When rubidium metal is exposed to air,two atoms of rubidium,Rb,combine with one atom of oxygen.If 1.98 grams of rubidium is exposed to air,what will be the mass of the product in grams?
A)17.98 g
B)2.17 g
C)9.98 g
D)8.66 g
E)4.33 g

Question

Quizplus · Accepted Answer

The balanced chemical equation for the reaction between rubidium and oxygen is:
4Rb + O2 → 2Rb2O
This means that 4 atoms of rubidium react with 1 molecule of oxygen to form 2 formula units of rubidium oxide. 
We can use stoichiometry to find the amount of rubidium oxide produced when 1.98 grams of rubidium reacts:
1 mol Rb = 85.47 g Rb
1 mol Rb2O = 186.94 g Rb2O
Using the molar ratio from the balanced equation:
1 mol Rb : 1/2 mol Rb2O
85.47 g Rb : 93.47 g Rb2O
1.98 g Rb x (93.47 g Rb2O / 85.47 g Rb) = 2.17 g Rb2O
Therefore, the mass of the product in grams is 2.17 g, which corresponds to choice (B).

When Rubidium Metal Is Exposed to Air,two Atoms of Rubidium,Rb,combine