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Nuetrik [128]
3 years ago
14

The freezing point of 42.19 g of a pure solvent is measured to be 43.17 ºC. When 2.03 g of an unknown solute (assume the van 't

Hoff factor = 1.0000) is added to the solvent the freezing point is measured to be 40.32 ºC. Answer the following questions ( the freezing point depression constant of the pure solvent is 7.67 ºC·kg solvent/mol solute).What is the molality of the solution? m
How many moles of solute are present? mol
What is the molecular weight of the solute? g/molIf the freezing point depression constant of the pure solvent is 7.66 ºC·kg solvent/mol solute calculate the molar mass of the solute. g/mol
Chemistry
1 answer:
vovikov84 [41]3 years ago
4 0

Answer:

The molality of the solution is 0.3716 mol/kg

The number of moles of solute is 0.0157 mol

The molecular weight of the solute is 129.30 g/mol

The molar mass of the solute is 129.32 g/mol

Explanation:

m (molality of the solution) = ∆T/Kf = (43.17 - 40.32)/7.67 = 0.3716 mol/kg

Number of moles of solute = molality × mass of solvent in kilogram = 0.3716 × 0.04219 = 0.0157 mol

Molecular weight of solute = mass/number of moles = 2.03/0.0157 = 129.3 g/mol

When Kf = 7.66 °C.kg/mol

Molar mass = 2.03 ÷ (2.85/7.66 × 0.04219) = 129.32 g/mol

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the spectral lines observed for hydrogen arise from transitions from excited states back to the n=2 principle quantum level. Cal
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where, R_{H} = Rydberg  constant = 1.0973731568508 \times 10^{7} per metre

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Now, for n_{1}= 2 and n_{2}= 6

\frac{1}{\lambda} = 1.0973731568508 \times 10^{7} \times (\frac{1}{2^{2}}-\frac{1}{6^{2}} )

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= 1.0973731568508 \times 10^{7} \times (0.25-0.0278 )

= 1.0973731568508 \times 10^{7} \times 0.23

= 0.2523958\times 10^{7}

\lambda = \frac{1}{0.2523958\times 10^{7}}

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Now, for n_{1}= 2 and n_{2}= 5

\frac{1}{\lambda} = 1.0973731568508 \times  10^{7} \times (\frac{1}{2^{2}}-\frac{1}{5^{2}} )

= 1.0973731568508 \times 10^{7} \times (0.25-0.04 )

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\lambda= \frac{1}{0.230 \times 10^{7}}

= 4.3478 \times 10^{-7} m

= 434.78\times 10^{-9} m

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Now, for n_{1}= 2 and n_{2}= 4

\frac{1}{\lambda} = 1.0973731568508 \times  10^{7} \times (\frac{1}{2^{2}}-\frac{1}{4^{2}} )

=  1.0973731568508 \times 10^{7} \times (0.25-0.0625 )

= 1.0973731568508 \times 10^{7} \times (0.1875 )

= 0.20575 \times 10^{7}

\lambda= \frac{1}{0.20575 \times 10^{7}}

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\frac{1}{\lambda} = 1.0973731568508 \times 10^{7} \times (\frac{1}{2^{2}}-\frac{1}{3^{2}} )

=  1.0973731568508 \times 10^{7} \times (0.25-0.12 )

=  1.0973731568508 \times 10^{7} \times (0.13 )

= 0.1426585\times 10^{7}

\lambda= \frac{1}{0.1426585\times 10^{7}}

= 7.0097 \times 10^{-7} m

= 700.97 \times 10^{-9} m

= 700.97 nm



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