answer

CH₂O

Question 13

Which of the following is a physical change?

Accepted Answer

Ice melting

Question 14

A student measures the mass of a sample three times and gets values very close to each other, but far from the true value. This is an example of:

Accepted Answer

Low accuracy, high precision

Question 15

Which of the following elements is a halogen?

Accepted Answer

Chlorine (Cl)

Question 16

Calculate the density of a liquid if its mass is 25.0 g and its volume is 10.0 mL. Use $$D=\frac{m}{V}.$$

Accepted Answer

$$2.5\ \mathrm{g/mL}$$

Question 17

Which of the following is a molecular element?

Accepted Answer

O₂

Question 18

What is the formula mass of $$\mathrm{CO_2$}$$? (C = 12.01, O = 16.00)

Accepted Answer

$$12.01 + 2(16.00) = 44.01\ \mathrm{g/mol}$$

Question 19

Which of the following best describes a chemical property?

Accepted Answer

Flammability

Question 20

A sample contains $$3.01\$$times10^{23}$$ molecules of $$\mathrm{$$NH_3$$}$$. How many moles of $$\mathrm{$$NH_3$$}$$ are present? Use Avogadro's number: 6.022$$\$$times10^{23}.$$

Accepted Answer

0.500 mol

General Chemistry Study Notes: Matter, Atoms, and Molecules

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