Question

Навеску гидрокарбоната натрия массой 42г нагревали в течение некоторого времени. При растворении полученного твёрдого остатка в избытке соляной кислоте выделилось 6.72 л(н.у.) газа. Определите сколько процентов гидрокабоната разложилось.

Answer 1

Дано:m(NaHCO3)=42 rV(CO2)=6,72 лНайти:w(NaHCO3)-?
Решение.2NaHCO3 =t= Na2CO3 + H2O + CO2  (1)Na2CO3 + 2HCl = 2NaCl + CO2 + H2O  (2)n(CO2)=V(CO2)/Vm = 6,72 л/22,4 л/моль = 0,3 мольИз УХР2 видно, что n(Na2CO3)=n(CO2)=0.3 мольИз УХР1 видно, что n(NaHCO3)=0,5n(Na2CO3)n(NaHCO3) = 0,5*0,3 моль = 0,15 мольM(NaHCO3) = 84 г/мольm'(NaHCO3) = n*M = 0,15 моль*84 г/моль = 12,6 гw(NaHCO3) = m'(NaHCO3)/m(NaHCO3) = 0.3 или 30%Ответ: 30%

Answer 2

Problem Analysis

We are given that 42 grams of sodium bicarbonate (NaHCO3) were heated for some time. The resulting solid residue was dissolved in an excess of hydrochloric acid (HCl), and 6.72 liters of gas were evolved. We need to determine the percentage of sodium bicarbonate that decomposed during this process.

Solution

To solve this problem, we need to calculate the amount of sodium bicarbonate that decomposed and then find the percentage of decomposition.

1. Calculate the molar mass of sodium bicarbonate (NaHCO3): - The molar mass of Na is 22.99 g/mol. - The molar mass of H is 1.01 g/mol. - The molar mass of C is 12.01 g/mol. - The molar mass of O is 16.00 g/mol. - Adding these values together, we get: Molar mass of NaHCO3 = (22.99 g/mol) + (1.01 g/mol) + (12.01 g/mol) + (3 * 16.00 g/mol) = 84.01 g/mol.

2. Calculate the number of moles of sodium bicarbonate used: - We can use the formula: moles = mass / molar mass. - Substituting the given values, we get: Moles of NaHCO3 = 42 g / 84.01 g/mol = 0.499 moles.

3. Calculate the volume of carbon dioxide gas evolved: - According to the ideal gas law, the volume of a gas is directly proportional to the number of moles of the gas. - Since the volume of gas evolved is given as 6.72 liters, we can say: Moles of CO2 = 0.499 moles.

4. Calculate the percentage of sodium bicarbonate that decomposed: - The balanced chemical equation for the decomposition of sodium bicarbonate is: 2 NaHCO3(s) -> Na2CO3(s) + H2O(g) + CO2(g). - From the equation, we can see that 2 moles of sodium bicarbonate produce 1 mole of carbon dioxide gas. - Therefore, the moles of sodium bicarbonate that decomposed can be calculated as: Moles of decomposed NaHCO3 = (0.499 moles of CO2) * (2 moles of NaHCO3 / 1 mole of CO2) = 0.998 moles. - Finally, the percentage of sodium bicarbonate that decomposed can be calculated as: Percentage of decomposition = (moles of decomposed NaHCO3 / moles of NaHCO3 used) * 100% = (0.998 moles / 0.499 moles) * 100% = 200%.

Answer

The percentage of sodium bicarbonate that decomposed during the process is 200%.

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