6. The atomic number of the element scandium is 21 and the mass number of its only isotope is 45.
(a) What is the number of electrons in a scandium ion, Sc+?
(1)
A 20
B 21
C 22
D 23
ANSWER
A 20
Analysis of Option/Explanation
Remember for a neutral charge atom, number of proton = number of electron. Therefore, in case of Sc, the electron number is 21. But for Sc+, it reflects that one electron has been removed therefore it will have “number of electron = 20”. Hence, Option A is the correct answer.
(b) In a mass spectrometer, scandium forms Sc+ and Sc2+ ions.
What is the m/z value for the mass spectrum peak due to the Sc2+ ions?
(1)
A 22.5
B 33.0
C 45.0
D 90.0
ANSWER
A 22.5
Analysis of Option/Explanation
The m/z value for Sc2+ is calculated as =
Hence, m/z = 22.5. Therefore, option A is the correct answer.
