Respuesta :
Answer: The molecular formula of the compound is [tex]C_4H_{10}O_4[/tex]
Explanation:
To calculate the concentration of solute, we use the equation for osmotic pressure, which is:
[tex]\pi=iMRT[/tex]
Or,
[tex]\pi=i\times \frac{\text{Mass of solute}\times 1000}{\text{Molar mass of solute}\times \text{Volume of solution (in mL)}}\times RT[/tex]
where,
[tex]\pi[/tex] = osmotic pressure of the solution = 2.13 atm
i = Van't hoff factor = 1 (for non-electrolytes)
Given mass of compound = 2.04 g
Volume of solution = 175.0 mL
R = Gas constant = [tex]0.0821\text{ L atm }mol^{-1}K^{-1}[/tex]
T = temperature of the solution = [tex]25^oC=[273+25]=298K[/tex]
Putting values in above equation, we get:
[tex]2.13atm=1\times \frac{2.04\times 1000}{\text{Molar mass of compound}\times 175.0}\times 0.0821\text{ L.atm }mol^{-1}K^{-1}\times 298K\\\\\text{Molar mass of compound}=\frac{1\times 2.04\times 1000\times 0.0821\times 298}{2.13\times 175.0}=133.9g/mol[/tex]
- Calculating the molecular formula:
The chemical equation for the combustion of compound having carbon, hydrogen and oxygen follows:
[tex]C_xH_yO_z+O_2\rightarrow CO_2+H_2O[/tex]
where, 'x', 'y' and 'z' are the subscripts of carbon, hydrogen and oxygen respectively.
We are given:
Mass of [tex]CO_2=36.26g[/tex]
Mass of [tex]H_2O=14.85g[/tex]
We know that:
Molar mass of carbon dioxide = 44 g/mol
Molar mass of water = 18 g/mol
For calculating the mass of carbon:
In 44 g of carbon dioxide, 12 g of carbon is contained.
So, in 36.26 g of carbon dioxide, [tex]\frac{12}{44}\times 36.26=9.89g[/tex] of carbon will be contained.
For calculating the mass of hydrogen:
In 18 g of water, 2 g of hydrogen is contained.
So, in 14.85 g of water, [tex]\frac{2}{18}\times 14.85=1.65g[/tex] of hydrogen will be contained.
Mass of oxygen in the compound = (22.08) - (9.89 + 1.65) = 10.54 g
To formulate the empirical formula, we need to follow some steps:
- Step 1: Converting the given masses into moles.
Moles of Carbon = [tex]\frac{\text{Given mass of Carbon}}{\text{Molar mass of Carbon}}=\frac{9.89g}{12g/mole}=0.824moles[/tex]
Moles of Hydrogen = [tex]\frac{\text{Given mass of Hydrogen}}{\text{Molar mass of Hydrogen}}=\frac{1.65g}{1g/mole}=1.65moles[/tex]
Moles of Oxygen = [tex]\frac{\text{Given mass of oxygen}}{\text{Molar mass of oxygen}}=\frac{10.54g}{16g/mole}=0.659moles[/tex]
- Step 2: Calculating the mole ratio of the given elements.
For the mole ratio, we divide each value of the moles by the smallest number of moles calculated which is 0.659 moles.
For Carbon = [tex]\frac{0.824}{0.659}=1.25\approx 1[/tex]
For Hydrogen = [tex]\frac{1.65}{0.659}=2.5[/tex]
For Oxygen = [tex]\frac{0.659}{0.659}=1[/tex]
Converting the mole fraction into whole number by multiplying the mole fraction by '2'
Mole fraction of carbon = (1 × 2) = 2
Mole fraction of oxygen = (2.5 × 2) = 5
Mole fraction of hydrogen = (1 × 2) = 2
- Step 3: Taking the mole ratio as their subscripts.
The ratio of C : H : O = 2 : 5 : 2
The empirical formula for the given compound is [tex]C_2H_5O_2[/tex]
For determining the molecular formula, we need to determine the valency which is multiplied by each element to get the molecular formula.
The equation used to calculate the valency is:
[tex]n=\frac{\text{Molecular mass}}{\text{Empirical mass}}[/tex]
We are given:
Mass of molecular formula = 133.9 g/mol
Mass of empirical formula = 61 g/mol
Putting values in above equation, we get:
[tex]n=\frac{133.9g/mol}{61g/mol}=2[/tex]
Multiplying this valency by the subscript of every element of empirical formula, we get:
[tex]C_{(2\times 2)}H_{(5\times 2)}O_{(2\times 2)}=C_4H_{10}O_4[/tex]
Hence, the molecular formula of the compound is [tex]C_4H_{10}O_4[/tex]
The molecular formula of the compound is C4H12O4.
π = icRT
π = osmotic pressure
c = concentration
R = molar constant
T = temperature
Now we know that; c = n/V
n = number of moles
V = volume
π = i(n/V)RT
π =inRT/V
n = πV/iRT
n = 2.13 atm × 0.175 L/1 × 0.082 atmLK-1mol-1 × 298 K
n = 0.3675/24.436
n = 0.015 moles
number of moles = mass/molar mass
Molar mass = mass/ number of moles = 2.04 g /0.015 moles = 136 g/mol
From the combustion information;
mass of C = 36.26 g/44 × 12 = 9.9 g
Number of moles of C = 9.9 g/12 g/mol = 0.825 moles
Mass of H = 14.85 g/18 × 2 = 1.65 g
Number of moles of H = 1.65 g/ 1 g/mol = 1.65 moles
Mass of O = 22.08 g - (9.9 g + 1.65 g) = 10.53 g
Number of moles of oxygen = 10.53 g/16 g/mol = 0.658 moles
To obtain the empirical formula, we divide through by the least number of moles;
C - 0.825 moles/0.658 moles, H - 1.65 moles/0.658 moles, O - 0.658 moles/0.658 moles
C - 1, H - 3, O - 1
The empirical formula of the compound is CH3O
The molecular formula of the compound is obtained thus;
[12 + 3 + 16]n = 136
n = 136/31
n = 4
The molecular formula is C4H12O4.
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