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 .

EASY

AS and A Level

IMPORTANT

Earn 100

What is the volume of carbon dioxide produced when $14 g$ of ethene, $C_{2} H_{4}$ , reacts with excess oxygen? ( $M_{r}$ ethene $= 28$ ).

$C_{2} H_{4} (g) + 3 O_{2} (g) \to 2 {CO}_{2} (g) + 2 H_{2} O (l)$ .

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Important Questions on Atoms, Molecules and Stoichiometry

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 1

State the meaning of the term relative atomic mass.

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 1

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.

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 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.

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 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: $Fe = 55.8, B = 10.8, O = 16.0$ ).

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 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.

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

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

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

What is meant by the term hydrated salt?

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

A particular isotope of hafnium has

72

protons and a nucleon number of

180

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

What is the volume of carbon dioxide produced when 14 g of ethene, C2H4, reacts with excess oxygen? (Mr ethene=28). C2H4g+3O2g→2CO2g+2H2Ol.

Important Questions on Atoms, Molecules and Stoichiometry

Learn and Prepare for any exam you want !

What is the volume of carbon dioxide produced when $14 g$ of ethene, $C_{2} H_{4}$ , reacts with excess oxygen? ( $M_{r}$ ethene $= 28$ ).

$C_{2} H_{4} (g) + 3 O_{2} (g) \to 2 {CO}_{2} (g) + 2 H_{2} O (l)$ .