3.1.1.2 Mass number and isotopes

A student has a 10 cm³ sample of 1.00 × 10^–2 mol dm^–3 methanoic acid solution. The student is asked to dilute the methanoic acid solution to a concentration of 2.00 × 10^–4 mol dm^–3 by adding distilled water.

Which volume of water should be added?

• 200 cm³

• 490 cm³

• 500 cm³

• 510 cm³

Which statement about time of flight mass spectrometry is correct?

• The current in the detector is proportional to the ion abundance

• Sample particles gain electrons to form positive ions

• Particles are detected in the order of their kinetic energies

• Ions are accelerated by a magnetic field

Chlorine exists as two isotopes ³⁵Cl and ³⁷Cl in the ratio 3:1

Which statement about peaks in the mass spectrum of Cl₂ is correct?

• Peaks at m/z = 70 and 74 in the ratio 3:1

• Peaks at m/z = 70, 72 and 74 in the ratio 9:6:1

• Peaks at m/z = 70, 72 and 74 in the ratio 9:3:1

• Peaks at m/z = 70 and 72 in the ratio 3:1

Bromine exists as two isotopes ⁷⁹Br and ⁸¹Br, which are found in almost equal abundance.

Which of the statements is correct?

• The first ionisation energy of ⁷⁹Br is less than the first ionisation energy of ⁸¹Br

• The atomic radius of ⁷⁹Br is less than the atomic radius of ⁸¹Br

• The mass spectrum of C₃H₇Br has two molecular ion peaks at 122 and 124

• ⁷⁹Br is more reactive than ⁸¹Br

Which of these atoms has the smallest number of neutrons?

• ³H

• ⁴He

• ⁵He

• ⁴Li

Ions of two isotopes of iron are

⁵³Fe^{2+ 56}Fe²⁺

Which statement is correct?

• The ions of both the isotopes have the electronic configuration 1s²2s²2p⁶3s²3p⁶4s²3d⁶

• The ions of both the isotopes contains 26 neutrons

• ⁵³Fe²⁺ has fewer protons than ⁵⁶Fe²⁺

• After acceleration to the same kinetic energy ⁵⁶Fe²⁺ will move more slowly than ⁵³Fe²⁺

The successive ionisation energies for element X are shown in the graph. Which element is X?

• Nitrogen

• Phosphorus

• Aluminium

• Boron

Chlorine has two isotopes, ³⁵Cl and ³⁷Cl. The number of molecular ion peaks in the mass spectrum of a sample of Cl₂ is

• 2

• 3

• 4

• 5

Assuming that chlorine exists as two isotopes, and that hydrogen and carbon exist as one isotope each, how many molecular ion peaks will be shown in the mass spectrum of C₄H₆Cl₄?

• 2

• 3

• 4

• 5