Question

При сжигании органического вещества массой 6 г образовалось 6,72 л углекислого газа (н.у.) и 7,2 г воды. Плотность паров неизвестного вещества по воздуху равна 2,07 . определите молекулярную формулу вещества.

Answer 1

Объяснение:

CxHyOz

n(CO2) = n(C) = V(CO2)/M(CO2) = 6.72/22,4 = 0,3 моль

m(C) = 0.3*12 = 3.6 г

n(H) = 2*n(H2O) = 2*m(H2O)/M(H2O) = 2*7.2/18 = 0.8моль

m(H) = 0.8 г

Mr(в-ва) = Д(возд)*M(возд) = 2.07*29 = 60.03 г/моль

m(в-ва) - m(С) - m(H) = 6-3.6-0.8 = 1.6 г

n(O) = 1.6/16 = 0.1 моль

x : y : z = 0.3 : 0,8 : 0,1 = 3:8:1

С3Н8О

M(С3Н8О) = 12*3+8*1+13 = 60 г/моль

Answer 2

Problem Analysis

We are given the following information: - Mass of organic substance burned: 6 g - Volume of carbon dioxide produced: 6.72 L (at standard temperature and pressure) - Mass of water produced: 7.2 g - Density of the unknown substance's vapor: 2.07 (relative to air)

We need to determine the molecular formula of the unknown substance.

Solution

To solve this problem, we need to calculate the number of moles of carbon dioxide and water produced. Then, we can use the mole ratios to determine the empirical formula of the unknown substance. Finally, we can use the density of the vapor to determine the molar mass and molecular formula of the substance.

Let's start by calculating the number of moles of carbon dioxide and water produced.

1. Calculate the number of moles of carbon dioxide: - The molar volume of a gas at standard temperature and pressure (STP) is 22.4 L/mol. - Given that the volume of carbon dioxide produced is 6.72 L, we can calculate the number of moles using the formula: Moles of carbon dioxide = Volume of carbon dioxide / Molar volume at STP - Substituting the values, we get: Moles of carbon dioxide = 6.72 L / 22.4 L/mol

2. Calculate the number of moles of water: - The molar mass of water (H2O) is 18 g/mol. - Given that the mass of water produced is 7.2 g, we can calculate the number of moles using the formula: Moles of water = Mass of water / Molar mass of water - Substituting the values, we get: Moles of water = 7.2 g / 18 g/mol

Now that we have the number of moles of carbon dioxide and water, we can determine the empirical formula of the unknown substance.

3. Determine the empirical formula: - The empirical formula represents the simplest whole-number ratio of atoms in a compound. - To determine the empirical formula, we need to find the ratio of moles of carbon dioxide to moles of water. - Divide the moles of carbon dioxide and water by their respective smallest values to find the ratio. - The empirical formula will be the whole-number ratio of moles obtained.

Next, we need to determine the molar mass and molecular formula of the unknown substance using the density of its vapor.

4. Calculate the molar mass of the unknown substance: - The molar mass of a substance is the mass of one mole of that substance. - We can calculate the molar mass using the formula: Molar mass = Mass of substance / Moles of substance - Substituting the values, we get: Molar mass = 6 g / Moles of substance

5. Determine the molecular formula: - The molecular formula represents the actual number of atoms of each element in a molecule. - To determine the molecular formula, we need to know the molar mass of the substance and the empirical formula. - Divide the molar mass of the substance by the molar mass of the empirical formula to find the ratio. - The molecular formula will be the whole-number ratio of the empirical formula obtained.

Let's calculate the values step by step.

Calculation

1. Calculate the number of moles of carbon dioxide: - Moles of carbon dioxide = 6.72 L / 22.4 L/mol

2. Calculate the number of moles of water: - Moles of water = 7.2 g / 18 g/mol

3. Determine the empirical formula: - Divide the moles of carbon dioxide and water by their respective smallest values to find the ratio.

4. Calculate the molar mass of the unknown substance: - Molar mass = 6 g / Moles of substance

5. Determine the molecular formula: - Divide the molar mass of the substance by the molar mass of the empirical formula to find the ratio.

Answer

To determine the molecular formula of the unknown substance, we need to calculate the number of moles of carbon dioxide and water produced. Then, we can use the mole ratios to determine the empirical formula of the unknown substance. Finally, we can use the density of the vapor to determine the molar mass and molecular formula of the substance.

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