Question
The relative atomic mass of chlorine is 35.5 .
When calculating relative atomic mass, which particle is the mass of a chlorine atom compared to?
A a neutron
B a proton
C an atom of carbon-12
D an atom of hydrogen-1
▶️Answer/Explanation
Ans:C
When calculating the relative atomic mass, the mass of a chlorine atom is compared to the mass of a carbon-12 atom. The relative atomic mass of an element is determined by comparing the average mass of its atoms to the mass of a carbon-12 atom, which is defined as exactly 12 atomic mass units (amu).
Question
What is the relative formula mass of magnesium nitrate, \(Mg(NO_3)_2\)?
A 74 B 86 C 134 D 148
▶️Answer/Explanation
Ans: D
The relative formula mass of a molecule is the sum of the atomic masses of all the atoms in its chemical formula. It is also known as the molecular mass or molecular weight.
The relative formula mass of magnesium nitrate, \(Mg(NO_3)_2\) = 24 + 2*14+6*16 = 148.
Question
A compound has the formula \(XF_2\) and has a relative mass of 70.
What is element X?
A gallium
B germanium
C sulfur
D ytterbium
▶️Answer/Explanation
Ans: C
F has relative mass of 19.
\(XF_2\) has a relative mass of 70.
X+2*19=70
X=32. X is Sulfur.
Question
The compound magnesium nitrate has the formula \(Mg(NO_{3})_{2}\). What is the relative formula mass of magnesium nitrate?
A. 86 B. 134 C. 148 D. 172
▶️Answer/Explanation
Ans:
C
The relative formula mass of a molecule is the sum of the atomic masses of all the atoms in its chemical formula. It is also known as the molecular mass or molecular weight.
The relative formula mass of magnesium nitrate, \(Mg(NO_3)_2\) = 24 + 2*14+6*16 = 148.
Question
The relative formula mass, Mr, of calcium carbonate, CaCO3, is 100.
What is the mass of carbon present in 100 g of calcium carbonate?
A 12 g B 36 g C 40 g D 60 g
▶️Answer/Explanation
Ans:
A
The relative formula mass, Mr, of calcium carbonate, CaCO3, is 100.
Mass of carbon present in 100 g of calcium carbonate is mass of 1 mole C atom = 12g.