Q: Which equation correctly calculates the relative atomic mass ($$A_r) of an $$element with two isotopes, $$a$$ and $$b$$?

$$A_r = \frac{(%a \times A_{a}) + (%b \times A_{b})}{100}$$

Question 1

Which statement best describes isotopes of an element?

Accepted Answer

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

Question 2

Lithium has two naturally occurring isotopes: lithium-6 and lithium-7. Which property will be the same for both isotopes?

Accepted Answer

Chemical reactivity

Question 3

Why is the unified atomic mass unit ($$u) $$defined as one twelfth the mass of a carbon-12 atom?

Accepted Answer

To provide a standard reference for atomic masses that is easy to reproduce.

Question 4

A sample of thallium contains two isotopes: $$^{203}	ext{Tl} (29.50$$%) and $$^{205}	ext{Tl} (70.50$$%). What is the relative atomic mass of thallium in this sample?

Accepted Answer

$$203.6$$

Question 5

Copper has two isotopes: copper-63 (69.17%) and copper-65 (30.83%). Calculate the relative atomic mass of copper.

Accepted Answer

$$63.62$$

Question 6

Which equation correctly calculates the relative atomic mass ($$A_r) of an $$element with two isotopes, $$a$$ and $$b$$?

Accepted Answer

$$A_r = \frac{(%a 	imes A_{a}) + (%b 	imes A_{b})}{100}$$

Question 7

Vanadium has two naturally occurring isotopes: vanadium-50 and vanadium-51. The atomic mass of vanadium is $$50.94. $$Which isotope is more abundant and why?

Accepted Answer

Vanadium-51, because the atomic mass is closer to 51.

Question 8

Which of the following best explains why isotopes of chlorine ($$^{35}	ext{Cl}$$ and $$^{37}	ext{Cl}) $$have different physical properties but similar chemical properties?

Accepted Answer

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

Question 9

A titanium atom has the same mass as four carbon atoms. What is the relative atomic mass of titanium?

Accepted Answer

$$48$$

Question 10

If three helium atoms have the same mass as one carbon atom, what is the relative atomic mass of helium?

Accepted Answer

$$4$$

Question 11

Which of the following is NOT a reason why relative atomic mass is used instead of grams to compare atoms?

Accepted Answer

Relative atomic mass is always a whole number.

Question 12

A natural sample of chlorine contains 75.77% $$^{35}	ext{Cl} ($$atomic mass 34.969) and 24.23% $$^{37}	ext{Cl} ($$atomic mass 36.966). What is the relative atomic mass of chlorine?

Accepted Answer

$$35.45$$

Question 13

Which of the following statements about isotopes is FALSE?

Accepted Answer

Isotopes of an element always have the same physical properties.

Question 14

A hospital uses a radioactive isotope of iodine for thyroid scans. Why is the chemical reactivity of this isotope the same as non-radioactive iodine?

Accepted Answer

Because both have the same number of protons and electrons.

Question 15

Which of the following best describes the physical property difference between $$^{6}	ext{Li}$$ and $$^{7}	ext{Li}$$?

Accepted Answer

They have different mass and density.

Question 16

A scientist discovers a new element with two isotopes: 40% isotope A (mass 100) and 60% isotope B (mass 105). What is the relative atomic mass of the element?

Accepted Answer

$$103$$

Question 17

Which of the following is the best definition of 'relative atomic mass'?

Accepted Answer

The mass of an atom compared to one twelfth the mass of a carbon-12 atom.

Question 18

Which real-world application relies on the concept of isotopes having different masses but identical chemical properties?

Accepted Answer

Using uranium-235 and uranium-238 in nuclear reactors.

Question 19

A forensic scientist analyzes a sample and finds the ratio of $$^{13}	ext{C} to$$ $$^{12}	ext{C} is $$higher than normal. What could this indicate?

Accepted Answer

The sample is enriched in $$^{13}	ext{C}$$, possibly from a biological or synthetic process.

Question 20

Which calculation would you use to determine the relative atomic mass of an element with three isotopes: 20% at mass 10, 50% at mass 11, and 30% at mass 12?

Accepted Answer

$$A_r = \frac{(20 	imes 10) + (50 	imes 11) + (30 	imes 12)}{100}$$

Isotopes and Relative Atomic Mass: Study Notes

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