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Solutions

Solutions. What Is A Solution?. Recall from Unit 2 that a sol'n is a homogeneous mixture. Solvent – major component of a solution. Dissolves the solute(s). Solute(s) – minor component(s) of a solution. Active ingredients of a solution. Solution = solvent + solute(s).

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Solutions

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  1. Solutions

  2. What Is A Solution? • Recall from Unit 2 that a sol'n is a homogeneous mixture. • Solvent – major component of a solution. • Dissolves the solute(s). • Solute(s) – minor component(s) of a solution. • Active ingredients of a solution. • Solution = solvent + solute(s)

  3. Some Common Solutions

  4. The Solution Process • 3 things happen when a solute dissolves: • 1. Solute particles separate. • This requires energy to overcome the intermolecular forces holding them together. • 2. Solvent molecules separate. • This also requires energy. • 3. Solvent particles surround solute particles. • Known as “solvation”. • Releases energy.

  5. The Solution Process 1. Particles separate from solute. 2. Solvent molecules move apart to accommodate solute. 3. Solvation

  6. Ions in Solution Solvated cation Solvated anion

  7. The Solution Process

  8. Energy Changes in Solutions • The formation of a solution always involves a temperature change. • Can be a large or small temperature change. • Can get warmer or cooler as solute dissolves. • H = enthalpy (heat) of solution • Energy absorbed or released as a solute dissolves in a solvent. • +H = endothermic sol’n process. • More heat absorbed than released. • Temperature decreases as sol’n is formed. • -H = exothermic sol’n process. • More heat released than absorbed. • Temperature increases as sol’n is formed.

  9. Energy Changes in Solutions

  10. Solubility • Not all substances dissolve in water. • Remember, “like dissolves like”. • Polar solutes tend to dissolve more in polar solvents. • Non-polar solutes tend to dissolve more in non-polar solvents. • Some (but not all) ionic compounds will dissolve in water. • Of those that do, temperature affects how much they dissolve. • Solids usually dissolve more in warm water. • Gases usually dissolve more in cool water.

  11. Solubility • Insoluble – less than 0.1 grams of solute will dissolve in 100 grams of solvent. • BaSO4 is insoluble in water. • Only 0.0002448 grams of BaSO4 will dissolve in 100 grams of water. • Slightly soluble – 0.1 to 1 gram of solute will dissolve in 100 grams of solvent. • Ag2SO4 is slightly soluble in water. • About 0.8 grams of Ag2SO4 will dissolve in 100 grams of water at 20ºC. • Soluble – more than 1 gram of solute will dissolve in 100 grams of solvent. • NaCl is soluble in water. • 35.9 grams of NaCl will dissolve in 100 grams of water at 20ºC.

  12. Solubility Rules • Set of generalizations that describe the solubility of classes of salts. • Not quantitative. • No need to memorize, but you should be familiar with how to use them.

  13. Solubility Rules • The following compounds are soluble in water with exceptions as noted: • Salts containing Group 1A ions (Li+1, Na+1, K+1, etc). • No exceptions. • EX: LiCl, NaOH, and K2SO4 are all soluble in water. • Salts containing the ammonium ion (NH4+1). • No exceptions. • EX: NH4NO3 and (NH4)3PO4 are both soluble in water. • Salts containing the acetate ion (C2H3O2-1). • No exceptions. • EX: NaC2H3O2, Ba(C2H3O2)2, and Al(C2H3O2)3 are all soluble in water.

  14. Solubility Rules • The following compounds are soluble in water with exceptions as noted: • Salts containing the nitrate ion (NO3-1). • No exceptions. • EX: AgNO3, Ba(NO3)2, and Cu(NO3)2 are all soluble in water. • Salts containing chloride (Cl-1), bromide (Br-1), or iodide (I-1) ions. • Except for salts with Ag+1, Pb+2, or Hg2+2 ions. • EX: NaCl, AlBr3, and FeI3 are all soluble in water, but AgCl, PbBr2, and Hg2I2 are insoluble in water.

  15. Solubility Rules • The following compounds are soluble in water with exceptions as noted: • Salts containing the sulfate ion (SO4-2). • Except for salts with Ca+2, Sr+2, Ba+2, or Pb+2 ions. • EX: CuSO4, Fe2(SO4)3, and K2SO4 are all soluble in water, but CaSO4, SrSO4, BaSO4, and PbSO4 are insoluble in water.

  16. Solubility Rules • The following compounds are insoluble in water with exceptions as noted: • Salts containing the carbonate (CO3-2) or phosphate (PO4-3) ions. • Except for salts with Group 1A or NH4+1 ions. • EX: CuCO3 and Mg3(PO4)2 are both insoluble in water, but Na2CO3 and (NH4)3PO4 are soluble in water. • Salts containing the sulfide ion (S-2). • Except for salts with Group 1A, 2A, or NH4+1 ions. • EX: CuS, Fe2S3, and Al2S3 are all insoluble in water, but Na2S, CaS, and (NH4)2S are soluble in water.

  17. Solubility Rules • The following compounds are insoluble in water with exceptions as noted: • Salts containing the hydroxide (OH-1) ion. • Except for salts with Group 1A, Ba+2, Sr+2, or Ca+2 ions. • EX: Ni(OH)2, Al(OH)3, and Be(OH)2 are all insoluble in water, but KOH, Ba(OH)2, and Ca(OH)2 are soluble in water.

  18. Solubility Rules • Use your list of solubility rules to determine whether each of the following salts is soluble or insoluble in water. • NaCl • K2SO4 • CaCO3 • NH4NO3 • Cu3(PO4)2 • AgBr • NaCl is soluble. • K2SO4 is soluble. • CaCO3 is insoluble. • NH4NO3 is soluble. • Cu3(PO4)2 is insoluble. • AgBr is insoluble.

  19. Saturation • Saturated solution • A sol’n containing the max. amt. of solute for a given amt. of solvent at constant temp. and pressure. • If additional solute is added it will not dissolve. • Unsaturated solution • A sol’n that does not contain the max. amt. of solute for a given amt. of solvent. • Additional solute can dissolve in an unsaturated solution. • Supersaturated solution • A sol’n that contains more solute than it can theoretically hold at a given temperature. • Addition of more solute causes the excess solute to precipitate.

  20. Solubility Curves • Solubility curve chart – compares the solubilities of several compounds in water as a function of temperature. • Usually expresses solubility in terms of grams of solute per 100 grams of water.

  21. Solubility Curves • How many grams of KNO3 can dissolve in 100 grams of water at 30ºC? • Answer: About 48 grams.

  22. Solubility Curves • How many grams of KClO3 can dissolve in 100 grams of water at 55ºC? • Answer: About 25 grams.

  23. Solubility Curves • How many grams of NH4Cl can be dissolved in 200 grams of water at 40ºC? • Answer: About 96 grams.

  24. Solubility Curves • A saturated solution of NaNO3 is prepared at 70ºC in 100 grams of water. If the temperature is lowered to 40ºC, how many grams of NaNO3 will precipitate? • Answer: About 30 grams will precipitate out.

  25. Solubility Curves • If 35 grams of NH4Cl are dissolved in 100 grams of water at 30ºC, is the solution unsaturated, saturated, or supersaturated? • Answer: The solution is unsaturated.

  26. Solubilities of Gases • Henry’s Law – The solubility of a gas in a liquid increases as the pressure above the liquid increases. • Explains decompression sickness (the “bends”). • Nitrogen is forced to dissolve in scuba divers’ blood by high pressure. • If the diver ascends too quickly, the nitrogen bubbles come out of solution and form painful and possibly fatal gas embolisms.

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