Question

Помогите с химией и поподробнее, пожалуйста При сжигании 4,3 г. органического вещества получили 6,72 л. углекислого газа и 6,3 г. воды. Относительная плотность вещества по водороду равна 43. Какова молекулярная формула этого вещества?

Answer 1

Ответ:

дано

m(в-ва) = 4.3 g

V(CO2) = 6.72 L

m(H2O) - 6.3  g

D(H2) = 43

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Формулу(в-ва) - ?

1) определяем количества  углерода

n(C) = n(CO2) = V(CO2)  / Vm  = 6.72 / 22.4 = 0.3 mol

2)определяем массу  углерода

M(C) = 12 g/mol

m(C) = n(C) * M(C)  = 0.3 * 12 = 3.6 g

3) определяем количества  водорода

n(H) = 2n(H2O) = 2*m(H2O) / M(H2O)  ,  M(H2O) = 18 g/mol

n(H) = 2n(H2O) = 2*m(H2O) / M(H2O) = 2 * 6.3 / 18 = 0.7 mol

4) определяем массу  водорода

M(H)  =1 g/mol

m(H) = n(H) * M(H) = 1 * 0.7  = 0.7 g

5) Зная массу вещества , зная массу углерода и водорода , определяем наличие массы кислорода

m(O) = m(в-ва) - ( m(C) + m(H)) = 4.3 - ( 3.6 + 0.7) = 0 g

6) В этом соединении атом кислорода отсутствует , след - но молекула состоит из углерода и водорода.

7) Определяем молярная массу вещества

M(CxHy) = D(H2) * 2 = 43 * 2 = 86 g/mol

8) n(C) : n(H)  = 0.3 : 0.7 = 3 : 7

CxHy = 3 : 7 ==> C3H7

M(C3H7) = 12*3 + 1*7 = 43 g/mol

9) определяем во сколько молекулярная масса данного вещества , больше молекулярной массы , которой получилось

M(CxHy) / M(CxHy) = 86 / 43 = 2 раза

10) Нужно получившую молекулярную массу  умножить на 2 и получим нужную молекулярную массу исходного вещества

M(C3H7) * 2 = M(C6H14)  -  ГЕКСАН

ответ C6H14

Объяснение:

Answer 2

Molecular Formula of the Organic Substance

To determine the molecular formula of the organic substance, we need to analyze the given information about the products of its combustion.

According to the information provided, when 4.3 g of the organic substance is burned, 6.72 L of carbon dioxide (CO2) and 6.3 g of water (H2O) are produced.

To find the molecular formula, we need to calculate the number of moles of carbon dioxide and water produced.

1. Calculate the number of moles of carbon dioxide (CO2): - The molar mass of carbon dioxide (CO2) is 44.01 g/mol (12.01 g/mol for carbon + 2 * 16.00 g/mol for oxygen). - The number of moles of carbon dioxide can be calculated using the formula: moles = mass / molar mass. - Substituting the values, we get: moles of CO2 = 6.72 L * (1 mol/22.4 L) * (44.01 g/mol) = 13.44 g / 44.01 g/mol = 0.305 mol.

2. Calculate the number of moles of water (H2O): - The molar mass of water (H2O) is 18.02 g/mol (2 * 1.01 g/mol for hydrogen + 16.00 g/mol for oxygen). - The number of moles of water can be calculated using the formula: moles = mass / molar mass. - Substituting the values, we get: moles of H2O = 6.3 g / 18.02 g/mol = 0.349 mol.

Now, let's calculate the empirical formula of the organic substance using the moles of carbon dioxide and water produced.

3. Determine the empirical formula: - The empirical formula represents the simplest whole-number ratio of atoms in a compound. - To find the empirical formula, we need to divide the number of moles of each element by the smallest number of moles. - From the calculations above, we have 0.305 mol of carbon and 0.349 mol of hydrogen. - Dividing both values by 0.305 (the smallest number of moles), we get approximately 1 mol of carbon and 1.14 mol of hydrogen. - To simplify the ratio, we can multiply both values by 7 to get 7 moles of carbon and 8 moles of hydrogen. - Therefore, the empirical formula of the organic substance is C7H8.

However, we still need to determine the molecular formula of the organic substance. To do this, we need additional information.

The given relative density of the substance with respect to hydrogen is 43. Relative density is defined as the ratio of the density of a substance to the density of a reference substance (in this case, hydrogen).

4. Determine the molar mass and molecular formula: - The relative density is related to the molar mass of a substance. - The molar mass of hydrogen (H2) is approximately 2.02 g/mol. - The molar mass of the organic substance can be calculated using the formula: molar mass = relative density * molar mass of hydrogen. - Substituting the values, we get: molar mass = 43 * 2.02 g/mol = 87.26 g/mol.

To find the molecular formula, we need to determine the ratio between the empirical formula mass and the molar mass.

5. Calculate the molecular formula: - The empirical formula mass of C7H8 can be calculated by summing the atomic masses of carbon and hydrogen: (7 * 12.01 g/mol) + (8 * 1.01 g/mol) = 92.15 g/mol. - The ratio between the empirical formula mass and the molar mass is: 87.26 g/mol / 92.15 g/mol = 0.947. - Since the ratio is close to 1, the molecular formula is likely the same as the empirical formula. - Therefore, the molecular formula of the organic substance is also C7H8.

In conclusion, the molecular formula of the organic substance is C7H8.