Question

При сжигании 4,6 г вещества образуется 8,8 г CO₂ и 5,4 г H₂O. Плотность паров этого вещества по воздуху равна 1,59. Определить молекулярную формулу этого вещества.

Answer 1

Дано:

m (в-ва) = 4,6 г

m (CO2) = 8,8 г

m (Н2О) = 5,4 г

D(возд) = 1,59

Решение:

M(в-ва) = D(возд) ∙ M(возд) = 1,59 ∙ 29 = 46,11 г\моль

4,6  г                  8,8 г            5,4 г

CxHy + O2 = x CO2    +    y/2H2O 

46,11 г            х∙44 г             9 ∙ у г       

4,6 г -----   8,8 г       

46,11 г ------ х∙44 г          

х = 46,11 г ∙ 8,8 г \ 4,6 г ∙ 44 г = 2

4,6 г   -----   5,4 г

46,11 г ------ 9 ∙ у г       

у  = 46,11 г ∙ 5,4 г \ 4,6 г ∙ 9 г = 6

х: y = 2:6 =  CxHy  = C2H6

Ответ: С2Н6 - этан

получается так, но возможно в задаче ошибка

 

 

Answer 2

Calculation of the Molar Mass

To determine the molecular formula of the substance, we need to calculate its molar mass. We are given the mass of carbon dioxide (CO₂) and water (H₂O) produced when 4.6 g of the substance is burned.

The molar mass of CO₂ is 44 g/mol, and the molar mass of H₂O is 18 g/mol.

Let's calculate the number of moles of CO₂ and H₂O produced:

- Moles of CO₂ = Mass of CO₂ / Molar mass of CO₂ = 8.8 g / 44 g/mol = 0.2 mol - Moles of H₂O = Mass of H₂O / Molar mass of H₂O = 5.4 g / 18 g/mol = 0.3 mol

Now, let's calculate the number of moles of the substance:

- Moles of the substance = Moles of CO₂ or H₂O (since they have a 1:1 ratio) = 0.2 mol

The molar mass of the substance can be calculated using the formula:

Molar mass = Mass of the substance / Moles of the substance

- Molar mass = 4.6 g / 0.2 mol = 23 g/mol

Determining the Empirical Formula

To determine the empirical formula, we need to find the ratio of the elements present in the substance. From the balanced chemical equation for the combustion reaction, we know that 1 mole of the substance produces 1 mole of CO₂ and 1 mole of H₂O.

Therefore, the empirical formula of the substance is CH₂O.

Determining the Molecular Formula

To determine the molecular formula, we need to know the molar mass of the empirical formula. The molar mass of CH₂O can be calculated as follows:

- Molar mass of CH₂O = (Molar mass of C) + 2 * (Molar mass of H) + (Molar mass of O) - Molar mass of CH₂O = (12 g/mol) + 2 * (1 g/mol) + (16 g/mol) = 30 g/mol

The molecular formula can be determined by dividing the molar mass of the substance by the molar mass of the empirical formula:

- Molecular formula = Molar mass of the substance / Molar mass of the empirical formula - Molecular formula = 23 g/mol / 30 g/mol = 0.77

Since the result is less than 1, it means that the empirical formula (CH₂O) is also the molecular formula of the substance.

Therefore, the molecular formula of the substance is CH₂O.