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dusya [7]
3 years ago
7

The molar mass is determined by measuring the freezing point depression of an aqueous solution. A freezing point of -5.20°C is r

ecorded for a solution made by dissolving 10.56 g of the compound in 25.0 g water. Determine the empirical formula, molar mass, and molecular formula of the compound.
Chemistry
1 answer:
Dima020 [189]3 years ago
6 0

Answer:

The empirical formula is C2H4O3

The molecular formula is C4H8O6

The molar mass is 152 g/mol

Explanation:

The complete question is: An unknown compound contains only carbon, hydrogen, and oxygen. Combustion analysis of the compound gives mass percents of 31.57% C and 5.30% H. The molar mass is determined by measuring the freezing-point depression of an aqueous solution. A freezing point of -5.20°C is recorded for a solution made by dissolving 10.56 g of the compound in 25.0 g water. Determine the empirical formula, molar mass, and molecular formula of the compound. Assume that the compound is a nonelectrolyte.

Step 1: Data given

Mass % of Carbon = 31.57 %

Mass % of H = 5.30 %

Freezing point = -5.20 °C

10.56 grams of the compound dissolved in 25.0 grams of water

Kf water = 1.86 °C kg/mol

Step 2: Calculate moles of Carbon

Suppose 31.57% = 31.57 grams

moles C = mass C / Molar mass C

moles C = 31.57 grams / 12.0 g/mol = 2.63 moles

Step 3: Calculate moles of Hydrogen:

Moles H = 5.30 grams / 1.01 g/mol

moles H = 5.25 moles

Step 4: Calculate moles of Oxygen

Moles O = ( 100 - 31.57 - 5.30) / 16 g/mol

Moles O = 3.95 moles

Step 5: We divide by the smallest number of moles

C: 2.63 / 2.63 = 1 → 2

H: 5.25/2.63 = 2 → 4

O: 3.95/ 2.63 = 1.5 → 3

The empirical formula is C2H4O3

The molar mass of the empirical formula = 76 g/mol

Step 6: Calculate moles solute

Freezing point depression = 5.20 °C = m * 1.86

m = 5.20 / 1.86

m = 2.80 molal = 2.80 moles / kg

2.80 molal * 0.025 kg = 0.07 moles

Step 7: Calculate molar mass

Molar mass = mass / moles

Molar mass = 10.56 grams / 0.07 moles

Molar mass = 151 g/mol

Step 8: Calculate molecular formula

151 / 76 ≈  2

We have to multiply the empirical formula by 2

2*(C2H4O3) = C4H8O6

The molecular formula is C4H8O6

The molar mass is 152 g/mol

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Anarel [89]

The answer is- SF_{6} is octahedral in electronic and molecular geometry with 6 Fluorine atoms bonded to central atom S.

Lewis structures are the diagrams in which the valence electrons of the atoms of a compound are arranged around the atoms showing the bonding between the atom and the lone pair of electrons existing in the molecule.

Determine the molecular geometry of SF_{6}.

  • Valence Shell Electron Pair Repulsion theory is commonly known as VSEPR theory and it helps to predict the geometry of molecules.
  • According to this theory, electrons are arranged around the central atom of the molecule in such a way that there is minimum electrostatic repulsion between these electrons.
  • Now, calculate the total number of valence electrons in SF_{6}.

Valence\ electrons\ in\ SF_{6}= Valence\ electrons\ in\ S +\ 6(Valence\ electrons\ in\ F)

Valence electrons of S = 6

Valence electrons of F = 7

Thus, the valence electrons in SF_{6} are-

Valence\ number\ of\ electrons\ in\ SF_{6} = (6) + 6(7) = 48\ electrons.

  • The Lewis structure of SF_{6} is - (Image attached).
  • In the structure, the number of atoms bonded to central atom (S) = 6.
  • Number of non-bonding electron pairs on the central atom = 0 (as all the valence electrons are bonded to F).
  • Electronic geometry in case of 6 bond pairs is octahedral.
  • Molecular geometry us also octahedral with bond angles 90°.
  • Central atom is sp3d2 hybridised.
  • SF_{6} is a non-polar molecule.

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7 0
11 months ago
How many grams of Ca(NO3)2 are needed to make 25.0 g of a 15.0% Ca(NO3)2(aq)?
yarga [219]

Answer:

3.75 g.

Explanation:

<em>mass percent is the ratio of the mass of the solute to the mass of the solution multiplied by 100.</em>

<em />

<em>mass % = (mass of solute/mass of solution) x 100.</em>

<em></em>

mass of calcium nitrite = ??? g,

mass of the solution = 25.0 g.

∴ mass % = (mass of solute/mass of solution) x 100

<em></em>

<em>∴ mass of solute (calcium nitrite) = (mass %)(mass of solution)/100</em> = (15.0 %)(25.0 g)/100 = <em>3.75 g.</em>

5 0
3 years ago
The student's lab manual says to mix some of his Na2CO3 solution with an aqueous solution of copper(II) sulfate (CuSO4)
lord [1]

Explanation:

When the student mixed the solution sodium carbonate with solution of copper(II) sulfate ; Copper Hydroxocarbonate , sodium sulfate and carbon dioxide gas was obtained as a products.

The balanced chemical reaction

2Na_2CO_3+2CuSO_4\rightarrow Cu_2(OH)_2CO_3+2Na_2SO_4+CO_2

Where:

Cu_2(OH)_2CO_3 = Copper(II) Hydroxocarbonate

Na_2CO_3 = Sodium carbonate

CuSO_4 = Copper(II) sulfate

Na_2SO_4 = Sodium sulfate

CO_2 = Carbon-dioxide

3 0
3 years ago
Why does the amount of water that flows in a river change during the year?
Ilya [14]
It might change because of the amout of rain that fell in the year and the melting of ice which allows the water amount to increase
7 0
3 years ago
What is the molar mass of 56.75 g of gas exerting a pressure of 2.87 atm on the walls of a 5.29 l container at 230 k?
laiz [17]
We first need to find the number of moles of gas in the container 
PV = nRT
where;
P - pressure - 2.87 atm x 101 325 Pa/atm = 290 802.75 Pa
V - volume - 5.29 x 10⁻³ m³
n - number of moles
R - universal gas constant - 8.314 Jmol⁻¹K⁻¹
T - temperature - 230 K
substituting these values in the equation 
290 802.75 Pa x  5.29 x 10⁻³ m³ = n x 8.314 Jmol⁻¹K⁻¹ x 230 K
n = 0.804 mol
the molar mass = mass present / number of moles
molar mass of gas = 56.75 g / 0.804 mol 
therefore molar mass is 70.6 g/mol 
8 0
3 years ago
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