I wasgiven this solution when I asked a question, but I do notcompletely underst

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I wasgiven this solution when I asked a question, but I do notcompletely understand the solution. Can someone explain how to dothe part of the question that I highlighted?

Question Details: Can someone explain in detail how to do this problem? A 0.356-g sample of XH2(s) reacts with wateraccording to the following equation: The hydrogen evolved is collected over water at23oC and occupies a volume of 431 mL at 746 mmHg totalpressure. Find the number of moles of H2 produced andthe atomic mass of X. Vapor pressure of H2O = 21mmHg. To solve this problem first we have to calculate the number ofmoles of the H2 obtained in the reaction. We know that the ideal gas equation is   PV =nRT Where P- pressure of the hydrgogen = 746 mmHg-21mmHg =725 mmHg = 0.9539 atm            V - volume of the gas = 421 mL = 0.431L            T = absolute temaparature = 23+273 = 296K Therefore number of moles of the gas obtained =PV/RT                                                                        = 0.9539 atm*0.431L/0.08206Latm/mol.K*296K                                                                        = 0.01692 mole According to given stoichiometric equation we have the0.01692/2 mole of XH2 Thus thenumber of moles of hydrogen present = 0.00846moles But the mass ofXH2 present initially = 0.356g Hence  0.00846 mole = 0.356g/M.Wt of XH2       M.Wt of XH2       =42g/mole Therefore molarmass of X =42g/mole - 2g/mole                                           = 40g/mole This relates the molar mass of 'a' Therefore given compound is  CaH2       M.Wt of XH2       =42g/mole Therefore molarmass of X =42g/mole - 2g/mole                                           = 40g/mole This relates the molar mass of 'a' Therefore given compound is  CaH2 I wasgiven this solution when I asked a question, but I do notcompletely understand the solution. Can someone explain how to dothe part of the question that I highlighted?

Question Details: Can someone explain in detail how to do this problem? A 0.356-g sample of XH2(s) reacts with wateraccording to the following equation: XH2(s) + 2H2O(l) X(OH)2(s)+ 2H2 (g) The hydrogen evolved is collected over water at23oC and occupies a volume of 431 mL at 746 mmHg totalpressure. Find the number of moles of H2 produced andthe atomic mass of X. Vapor pressure of H2O = 21mmHg. I wasgiven this solution when I asked a question, but I do notcompletely understand the solution. Can someone explain how to dothe part of the question that I highlighted? Question Details: Can someone explain in detail how to do this problem? A 0.356-g sample of XH2(s) reacts with wateraccording to the following equation: XH2(s) + 2H2O(l) X(OH)2(s)+ 2H2 (g) The hydrogen evolved is collected over water at23oC and occupies a volume of 431 mL at 746 mmHg totalpressure. Find the number of moles of H2 produced andthe atomic mass of X. Vapor pressure of H2O = 21mmHg. To solve this problem first we have to calculate the number ofmoles of the H2 obtained in the reaction. We know that the ideal gas equation is PV =nRT Where P- pressure of the hydrgogen = 746 mmHg-21mmHg =725 mmHg = 0.9539 atm V - volume of the gas = 421 mL = 0.431L T = absolute temaparature = 23+273 = 296K Therefore number of moles of the gas obtained =PV/RT = 0.9539 atm*0.431L/0.08206Latm/mol.K*296K = 0.01692 mole According to given stoichiometric equation we have the0.01692/2 mole of XH2 Thus thenumber of moles of hydrogen present = 0.00846moles But the mass ofXH2 present initially = 0.356g Hence 0.00846 mole = 0.356g/M.Wt of XH2 M.Wt of XH2 =42g/mole Therefore molarmass of X =42g/mole - 2g/mole = 40g/mole This relates the molar mass of 'a' Therefore given compound is CaH2

Explanation / Answer

According to the reaction, 1 mol XH2 produces 2 molH2            => to find how many mole of XH2 need, you take moleof H2 is already found divides by 2(you get the number0.00846)            And they give the mass of XH2=> find the molar massof it. M = m/n = 42g/mol                  The compound has formula XH2(notice there is 2H incompound)                                                The molar mass of it is : X + 2 = 42                                                        FInd the X => X = 40                   Look at the periodic table, X is Ca Hope it helps

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