ATOMS, MOLECULES AND STOICHIOMETRY

What is the molar mass of C₂H₄O₂?

[Relative atomic mass C=12, H=1, O=16]

• 40 g/mol

• 50 g/mol

• 60 g/mol

• 68 g/mol

FILL IN THE BLANK

Isotopes are atoms that have the same number of .....

but different numbers of ...............

• protons/ electrons

• protons/ neutrons

• neutrons/ protons

• neutrons/ electrons

Relative Molecular Mass is defined as the:

• Average mass of one molecule of any substance compared to 1/12 the mass of one atom of C – 12

• Average mass of one atom of any substance compared to 1/12 the mass of one atom of C – 12

• The mass of one mole of substance in gram

• none of these

Which of the following species will be deflected most in a mass spectrometer?

• ³⁶Y⁺

• ³⁶Y²⁺

• ³⁸Y⁺

• ³⁸Y²⁺

The compound NCl₃ is formed from ¹⁴N , ³⁵Cl and ³⁷Cl isotopes. The relative abundance of ³⁵Cl to ³⁷Cl is 3:1. Which statement about the mass spectrum of NCl₃ is true?

• The base peak corresponds to N⁺ ion

• The m/e value for the last peak is 123

• The number of peaks for NCl₃⁺ ion is 4

• The relative abundance of N³⁵Cl₃⁺ ion to N³⁷Cl₃⁺ ion is 3:1

A mixture of 8.0 g of a monoatomic gas G and an unknown quantity of diatomic gas J has a volume of V m³ at stp. When 20.0 g of gas G is added to the mixture, under the same conditions, the volume of the mixture is 2V m³. Calculate the quantity of gas J in the mixture.

[ RAM : G = 4, J =1 . Assuming that gas G does not react with gas J ]

• 2 g

• 3 g

• 5 g

• 6 g

An element X with a relative atomic mass of 28.1 consists of isotopes ²⁸X, ²⁹X and ³⁰X.

If the percentage abundance of ²⁹X and ³⁰X are the same what is the percentage abundance of ²⁸X?

• 0.32

• 3.33

• 93.3

• 96.7

Chlorine consists of two isotopes; ³⁵Cl and ³⁷Cl in the ratio 3:1.

Phosphorous is monoisotopic, ³¹P. A sample of phosphorous trichloride, PCl₂, is analysed in the mass spectrometer. Part of the mass spectrum consists of three lines with m/e of 101, 103 and 105. Which of the following diagram best represent the relative abundance of the three lines?

²⁸ ₁₄ Si and ³⁰ ₁₄ Si are two isotopes of silicon. The relative atomic mass of Si is 28.1. Which statement is true about these isotopes?

• ²⁸ ₁₄ Si is smaller than ³⁰ ₁₄ Si .

• ²⁸ ₁₄ Si and ³⁰ ₁₄ Si are radioactive .

• ²⁸ ₁₄ Si is more abundant than ³⁰ ₁₄ Si .

• The total number of sub-atomic particles in ²⁸ ₁₄ Si and ³⁰ ₁₄ Si is the same.

The mass spectrum of an element is shown below.

Which statement is true about the element?

• The element has two isotopes.

• Peak X is due to a dipositive ion.

• The element is a diatomic molecule.

• The relative atomic mass of the element is 38.