A sample of boron was found to have the following % composition by mass: B 5 10 18 . 7 % , B 5 11 81 . 3 % . Calculate a value for the relative atomic mass of boron. Give your answer to 3 significant figures.

Relative atomic mass is defined as the ratio of the average mass of atoms of a chemical element in a given sample to the atomic mass constant. The atomic mass constant is defined as being 1 12 of the mass of a carbon - 12 atom. Relative atomic mass = The sum of products of isotopic masses with their percentages of an element 100 Then, the relative atomic mass of boron = 10 . 0 × 18 . 7 + 11 . 0 × 81 . 3 100 = 10 . 813 amu .

A sample of boron was found to have the following % composition by mass: B 5 10 18 . 7 % , B 5 11 81 . 3 % . Calculate a value for the relative atomic mass of boron. Give your answer to 3 significant figures.

Relative atomic mass is defined as the ratio of the average mass of atoms of a chemical element in a given sample to the atomic mass constant. The atomic mass constant is defined as being 1 12 of the mass of a carbon - 12 atom. Relative atomic mass = The sum of products of isotopic masses with their percentages of an element 100 Then, the relative atomic mass of boron = 10 . 0 × 18 . 7 + 11 . 0 × 81 . 3 100 = 10 . 813 amu .

The mass spectrum of zirconium is shown below. Give the isotopic symbol for the most abundant isotope of zirconium.

Isotopes are defined as one of two or more chemical species of atoms of an element with the same atomic number but with different atomic masses due to the presence different neutron numbers. Zirconium has five naturally occurring isotopes. 90 Zr , 91 Zr , 92 Zr , 94 Zr and 96 Zr (the longest-lived radioisotope of zirconium). Zr 40 90 is the most common, making up 51 . 50 % of all zirconium.

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AS and A Level

IMPORTANT

Earn 100

A sample of boron was found to have the following $%$ composition by mass: ${}_{5}^{10}B (18.7 %)$ , ${}_{5}^{11}B (81.3 %)$ . Calculate a value for the relative atomic mass of boron. Give your answer to $3$ significant figures.

Important Questions on Atoms, Molecules and Stoichiometry

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AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 3 - Atoms, Molecules and Stoichiometry>EXAM-STYLE QUESTIONS>Q 1

Boron ions,

B^{3 +}

, can be formed by bombarding gaseous boron with high-energy electrons. Deduce the number of electrons in one

B^{3 +}

ion.

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AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 3 - Atoms, Molecules and Stoichiometry>EXAM-STYLE QUESTIONS>Q 1

Boron is present in compounds called borates. Use the $A_{r}$ values below to calculate the relative molecular mass of iron(III) borate, $Fe {({BO}_{2})}_{3}$ .

( $A_{r}$ values: $Fe = 55.8, B = 10.8, O = 16.0$ ).

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AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 3 - Atoms, Molecules and Stoichiometry>EXAM-STYLE QUESTIONS>Q 1

Boron is present in compounds called borates. The accurate relative atomic mass of iron, $Fe$ , is $55.8$ . Explain why the accurate relative atomic mass is not a whole number.

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AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 3 - Atoms, Molecules and Stoichiometry>EXAM-STYLE QUESTIONS>Q 2

This question is about some metals and metal compounds. Hafnium,

Hf

, forms a hydrated peroxide whose formula can be written as

{HfO}_{3} . 2 H_{2} O

. Use the

A_{r}

values below to calculate the relative molecular mass of hydrated hafnium peroxide. (

A_{r}

values:

Hf = 178.5, H = 1.0, O = 16.0

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AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 3 - Atoms, Molecules and Stoichiometry>EXAM-STYLE QUESTIONS>Q 2

What is meant by the term hydrated salt?

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AS and A Level

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Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 3 - Atoms, Molecules and Stoichiometry>EXAM-STYLE QUESTIONS>Q 2

A particular isotope of hafnium has

72

protons and a nucleon number of

180

. Write the isotopic symbol for this isotope, showing this information.

EASY

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 3 - Atoms, Molecules and Stoichiometry>EXAM-STYLE QUESTIONS>Q 2

The mass spectrum of zirconium is shown below.

Question Image

Give the isotopic symbol for the most abundant isotope of zirconium.

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AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 3 - Atoms, Molecules and Stoichiometry>EXAM-STYLE QUESTIONS>Q 2

The mass spectrum of zirconium is shown below.

Question Image

Use the information from this mass spectrum to calculate the relative atomic mass of zirconium. Give your answer to $3$ significant figures.

A sample of boron was found to have the following % composition by mass: B51018.7%, B51181.3%. Calculate a value for the relative atomic mass of boron. Give your answer to 3 significant figures.

Important Questions on Atoms, Molecules and Stoichiometry

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A sample of boron was found to have the following $%$ composition by mass: ${}_{5}^{10}B (18.7 %)$ , ${}_{5}^{11}B (81.3 %)$ . Calculate a value for the relative atomic mass of boron. Give your answer to $3$ significant figures.