Chemistry, 29.08.2019 09:50 kuadirkennedy

Which substance has the lowest vapor pressure at 75°c?
(1) water (3) propanone
(2) ethanoic acid (4) ethanol

Answers: 2

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Vapor pressure is a colligative property. This means that intermolecular forces play a large role in how volatile a substance is. We can thus assume that the substance and or liquid in this case with the strongest intermolecular forces will have the lowest vapor pressure, as intermolecular attraction will oppose the vaporizing forces created by temperature and or kinetic energy. The strongest of such intermolecular forces is hydrogen bonding, and given some knowledge of boiling point we can find the answer. In this case:
water: has hydrogen bonding, dispersion, and dipole forces for intermolecular attraction
ethanoic acid: a carboxylic acid has one polar end with a negative charge as CH3COOH turns to CH3COO-. Hydrogen bonding is also present in pure solutions.
Propanone: is a ketone and has an electronegative oxygen attached to a carbon, but does not exhibit hydrogen bonding since the O is not attached to a hydrogen.
Ethanol: Like water exhibits hydrogen bonding, not as strong but more dispersion forces.

Next we must understand boiling points
Water: 100˚C
Ethanoic Acid: 118˚C
Propanone: 56˚C
Ethanol: 78˚C
Given this knowledge we can order the liquids in terms of decreasing volatility or decreasing vapor pressure. We now notice that Ethanoic acid, or acetic acid will have the lowest vapor pressure at 75˚C
Which substance has the lowest vapor pressure at 75°c? (1) water (3) propanone (2) ethanoic acid (4

Which substance has the lowest vapor pressure at 75°c? (1) water (3) propanone (2) ethanoic acid (4

Answer from: Quest

- calcium has greater affinity to bond with electron receptors than hydrogen does and hence, it has the ability to replace hydrogen in most of its compounds.

- lithium has 2 valence electrons in the product because it can make only 1 bond with hydrogen. beryllium has 4 valence electrons in the product because it can only make 2 bonds. it has fewer electrons than neon and can react with electron donors. each hydrogen has 2 valence electrons, the same as helium.

- the covalent bond formed between carbon and hydrogen is polar because carbon is more electronegative than hydrogen and it attracts the bonded electron pair closer to itself, thus giving hydrogen a partial positive charge.

- a hydrogen bond is a relatively weak bond that hydrogen atoms make with the electronegative atoms nitrogen, oxygen or fluorine.

so the best choice is a.) 2 calcium (ca) atoms

Answer from: Quest

fe 55.85 g/mol and h2o 18.02 g/mol.

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Which substance has the lowest vapor pressure at 75°c?
(1) water (3) propanone
(2) etha...

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