Q: A sample of natural gas (methane) reacts with 96 g of oxygen to produce 66 g of carbon dioxide. According to the Law of Conservation of Mass, how many grams of water are produced?

$$\text{Total mass of reactants} = \text{Total mass of products}$$ $$21 + 96 = 66 + x \implies x = 51\ \text{g}$$

Q: Which of the following is the correct formula to calculate the weighted average atomic mass of an element with two isotopes?

$$\text{(fractional abundance of isotope 1)} \times (\text{mass of isotope 1}) + \text{(fractional abundance of isotope 2)} \times (\text{mass of isotope 2})$$

Q: Which of the following is the correct conversion for $$1000\ \text{mm} to $$meters?

$$1000\ \text{mm} = 1\ \text{m}$$

Question 1

Which of the following best describes the Law of Conservation of Mass?

Accepted Answer

The total mass of reactants equals the total mass of products in a chemical reaction.

Question 2

A sample of natural gas (methane) reacts with 96 g of oxygen to produce 66 g of carbon dioxide. According to the Law of Conservation of Mass, how many grams of water are produced?

Accepted Answer

$$	ext{Total mass of reactants} = 	ext{Total mass of products}$$
$$21 + 96 = 66 + x \implies x = 51\ 	ext{g}$$

Question 3

Which of the following is a chemical change?

Accepted Answer

Burning wood to form ash and gases

Question 4

Convert $$3.45 	imes 10^4$ to standard notation.

Accepted Answer

$$34,500$$

Question 5

Which of the following best describes an endothermic reaction?

Accepted Answer

A reaction that absorbs heat from the surroundings

Question 6

A block has a mass of $$15.0\ 	ext{g}$$ and a volume of $$3.0\ 	ext{mL}. $$What is its density?

Accepted Answer

$$5.0\ 	ext{g/mL}$$

Question 7

Which of the following is a property of metals?

Accepted Answer

Malleable and good conductor of electricity

Question 8

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 9

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

Accepted Answer

$$12 ($$since $$24 - 12 = 12)$$

Question 10

Which of the following is the correct formula to calculate the weighted average atomic mass of an element with two isotopes?

Accepted Answer

$$	ext{(fractional abundance of isotope 1)} 	imes (	ext{mass of isotope 1}) + 	ext{(fractional abundance of isotope 2)} 	imes (	ext{mass of isotope 2})$$

Question 11

Which of the following is a correct example of a cation?

Accepted Answer

$$	ext{Na}^+$$

Question 12

Which of the following best describes a heterogeneous mixture?

Accepted Answer

A mixture in which the components are not evenly distributed and can be distinguished easily

Question 13

Which of the following is the correct conversion for $$1000\ 	ext{mm} to $$meters?

Accepted Answer

$$1000\ 	ext{mm} = 1\ 	ext{m}$$

Question 14

Which of the following is a property of noble gases?

Accepted Answer

Chemically inert and exist as gases at room temperature

Question 15

A student measures the temperature of a solution as $$25.0\ ^\circ	ext{C}. $$What is this temperature in Kelvin?

Accepted Answer

$$298.2\ 	ext{K}$$

Question 16

Which of the following best describes a physical property?

Accepted Answer

Color

Question 17

Which of the following is the correct number of significant figures in the measurement $$0.03450$$?

Accepted Answer

4

Question 18

Which of the following best describes the difference between a compound and a mixture?

Accepted Answer

A compound has a fixed composition and chemical bonds between elements, while a mixture does not.

Question 19

Which of the following is the correct definition of atomic number?

Accepted Answer

The number of protons in an atom

Question 20

A sample contains $$70.0\%$$ isotope A (mass $$84.9118\ 	ext{amu}) $$and $$30.0\%$$ isotope B (mass $$86.9092\ 	ext{amu}). $$What is the average atomic mass?

Accepted Answer

$$(0.7 	imes 84.9118) + (0.3 	imes 86.9092) = 85.57\ 	ext{amu}$$

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