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jenniferalvarez360
28.06.2020 •
Chemistry
Suppose that you add 27.6 g of an unknown molecular compound to 0.250 kg of benzene, which has a K f of 5.12 oC/m. With the added solute, you find that there is a freezing point depression of 3.69 oC compared to pure benzene. What is the molar mass of the unknown compound
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Ответ:
Molar mass is the mass of the one mole of substance. The molar mass of the given unknown compound is 153.3 g/mol.
Molality of the compound can be calculated using
ΔT = i Kf m
Where,
ΔT = freezing point depression = 3.69 °C
i = Van't Hoff factor of Benzene = 1
Kf = constant of freezing = 5.12 °C/m
m = molality = ?
Put the values in the equation,
3.69 = 1 x 5.12 x m
m = 0.72 molal
Number of moles of the compound,
So, molar mass of the unknown compound,
The molar mass of the given unknown compound is 153.3 g/mol.
To know more about molar mass,
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Ответ:
The molar mass of the unknown compound is 153.3 g/mol
Explanation:
Step 1: Data given
Mass of an unknown molecular compound = 27.6 grams
Mass of benzene = 0.250 kg
Kf of benzene = 5.12 °C/m
freezing point depression of 3.69 °C
Step 2: Calculate molality
ΔT = i*Kf*m
⇒with ΔT = reezing point depression of 3.69 °C
⇒with i = the van't Hoff factor of Benzene = 1
⇒with Kf = 5.12 °C/m
⇒ with m = molality = moles unknown compound / mass of benzene
3.69 = 1 * 5.12 * m
m = 0.72 molal
Step 3: Calculate moles of the unknown compound
molality = moles / mass benzene
0.72 molal = moles / 0.250 kg
Moles = 0.72 m * 0.250 kg
Moles = 0.18 moles
Step 4: Calculate molar mass of the unknown compound
molar mass = mass / moles
Molar mass = 27.6 grams / 0.18 moles
Molar mass = 153.3 g/mol
The molar mass of the unknown compound is 153.3 g/mol
Ответ:
I will start with K2Cr2O7 because I believe that Cr is the best candidate to reduce its oxidation number in 3 units.
In K2Cr2O7:
- K has oxidation state of 1+, then K2 has a charge of 2* (1+) = 2+.
- O has oxidation state of 2*, then O7 has a charge of 7* (2-) = 14-.
That makes that Cr2 has charge of 14 - 2 = +12, so each Cr has +12/2 = +6 oxidation state.
In Cr2O3:
- O has oxidation state of 2-, then O3 has charge 3 * (2-) = - 6
- Then, Cr2 has charge 6+, and each Cr has charge 6+ / 2 = 3+.
So, we have seen that Cr reduced its oxidation state in 3 units, from 6+ to 3+.
Cr has a change in oxidation number of - 3.