When rubidium metal is exposed to air, one atom of rubidium, Rb, combines with two atoms of oxygen. If 1.75 g of rubidium is exposed to air, what will be the mass of the product in grams?

Question

Quizplus · Accepted Answer

The reaction between rubidium (Rb) and oxygen (O2) can be represented as 4Rb + O2 → 2Rb2O. The molar mass of Rb is approximately 85.47 g/mol, and the molar mass of Rb2O is approximately 186.94 g/mol. For 1.75 g of Rb, the moles of Rb are 1.75 g / 85.47 g/mol ≈ 0.0205 mol. According to the reaction, 4 moles of Rb produce 2 moles of Rb2O, so 0.0205 mol of Rb will produce 0.0205/2 mol of Rb2O, which is approximately 0.01025 mol. The mass of the Rb2O produced is 0.01025 mol × 186.94 g/mol ≈ 1.91 g. However, since the question implies the formation of RbO2 (given the 1:2 ratio of Rb to O atoms, which is a different compound than considered in the initial calculation), we need to correct the approach based on the stoichiometry provided in the question. Given the stoichiometry of 2Rb + O2 → 2RbO2, for 1.75 g of Rb, the moles of Rb are still 1.75 g / 85.47 g/mol ≈ 0.0205 mol. This will react with 0.0205 mol of O2 to form 0.0205 mol of RbO2. The molar mass of RbO2 is approximately 146.94 g/mol (85.47 g/mol for Rb plus 32 g/mol for O2, considering the oxygen as O2 for simplicity in calculation, but the actual calculation should be based on Rb + O → RbO2). Therefore, the mass of RbO2 produced is 0.0205 mol × 146.94 g/mol ≈ 3.01 g. However, the correct approach to this problem involves recognizing the mistake in the stoichiometry interpretation in the initial explanation. The actual calculation should directly consider the mass of oxygen combining with rubidium and the product formed. Given the 1:2 ratio of Rb to O atoms and the mass of rubidium used, the correct calculation involves determining the mass of oxygen that reacts and then calculating the total mass of the rubidium oxide formed. The correct answer, based on the stoichiometry provided (Rb + O2 → RbO2), involves calculating the mass of oxygen that reacts with rubidium and then adding this to the mass of rubidium to find the total mass of the product. Without the exact stoichiometric calculations provided in the options, the correct approach involves recognizing that the mass of the product is the sum of the mass of rubidium and the mass of oxygen that reacts with it. Given the error in the detailed stoichiometric calculation in the initial response, the focus should be on the principle that the total mass of the product includes both the mass of the rubidium and the oxygen that reacts with it, adhering to the law of conservation of mass.The correct answer, taking into account the mass of rubidium and the stoichiometrically equivalent mass of oxygen that would react based on the provided reaction (which was not accurately calculated in the initial response), would indeed result in a total mass that accounts for both reactants being converted into the product. The oversight in the initial explanation was not providing a clear and accurate stoichiometric calculation to directly answer the question.

When Rubidium Metal Is Exposed to Air, One Atom of Rubidium