Question
6 Use the periodic table to work out which of these compounds has a relative formula mass of 100. CaCl_(2) H_(2)SO_(4) MgCO_(3) CaCO_(3)
Answer
4.5
(197 Votes)
Kieran
Elite · Tutor for 8 years
Answer
D
Explanation
First step to solve this problem requires knowledge of atomic masses of the elements which belong to respective compounds. The atomic mass usually, can be discovered using a periodic table. The relative formula mass (M_r) of a compound is the sum total of the atomic masses of each atom in its formula. Therefore, we need to calculate the formula mass of all four compounds (✓Chloroform - Plastic white (CaCl2), Sulfuric acid (H2SO4), Magnesium carbonate (MgCO3), and Calcium carbonate (CaCO3)) and to check which one has formula mass equal to 100. Atomic masses approximated to nearest whole number:Calcium (Ca): 40Chlorine (Cl): 35.5 Hydrogen (H):1Sulphur(S) - 32Oxygen (O) - 16Magnesium (Mg) - 24 andCarbon (C) - 12Let's calculate the molecular masses of each of them. The mass of 𝐶𝑎𝐶𝑙2 = (1 x Mass of Ca) + (2 x Mass of Cl) = 40 + 2(35.5) =111 The mass of H2SO4 = (2 x mass of
) + (1 x mass of
) + (4 x mass of
) =2+(1x32)+4(16)=98 The total mass of MgCO3 =(1 x mass of
) + (1 x mass of
) + (3 x mass of
) = 24+12+3*(16)=84 (Not '100')𝐶𝑎CO3's total mass = (1 x mass of Ca )+(1x This mass of
) + This mass of 3x\(O) about nutrition = 40+12+3*(16)=100 which is what we have been looking for.