Passage
The alkaline-earth metals are a highly reactive family of metals occupying Group 2 (IIA) of the periodic table. In their elemental form, the alkaline-earth metals have a shiny, silvery-white to slightly yellowish appearance. The alkaline-earth metals exhibit some similarities to the chemistry of the alkali metals (Group 1) but are a little less reactive.Atoms of the alkaline-earth metals (M) have only two valence electrons and a low first and second ionization energy. Consequently, these metals readily lose both electrons to produce cations with a +2 charge (M +2 ) during reactions with nonmetals. As a result, the alkaline-earth metals do not exist in their elemental metallic form in nature. Instead, the Group 2 elements are found primarily as metal oxides, which form by reacting oxygen (Reaction 1).

Similarly, elemental samples of alkaline-earth metals will react with elemental halogens (X 2 ) to form metal halides (Reaction 2), all of which are ionic except for BeCl 2 .

Except for beryllium, the alkaline-earth metals react with water to produce very basic metal hydroxide solutions and hydrogen gas (Reaction 3).

The most difficult alkaline-earth metal to study is radium, because it is a rare radioactive element that is produced from the nuclear decay of uranium. The most common natural isotope, radium-226, has a half-life of 1,600 years and decays by alpha emission into radon-222 (Reaction 4).

-What is the mass of water necessary to generate 11.2 L of hydrogen gas if calcium metal reacts with water at standard temperature and pressure (STP)?

Question

Passage
The alkaline-earth metals are a highly reactive family of metals occupying Group 2 (IIA) of the periodic table.  In their elemental form, the alkaline-earth metals have a shiny, silvery-white to slightly yellowish appearance.  The alkaline-earth metals exhibit some similarities to the chemistry of the alkali metals (Group 1) but are a little less reactive.Atoms of the alkaline-earth metals (M) have only two valence electrons and a low first and second ionization energy.  Consequently, these metals readily lose both electrons to produce cations with a +2 charge (M +2 ) during reactions with nonmetals.  As a result, the alkaline-earth metals do not exist in their elemental metallic form in nature.  Instead, the Group 2 elements are found primarily as metal oxides, which form by reacting oxygen (Reaction 1).
  
Similarly, elemental samples of alkaline-earth metals will react with elemental halogens (X 2 ) to form metal halides (Reaction 2), all of which are ionic except for BeCl 2 .
  
Except for beryllium, the alkaline-earth metals react with water to produce very basic metal hydroxide solutions and hydrogen gas (Reaction 3).
  
The most difficult alkaline-earth metal to study is radium, because it is a rare radioactive element that is produced from the nuclear decay of uranium.  The most common natural isotope, radium-226, has a half-life of 1,600 years and decays by alpha emission into radon-222 (Reaction 4).
 
-What is the mass of water necessary to generate 11.2 L of hydrogen gas if calcium metal reacts with water at standard temperature and pressure (STP)?

Quizplus · Accepted Answer

11ecba2d_11e5_56a8_a3bf_659fa71c134d_MD0008_00 Under conditions of standard temperature and pressure (STP), which are defined as 0°C (273.15 K) and 1 atm pressure, 1 mole of gas occupies a volume of 22.4 L. Using this relationship, the moles of a gas present in a given volume at STP can be determined. In a reaction, the moles of gas can be related to the moles of other chemical species by applying stoichiometric mole ratios obtained from a balanced reaction equation. The mass of a given number of moles of a particular compound can subsequently be found using its molar mass. If 11.2 L of H₂ gas are produced in the reaction of calcium metal with water (Reaction 3) at STP, the number of moles of H₂ gas produced in the reaction is given by: (11.2 L H₂) / (22.4 L/mol) = 0.500 mol H₂ According to the balanced equation, the molar ratio of H₂O to H₂ is 2:1. Using this ratio, the required number of moles of H₂O can be determined: (0.500 moles H₂) × (2 mol H₂O) / (1 mol H₂) = 1.00 mol H₂O The mass of the required moles of H₂O can be calculated using its molar mass: (1.00 mol H₂O) × (18.02 g/mol) = 18.02 g H₂O (Choice A) 2.0 g is obtained if the calculation is done using the molar mass of H₂ (2.02 g/mol) instead of H₂O (18.02 g/mol). (Choice B) 4.5 g is obtained if the 2:1 mole ratio of H₂O:H₂ is flipped and the calculation is divided by 2 instead of multiplied by 2. (Choice C) 9.0 g is obtained if a 1:1 mole ratio of H₂O:H₂ is used in the calculation instead of the correct 2:1 ratio. Educational objective: At standard temperature and pressure (STP), gases in reactions can be related to the molar volume of 22.4 L/mol. Mole ratios from balanced chemical reactions can be used to relate the moles of the gas to the moles of other reaction species. The mass of a given number of moles of a particular species can be found using its molar mass.