CHEM 120 Lecture Notes - Lecture 12: Colligative Properties, Freezing-Point Depression, Sodium Chloride

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Enthalpy: overall enthalpy change can be +, -, or close to zero, dissociate solute (endo), dissociate solvent (endo), mix solvent and solute (exo) If dissolution endothermic, recrystallization must be exo (heat packs) Increasing pressure increases rate of gas condensation into liquid increase [c: solubility of co2 in water is high under high pressure, opening bottle relieves pressure, solubility decreases, bubbles of n2 killed julius kroehl. The bends (decompression sickness: gas at high pressure becomes dissolved in the blood and tissues, at lower pressure, solubility is lower and gas comes out of solution to form bubbles. Temp of boiling wine, starts below 100 and increases (ethanol is more volatile than water so lower boiling point than water: the vapors enriched in ethanol, at wine boils, content decreases and so bp increases. Freezing point depression & boiling point elevation: dissolved non-volatile solutes: lower freezing point of solvent.

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D. 1. Silver chloride is not soluble in water. What are the relative strengths of the intermolecular forces between Ag and Ciions and water molecules as compared to the intermolecular forces between water molecules and the forces that hold the silver chloride as a solid? a. The ionic attractions are stronger than the polar covalent bonds between the H' and O ions of the b. The ionic attractions are weaker than the intermolecular forces between the Ag' and Cr ions and water c. The ionic attractions are stronger than the intermolecular forces between the Ag' and Cr ions and water d. The ionic attractions are the same as the intermolecular forces between the Ag and CI ions and water water molecules. molecules. molecules molecules 2. The value of AHsotn for a water soluble compound is +34 kJ moÄ¾1. Which value for this compound would be numerically larger, its lattice energy or its hydration energy? Select the single best answer. step. b. The lattice energy, because it is the endothermic step c. The hydration energy, because it is the exothermic step. d. The lattice energy, because it is the exothermic step. 3, which of the following are reasons why the value of ì¨,on for a gas such as CO2, dissolving in water, is negative? a. When a gas dissolves in a liquid, there is no endothermic step as with the lattice energy of a solid. b. When a gas dissolves in a liquid, there is only an exothermic step as with the lattice energy of a solid. c. The only enthalpy change is the one associated with hydration, and this is always positive. d. The only enthalpy change is the one associated with hydration, and this is always negative. e. When a gas dissolves in a liquid the lattice energy is always higher than the hydration energy, making the net enthalpy always negative. 4. Why is ammonia so much more soluble in water than is nitrogen? a. The triple bond in nitrogen prevents it from dissolving in water. b. Nitrogen has only London forces, while both water and ammonia form hydrogen bonds. c. The molar mass of nitrogen is much larger than the molar mass of ammonia, which reduces its solubility. d. Diatomic molecules are never soluble in water s which agueous solution, if either, is likely to have the highÏr boiling point 50 m Nal or en-Na e au

1. Consider the unbalanced equation for the reaction of solid lead with a silver nitrate solution.

_____Pb (s) + ______AgNO3 (ac) â ______Pb(NO3)2 (ac) + _______Ag (s)

a. Balance the equation.

b. How many moles of silver nitrate are required to react completely with 9.3 mol of lead?

c. How many moles of silver, Ag, are formed by the complete reaction of 28.4 mol of Pb?

2. For the following reaction: _____CaO (s) + _____CO2 (g) â _____CaCO3 (s), Calculate how many grams of CaCO3, are formed when 2.4 g of CaO Do they react completely with CO2?

3. For the following reaction: 2 Li (s) + F2 (g) â 2 LiF (s), find the reagent limiting with the amounts of 1.0 mol of Li and 1.0 mol of F2.

4. For the next reaction, determine the limiting reagent, calculate the yield Theoretical product in grams with 5.5 g of Al and 19.8 g of Cl2.

2 Al (s) + 3 Cl2 (g) â 2 AlCl3 (s)

5. Consider the reaction between NiS2 and O2:

2 NiS2 (s) + 5 O2 (g) â 2 NiO (s) + 4 SO2 (g)

When 11.2 g of NiS2 react with 5.43 g of O2, 4.86 g of NiO are obtained. Determine the limiting reagent, the theoretical yield of NiO and the% yield for the reaction.

6. How many atoms of mercury are in 5.8 mol of mercury?

7. Complete the following table:

Element Moles Mass Number of molecules

8. How many grams of sodium are there in 1.00 g of each of the following compounds?

a. Na3PO4

b. NaC7H5O2

c. Na2C6H6O7

9. A sample of 4.78 g of aluminum reacts completely with oxygen to form 6.67 g of aluminum oxide. Use the data to calculate the percent of composition by mass.

10. Citric acid, the compound responsible for the bitter taste in lemons, has the following composition: C - 37.51%

H - 4.40%

O - 58.29%

Calculate the empirical formula.

11. A compound containing phosphorus and oxygen has a molar mass of 219.9 g / mol and an empirical formula of P2O3. Find the molecular formula of compound.

12. It is a term used in chemistry, to describe a system in which a

or more substances, are mixed or dissolved homogeneously in another

substance.

a. Mixture

b. Solution

c. Compound

d. None of the above

13. It is the component that is in a solution, in smaller quantity.

a. Solution

b. Solvent

c. Solvent

d. Soluto

14. It is the component that is in a solution in greater quantity.

a. Solution

b. Solvent

c. Solvent

d. The answers b and c are correct.

15. The quantitative expression of the dissolved amount of solute in a quantity determined solvent is known as:

a. Solution

b. Volume

c. Concentration

d. Stoichiometry

16.Express the moles of solute among the liters of solution

a. Molality

b. Molarity

c. % weight by volume

d. % weight by weight

17.Express the moles of solute between kg of solvent

a. Molarity

b. ppm

c. ppt

d. Molality

18. What is the molarity of a solution prepared by dissolving 7.50 g of nitrate of magnesium, Mg (NO3) 2 in enough water to prepare 25.0 mL of solution?

a. 10.3 M

b. 5.6 M

c. 6.5 M

d. 2.03 M

19. How many grams of sodium chloride, NaCl are needed to prepare 125 mL of 0.037 M NaCl solution

a. 1.021 M

b. 0.268 M

c. 0.201 M

d. 0.500 M

20. Calculate the molality of a solution containing 12.5 g of ethylene glycol (C2H6O2) dissolved in 135 g of water.

21. A solution of ethylene glycol contains 21.2 g of ethylene glycol (C2H6O2) in 85.4 mL of water. Calculate the freezing point and the boiling point of the solution. (Assume the water density is 1.00 g / mL)

22. At what volume should you dilute 75 mL of a 10.0 M solution of H2SO4 to obtain a 1.75 M solution of H2SO4.

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 120 Lecture Notes - Lecture 12: Colligative Properties, Freezing-Point Depression, Sodium Chloride

CHEM 120 Full Course Notes

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