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Serga [27]
3 years ago
10

in order to find the molar mass of an unknown compound, a research scientist prepared a solution of 0.930 g of an unknown in 125

g of a solvent. The pure solvent had a freezing point of 74.2 degrees celcius, and the solution had a freezing point of 73.4 degrees celcius. Given the solvents freezing point depreesion contant, Kf=5.50 degrees celcius/m, find the molar mass of the unknown
Chemistry
1 answer:
PtichkaEL [24]3 years ago
3 0

Answer:

Molar mass→ 0.930 g / 6.45×10⁻³ mol = 144.15 g/mol

Explanation:

Let's apply the formula for freezing point depression:

ΔT = Kf . m

ΔT = 74.2°C - 73.4°C → 0.8°C

Difference between the freezing T° of pure solvent and freezing T° of solution

Kf = Cryoscopic constant → 5.5°C/m

So, if we replace in the formula

ΔT = Kf . m → ΔT / Kf = m

0.8°C / 5.5 m/°C = m → 0.0516 mol/kg

These are the moles in 1 kg of solvent so let's find out the moles in our mass of solvent which is 0.125 kg

0.0516 mol/kg . 0.125 kg = 6.45×10⁻³ moles. Now we can determine the molar mass:

Molar mass (mol/kg) → 0.930 g / 6.45×10⁻³ mol = 144.15 g/mol

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Volgvan

Explanation:

Atomic number is defined as the number of an element which represents total number of protons.

When an atom is neutral then it means it contains same number of protons and electrons.

On the other hand, atomic mass is defined as the sum of total number of protons and neutrons present in an atom.

Protons of every element remains fixed because it shows the identity of each element but if we change the number of neutrons then also identity of the atom will remain fixed. This is because changing the number of neutrons will not show any change in number of protons.

For example, ^{2}_{1}H and ^{3}_{1}H are isotopes of hydrogen and they have same number of protons but different number of neutrons.

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Answer:

Pentafluorobenzene: 11,92 min

Benzene: 12,14 min

Explanation:

<em>Retention time of pentafluorobenzene is 12,98 min and 13,20 min of benzene.</em>

The adjusted retention time is the time an analyte spends in the column not the stationary phase. As time of unretained solute is 1,06 min the adjusted retention time for an analyte is:

tr' = tr - 1,06min

For pentafluorobenzene:

tr' = 12,98min - 1,06min = <em>11,92 min</em>

For benzene:

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<em></em>

I hope it helps!

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Thus, Q = MCΦ

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Mass of silver = ?

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Φ = 65°C

Then, Q = MCΦ

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