Question

К 360 г раствора сульфата аммония добавили избыток щелочи, полученный раствор нагрели до прекращения выделения газа. Общий объем газа составил 13,44 л (н. у. ) определите массовую долю сульфата аммония в растворе. Почему в решении проверенному экспертом, не учитывается масса выделившегося газа, разве масса раствора не стала меньше?

Answer 1

Ответ:

m(р-ра NH4)2SO4) = 360 г

+NaOH

V(NH3) = 13,44 л

Найти:

ω((NH4)2SO4)=?

Vm = 22,4 л/моль

n(NH3) = 13,44 л/22,4 л/моль = 0,6 моль

M((NH4)2SO4) = 132 г/моль

(NH4)2SO4 + 2NaOH = Na2SO4 + 2NH3↑ + 2H2O

Из УХР следует, что n((NH4)2SO4) = 0,5n(NH3)

n((NH4)2SO4) = 0,5*0,6 моль = 0,3 моль

m((NH4)2SO4) = 0.3 моль*132 г/моль = 39,6 г

ω((NH4)2SO4) = 39.6 г/360 г =  0,11 или 11%

Ответ: 11%

Answer 2

Calculation of the Mass Fraction of Ammonium Sulfate in the Solution

To determine the mass fraction of ammonium sulfate in the solution, we need to consider the chemical reaction that occurred when excess alkali was added to the ammonium sulfate solution. The reaction can be represented as follows:

2NH4+ + SO4^2- + 2OH- → (NH4)2SO4 + 2H2O

From the balanced equation, we can see that 2 moles of ammonium sulfate are formed for every 2 moles of hydroxide ions (OH-) consumed. Therefore, the moles of ammonium sulfate can be calculated using the ideal gas law equation:

PV = nRT

Where: P = pressure (atm) V = volume (L) n = moles R = ideal gas constant (0.0821 L·atm/(mol·K)) T = temperature (K)

Given that the total volume of gas produced is 13.44 L at standard temperature and pressure (STP), we can calculate the moles of ammonium sulfate formed.

Using the ideal gas law equation, we can rearrange it to solve for moles:

n = PV / RT

At STP, the pressure is 1 atm and the temperature is 273 K. Substituting these values into the equation, we get:

n = (1 atm) * (13.44 L) / (0.0821 L·atm/(mol·K) * 273 K) = 0.638 mol

Since 2 moles of ammonium sulfate are formed for every 0.638 moles, the moles of ammonium sulfate in the solution is:

0.638 mol * (2 mol/(0.638 mol)) = 2 mol

To calculate the mass fraction of ammonium sulfate, we need to know the total mass of the solution. Unfortunately, the mass of the solution is not provided in the question. Therefore, without this information, we cannot determine the mass fraction of ammonium sulfate in the solution.

Why the Mass of the Evolved Gas is Not Considered in the Solution

You mentioned that the mass of the evolved gas is not considered in the solution provided by an expert. It is important to note that the mass of the evolved gas is not relevant to determining the mass fraction of ammonium sulfate in the solution. The mass fraction is calculated based on the amount of ammonium sulfate present in the solution, not the gas produced during the reaction.

The mass of the solution does not change during the reaction because the reactants and products are all in the liquid phase. The gas produced during the reaction is released into the surroundings and does not contribute to the mass of the solution. Therefore, the mass of the solution remains the same before and after the reaction.

In summary, the mass of the evolved gas is not considered in the calculation of the mass fraction of ammonium sulfate because it does not affect the mass of the solution. The mass fraction is determined solely based on the amount of ammonium sulfate present in the solution.