Unit 6: Solutions and Solubility

1. Unit 6: Solutions and Solubility Day 2 Solution Enthalpies

2. Unit 6: Solutions and Solubility The new salt water fish tank in room 406 must be closely monitored and have salinity and pH levels that fall within very strict guidelines. As of yesterday afternoon, the NO2- concentration was 0.25 ppm, or 5.41x10-6 M. • What is the molality of nitrite ion in the tank? • What is the mole fraction and weight %?

3. Unit 6: Solutions and Solubility • Enthalpy of solution It may not seem like it, but dissolving something can be exothermic or endothermic, just like chemical reactions • Would you expect the dissolving of a salt to require energy (endothermic) or to yield energy (exothermic)

4. Unit 6: Solutions and Solubility • Enthalpy of solution It may not seem like it, but dissolving something can be exothermic or endothermic, just like chemical reactions • Would you expect the dissolving of a salt to require energy (endothermic) or to yield energy (exothermic) Chunks of solute + H H - + - + O + - + - - - + - +

5. Unit 6: Solutions and Solubility • Enthalpy of solution It may not seem like it, but dissolving something can be exothermic or endothermic, just like chemical reactions • Would you expect the dissolving of a salt to require energy (endothermic) or to yield energy (exothermic) Chunks of solute + H H - + - + O + - + - - - + - +

6. Unit 6: Solutions and Solubility • Enthalpy of solution It may not seem like it, but dissolving something can be exothermic or endothermic, just like chemical reactions • Would you expect the dissolving of a salt to require energy (endothermic) or to yield energy (exothermic) Chunks of solute + H H - + - + O + - + - - - + - +

7. Unit 6: Solutions and Solubility • Enthalpy of solution It may not seem like it, but dissolving something can be exothermic or endothermic, just like chemical reactions • Would you expect the dissolving of a salt to require energy (endothermic) or to yield energy (exothermic) Chunks of solute + H H - + - + O + - + - - - + - +

8. Unit 6: Solutions and Solubility • Enthalpy of solution It may not seem like it, but dissolving something can be exothermic or endothermic, just like chemical reactions • Would you expect the dissolving of a salt to require energy (endothermic) or to yield energy (exothermic) Chunks of solute - + - + + H H O + - + - - - + - +

9. Unit 6: Solutions and Solubility • Enthalpy of solution It may not seem like it, but dissolving something can be exothermic or endothermic, just like chemical reactions • Would you expect the dissolving of a salt to require energy (endothermic) or to yield energy (exothermic) Chunks of solute - + - + + H H + - + - O - + - + -

10. Unit 6: Solutions and Solubility • Enthalpy of solution It may not seem like it, but dissolving something can be exothermic or endothermic, just like chemical reactions • Would you expect the dissolving of a salt to require energy (endothermic) or to yield energy (exothermic) Chunks of solute - + - + + H H - + - + O - + - + -

11. Unit 6: Solutions and Solubility • Enthalpy of solution It may not seem like it, but dissolving something can be exothermic or endothermic, just like chemical reactions • Would you expect the dissolving of a salt to require energy (endothermic) or to yield energy (exothermic) Chunks of solute - + - + + H H - O + - + - - + - +

12. Unit 6: Solutions and Solubility • Enthalpy of solution It may not seem like it, but dissolving something can be exothermic or endothermic, just like chemical reactions • Would you expect the dissolving of a salt to require energy (endothermic) or to yield energy (exothermic) Chunks of solute + H H - - + - + O + - + - - + - +

13. Unit 6: Solutions and Solubility • Enthalpy of solution It may not seem like it, but dissolving something can be exothermic or endothermic, just like chemical reactions • Would you expect the dissolving of a salt to require energy (endothermic) or to yield energy (exothermic) + Chunks of solute H H - O - + - + - + - + - + - +

14. Unit 6: Solutions and Solubility • Enthalpy of solution It may not seem like it, but dissolving something can be exothermic or endothermic, just like chemical reactions • Would you expect the dissolving of a salt to require energy (endothermic) or to yield energy (exothermic) • Energy model for the dissolving of KF • Important points…

15. Unit 6: Solutions and Solubility • Calculating Enthalpy of Solution from data: Solution Enthalpies can be calculated using enthalpies of formation just like with reactions. • Determine the enthalpy of solution for NH4NO3, the compound found in cold packs.

16. Unit 6: Solutions and Solubility • To make some of your own anti-freeze, you add 1.2 kg of ethylene glycol, HOCH2CH2OH, to 4.0 kg of water. • What are the mole fraction, molality and weight percent of ethylene glycol in solution? MolalityWeight %Mole fraction NaI 0.35 C2H5OH 2.5 C12H22O11 0.35

17. Unit 6: Solutions and Solubility • Units of Concentration • Different concentration units are useful for different things in chemistry so you must be familiar with all of them. • Molarity • Useful for stoichiometry • Molality • Useful for colligative property calculations • Mole fraction • Weight percent • Consumer products • Parts per million/billion/etc • Naturally occurring solutions that are typically very dilute