Q: Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

$$\text{Average mass} = (\text{fraction}_1 \times \text{mass}_1) + (\text{fraction}_2 \times \text{mass}_2)$$

Q: How many atoms are present in 2.00 mol of copper ($$Cu$$)? ($$N_A = 6.022 \times 10$$^{23}$$ \text{ atoms/mol})$$

$$2.00 \times 6.022 \times 10$$^{23}$$ = 1.20 \times 10$$^{24}$$ atoms

Q: A student needs to convert 25.0 cm to inches. Given $$1 \text{ inch} = 2.54 \text{ cm}$$, what is the correct calculation?

$$25.0 \text{ cm} \times \frac{1 \text{ inch}}{2.54 \text{ cm}}$$

Question 1

Which of the following best describes a chemical change?

Accepted Answer

Iron rusting in the presence of oxygen

Question 2

A sample of pure water is decomposed into 16.0 g of oxygen and 2.0 g of hydrogen. What is the mass ratio of oxygen to hydrogen in water?

Accepted Answer

$$\frac{16.0}{2.0} = 8.0$$

Question 3

Which of the following statements is consistent with the law of conservation of mass?

Accepted Answer

The total mass before and after a chemical reaction remains the same.

Question 4

Which of the following is a derived SI unit?

Accepted Answer

Newton ($$N)$$

Question 5

A student measures the mass of a sample three times and gets values of 12.1 g, 12.2 g, and 12.1 g. The actual mass is 13.0 g. Which statement best describes the measurements?

Accepted Answer

The measurements are precise but not accurate.

Question 6

Which of the following best explains why gasoline is a good fuel for cars in terms of energy?

Accepted Answer

Gasoline has high potential energy stored in its chemical bonds, which is released as kinetic energy during combustion.

Question 7

Which of the following is NOT a correct statement about isotopes?

Accepted Answer

Isotopes of an element have different atomic numbers.

Question 8

A neutral atom of sodium ($$^{23}_{11}Na) $$has:

Accepted Answer

11 protons, 12 neutrons, 11 electrons

Question 9

Which experiment led to the discovery of the electron's charge?

Accepted Answer

Millikan's oil drop experiment

Question 10

Which of the following best describes the difference between a cation and an anion?

Accepted Answer

A cation has more protons than electrons; an anion has more electrons than protons.

Question 11

Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

Accepted Answer

$$	ext{Average mass} = (	ext{fraction}_1 	imes 	ext{mass}_1) + (	ext{fraction}_2 	imes 	ext{mass}_2)$$

Question 12

How many atoms are present in 2.00 mol of copper ($$Cu$$)? ($$N_A = 6.022 	imes 10$$^{23}$$ 	ext{ atoms/mol})$$

Accepted Answer

$$2.00 	imes 6.022 	imes 10$$^{23}$$ = 1.20 	imes 10$$^{24}$$ atoms

Question 13

Which of the following elements is most likely to form a cation?

Accepted Answer

Sodium ($$Na)$$

Question 14

Which scientist's work led to the conclusion that the atom is mostly empty space with a small, dense, positively charged nucleus?

Accepted Answer

Ernest Rutherford

Question 15

Which of the following is a physical property?

Accepted Answer

Melting point

Question 16

A student needs to convert 25.0 cm to inches. Given $$1 	ext{ inch} = 2.54 	ext{ cm}$$, what is the correct calculation?

Accepted Answer

$$25.0 	ext{ cm} 	imes \frac{1 	ext{ inch}}{2.54 	ext{ cm}}$$

Question 17

Which of the following best describes the periodic law?

Accepted Answer

When elements are arranged by increasing atomic number, their properties recur periodically.

Question 18

Which group of elements is characterized by being very unreactive and existing as gases at room temperature?

Accepted Answer

Noble gases

Question 19

A sample contains $$3.00 	imes 10$$^{24}$$ atoms of aluminum. How many moles of aluminum are present? (N_A = 6.022$$ 	imes $$10^{23}$$ 	ext{ atoms/mol}$$)

Accepted Answer

$$3.00 	imes 10$$^{24}$$ \div 6.022 	imes 10$$^{23}$$ = 4.98$$ mol

Measurement, Physical and Chemical Change: Foundations of General Chemistry

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