Chemistry, 21.06.2021 18:40 VamPL

Calculate the molality of each of the following solutions: (a) 14.3 g of sucrose (C12H22O11) in 685 g of water,
(b) 7.15 moles of ethylene glycol (C2H6O2) in 3505 g of water.

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Answer from: beserkerbradley5863

(a) The molality of this solution is 0.0613 $\frac{moles}{kg}$

(b)The molality of this solution is 2.04 $\frac{moles}{kg}$

Explanation:

The molality (m) of a solution is defined as the number of moles of solute present per kg of solvent.

The Molality of a solution is determined by the expression:

$Molality=\frac{number of moles of solute}{kilograms of solvent}$

Molality is expressed in units $\frac{moles}{kg}$

(a) You have 14.3 g of sucrose (C₁₂H₂₂O₁₁), the solute. With the molar mass of sucrose being 342 $\frac{g}{mole}$ , then 14.3 grams of the compound represents the following number of moles:

$14.3 grams*\frac{1 mole}{342 grams} =$ 0.042 moles

Having 685 g= 0.685 kg (being 1000 g= 1 kg) of water, the solvent, molality can be calculated as:

$molality=\frac{0.042 moles}{0.685 kg}$

Solving:

molality= 0.0613 $\frac{moles}{kg}$

The molality of this solution is 0.0613 $\frac{moles}{kg}$

(b) In this case you have 7.15 moles of ethylene glycol (C₂H₆O₂), the solute, in 3505 g (equal to 3.505 kg) of water, the solvent, molality can be calculated as:

$molality=\frac{7.15 moles}{3.505 kg}$

Solving:

molality= 2.04 $\frac{moles}{kg}$

The molality of this solution is 2.04 $\frac{moles}{kg}$

Answer from: Quest

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence, the electronegativity (or the ability to attract electrons) is lessened."

Answer from: Quest

hydrocarbons are organic compounds that contain only hydrogens and carbons. they can be saturated (those which contain only carbon-carbon single bonds) or unsaturated (those which contain carbon-carbon double or triple bonds) in nature. hydrocarbons can undergo several reactions like substitution, elimination etc.

on substituting one or more hydrogen atoms in hydrocarbon it results in the formation of haloalkane. as the halogen atoms are large compared to the carbon and hydrogen atoms, due to which the molecular weight increases and the bond become polar because of presence electronegative halogen atom and results in the increase in boiling point of the haloalkane.

thus, the correct option is (b) that is the boiling point of the new compound increases on substituting a hydrogen atom with a halogen in a hydrocarbon.