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

$$\text{Atomic mass} = (\text{mass of isotope 1} \times \%\text{abundance of isotope 1}) + (\text{mass of isotope 2} \times \%\text{abundance of isotope 2})$$

Question 1

Which of the following statements best distinguishes a chemical change from a physical change?

Accepted Answer

A chemical change results in the formation of new substances with different chemical properties.

Question 2

Which of the following is a correct interpretation of the chemical formula $$\mathrm{C_6H_{12}O_6$}$$?

Accepted Answer

It contains 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms per molecule.

Question 3

A student measures the mass of a sample as $$12.30 g $$and its volume as $$4.1 mL. $$What is the density of the sample, reported with the correct number of significant figures?

Accepted Answer

$$3.0\ \mathrm{g/mL}$$

Question 4

Which of the following is a heterogeneous mixture?

Accepted Answer

Salad dressing with oil and vinegar

Question 5

Which of the following is the correct metric unit for measuring temperature?

Accepted Answer

Kelvin ($$K)$$

Question 6

Convert $$25.0\ ^\circ\mathrm{C} to $$Kelvin.

Accepted Answer

$$298.2\ K$$

Question 7

Which of the following is NOT a sign that a chemical reaction has occurred?

Accepted Answer

A solid melts into a liquid.

Question 8

How many significant figures are in the measurement $$0.00450 g$$?

Accepted Answer

3

Question 9

Which of the following best describes the difference between qualitative and quantitative measurements?

Accepted Answer

Qualitative measurements describe characteristics without numbers; quantitative measurements use numbers.

Question 10

A sample of water is heated from $$20.0\ ^\circ\mathrm{C} to$$ $$85.0\ ^\circ\mathrm{C}. If $$the mass of water is $$50.0 g$$, how much heat ($$q) is $$absorbed? (Specific heat of water $$= 4.184\ \mathrm{J/g\ ^\circ C})$$

Accepted Answer

$$13,600\ \mathrm{J}$$

Question 11

Which of the following correctly lists the sublevels in order of increasing energy within a shell?

Accepted Answer

$$s \u003c p \u003c d \u003c f$$

Question 12

What is the electron configuration for a neutral atom of oxygen ($$Z=8$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^4$$

Question 13

Which of the following statements about atomic orbitals is correct?

Accepted Answer

Each orbital can hold a maximum of 2 electrons.

Question 14

A neutral atom of sodium ($$Z=11) $$has how many protons, neutrons, and electrons? (Assume mass number $$=23)$$

Accepted Answer

11 protons, 12 neutrons, 11 electrons

Question 15

Which of the following is the correct noble gas shorthand electron configuration for calcium ($$Z=20$$)?

Accepted Answer

$$[Ar]\ 4s^2$

Question 16

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

Accepted Answer

A mixture can be separated by physical means, while a compound requires chemical means.

Question 17

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

Accepted Answer

$$	ext{Atomic mass} = (	ext{mass of isotope 1} 	imes \%	ext{abundance of isotope 1}) + (	ext{mass of isotope 2} 	imes \%	ext{abundance of isotope 2})$$

Question 18

Which of the following is the correct order of filling for atomic orbitals according to the Aufbau principle?

Accepted Answer

$$1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d$$

Question 19

Which of the following best describes the relationship between valence electrons and chemical reactivity?

Accepted Answer

Elements with similar numbers of valence electrons have similar chemical reactivity.

Question 20

A student needs to convert $$5.00$$ meters to centimeters using dimensional analysis. Which of the following is the correct setup and answer?

Accepted Answer

$$5.00\ \mathrm{m} 	imes \frac{100\ \mathrm{cm}}{1\ \mathrm{m}} = 500\ \mathrm{cm}$$

GOB Chemistry Study Guide: Matter, Measurement, and the Periodic Table

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