CHEM 205 Lecture Notes - Lecture 5: Covalent Bond, Strong Electrolyte, Sodium Chloride

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20 Feb 2018

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3. 4 aqueous solutions: substances dissolved in water: water is a common solvent, a molecular compound with polar covalent bonds, molecule has slightly positive region & slightly negative region, bent geometry (v-shaped) Many ionic compounds are water soluble (but not all: polar water molecules interact well with ions (=charged species, due to electrostatic attractions between partial & full charges, water (cid:373)ole(cid:272)ules surrou(cid:374)d or (cid:862)h(cid:455)drate(cid:863) the io(cid:374)s. Ionic compounds (salts): bonds between ions break, polyatomic ions remain intact, molecular compounds: Intact molecules disperse: covalent bonds do not break, remember: any solution containing ions has a neutral ratio of charges. If a solution contains ions: current can pass through it: measure electrical conductivity to test for presence of ions (cid:862)ele(cid:272)trol(cid:455)te(cid:863): des(cid:272)ri(cid:271)es a(cid:271)ilit(cid:455) of solutio(cid:374)/su(cid:271)sta(cid:374)(cid:272)e to (cid:272)o(cid:374)du(cid:272)t, solutions: if contain ions, substances: if yield ions when dissolved in water. Non-electrolyte: high concentration of, quantitatively yield ions, conducts current efficiently. Low concentration of ions: conducts current poorly dissociated ions when dissolved, nacl, hno3.

Related Questions

The following table presents the solubilities of several gases in water at 25 °C under a total pressure of gas and water vapor of 1 atm. (a) What volume of CH₄(g) under standard conditions of temperature and pressure is contained in 4.0 L of a saturated solution at 25 °C? (b) Explain the variation in solubility among the hydrocarbons listed (the first three compounds), based on their molecular structures and intermolecular forces. (c) Compare the solubilities of O₂, N₂, and NO, and account for the variations based on molecular structures and intermolecular forces. (d) Account for the much larger values observed for H₂S and SO₂ as compared with the other gases listed. (e) Find several pairs of substances with the same or nearly the same molecular masses (for example, C₂H₄ and N₂), and use intermolecular interactions to explain the differences in their solubilities.

The corresponding volume is

b) All three molecules are nonpolar and form very weak interactions with the water molecules. The solubility of ethane is higher that the solubility of methane as ethane is more massive molecule and forms stronger dispersion forces with the water molecule. Ethene is the most soluble gas as the C atoms in ethene are planar, sp² hybridized, and there are π electrons in the orbitals perpendicular to the carbon atoms. π electrons are less tightly held by the nucleus than σ electrons, allowing the dipole of water molecule to disturb the electron density more easily, leading to stronger dipole-induced dipole interactions.

c) The molecular weight is similar for three gases. O₂ and N₂ are nonpolar gases, but more water molecules surround O₂ as it is larger molecule. The O–O bond (double bond) is longer than N–N bond (triple bond). The water attracts nonpolar gases through the weak dipole-induced dipole interactions. NO is the most soluble gas as it has polar bond and the overall molecule is polar as it is linear structure. Water dissolves it via stronger dipole-dipole interactions.

d) H₂S is capable to form weak hydrogen bonds with the water molecules, and these interactions are much stronger than dipole-dipole and dispersion forces. SO₂ is even more soluble in water as it reacts with the water forming H₂SO₃. The very high values for the solubility of gas are the sign that the gas chemically reacts with the solvent.

d) N₂ and CH₄. Solubility of N₂ is lower as N₂ is smaller molecule than CH₄ and less hydrated.

NO and C₂H₆ have similar water solubility. NO is more soluble than ethane and form dipole-dipole interactions, but the dispersion forces of ethane and water are stronger than dispersion forces between NO and water as ethane is larger, more polarizable molecule. The sum of all intermolecular interactions is similar for these two gases, leading to the similar water solubility.

NO and O₂. NO is more soluble as it is polar molecule and form stronger intermolecular forces with polar solvent molecules compared to nonpolar O₂ molecule.

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CHEM 205 Lecture Notes - Lecture 5: Covalent Bond, Strong Electrolyte, Sodium Chloride

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