Tag Archives: molar mass

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Paul asks…

Can anyone help me solve this molality problem?

A 2.42 m solution of the solute diethyl ether dissolved in the solvent C4H8O is available. Calculate the mass (g) of the solution that must be taken to obtain 1470 g of (C2H5)2O.

weight loss cardiff answers:

Moles (C2H5)2O = 1470 g/74.123 g/mol=19.8

m = moles solute / Kg solvent

2.42 = 19.8 / Kg solvent

Mass solvent = 8.18 Kg

mass solution = mass solute + mass solvent = 8.18 +1.47 Kg=9.65 Kg

Maria asks…

How to determine lowest melting point?

So I have an exam coming up and I’d like to get some tips on how I can determine the lowest melting point. One of the questions I had on an exam before was:

Which if these should have the lowest mp temperature?
A) Diethyl ether
B) 2-methyl butane
C) N,N, Dimethyl ethylamine
D) Butyl amine

I know the answer is B, but how do we know that? Thanks in advanced =)
Awesome Aj! Thanks for your help =)

weight loss cardiff answers:

All of these compounds have London dispersion forces. LDF strength is respective to molar mass so the lower the molar mass, the lower the strength of the LDF and consequently the less energy is required to break the IMF and melt.

Steven asks…

How do you find a value for Kp?

You have 50mg of benzoic acid dissolved in 3mL of diethyl ether.This is extracted with 3mL of H2O.The ether layer is removed and dried yeilding 45mg of benzoic acid. What is the Kp value for the ether/water solution

weight loss cardiff answers:

Kp is partitioning coefficient: it is ratio of concentration in organic phase versus concentration in water phase. Since the volumes are the same in this experiment, we can take the ratio of masses: so Kp=45/5 = 9.

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Mark asks…

Chlorocyclohexane + Mg in diethyl ether can be what kind of reaction?

We’ve been studying alkanes alkenes and alkynes but so far I haven’t seen a reaction with Mg and diethyl ether. What kind of alkane reaction can that be?

weight loss cardiff answers:

This is a Grignard reaction to form the Grignard reagent cyclohexylmagnesium chloride. Grignard reactions are reactions between halogenoalkanes/arenes and magnesium to form Grignard reagents which are nucleophiles and are used in synthesis to add alkyl/aryl groups to a compound.

Ruth asks…

What is the heat required to vaporize 80.0 g of liquid diethyl ether, (C2H5)2O, at its boiling point?

The ΔH° of vaporization of diethyl ether is 26.0 kJ/mol. Use a molar mass with at least as many significant figures as the data given.

weight loss cardiff answers:

Know: MM=74.12 g/mol (C2H5)O2
want: x kJ

step 1: start with g, go to mol, go to kJ
step 2: check ans

80 g x(mol/74.12 g) x(26 kJ/mol)=28.1 kJ

Nancy asks…

What is the density of Diethyl Ether?

Diethyl ether, (C2H5)2O, vaporizes easily at room temperature. If the vapor exerts a pressure of 233mm Hg in a flask at 25’C, what is the density of the vapor?

weight loss cardiff answers:

Density = mass/volume

Since mass is the number of moles (n) * molar mass (M), density = nM/V

According to the ideal gas law, PV = nRT. Therefore, n = PV/RT

Plug that in for n in the density equation to get

density = PVM/(RTV)

The V’s cancel, so the final equation for density is

density = PM/RT

Convert the vapor pressure of 233 mmHg to 1 atm (1 atm = 760 mmHg), convert the temperature from Celsius to Kelvin (Celcius + 273 = Kelvin), and use R = 0.0821 L*atm / (mol*K). Find molar mass of diethyl ether

C = 12.01 x 4 = 48.04g
H = 1.01 x 10 = 10.10g
O = 16.00 x 1 = 16.00g

molar mass M = 74.14g/mol

density = (233 mmHg * 1 atm / 760 mmHg) * 74.14g/mol / (298 K * 0.0821) = 0.93 g/L

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