1. Aqueous Reactions and Solution Stoichiometry Chapter 4 BLB 12 th

2. 4.1 General Properties of Aqueous Solutions  Solution – homogeneous mixture (ch. 13)  Solvent – dissolving medium; aq-water  Solute – dissolved substance Electrolytic Properties  Electrolyte – a substance whose aqueous solution contains ions; conducts electricity  Nonelectrolyte – substance that does not form ions in solution

3. Aqueous Solutions, cont. Ionic Compounds in Water  Ionic solids dissociate (or ionize) into ions as they dissolve.  hydration – process of dissolving an ionic substance in water  solvation – dissolving in any solvent; dissolution Why? Water is polar.

4. Polarity of molecules  Electrons are shared unequally.  Results in partial charges (δ), and a…  Dipole moment

5. Hydration of NaCl(s)

6. How many ions does an ionic compound produce when it dissociates? KCl, MgCl 2, or K 2 SO 4 ?

7. Aqueous Solutions, cont. Molecular Compounds in Water  nonelectrolytes – contain only molecules (no ions); do not dissociate; do not conduct electricity; may dissolve in water  Most molecular compounds are nonelectrolytes.  Some may have strong interaction with water (alcohols).  Some may dissociate (acids).

8. Methanol (CH 3 OH) in water

9. Aqueous Solutions, cont. Strong and weak electrolytes – depend on the extent of dissociation Strong – completely dissociate into ions - all water-soluble ionic compounds, strong acids & bases Weak – remain mostly as neutral molecules and produce very few ions; establish chemical equilibrium - weak acids (like acetic acid) and weak bases (like amines); water Note: strong doesn’t mean soluble and vv.

10. 4.2 Precipitation Reactions  Marked by the formation of an insoluble product (precipitate)  Solubility – amount of solute that can be dissolved in a given amount of solvent at a certain temperature; g/100g or g/L or mol/L  Insoluble – solubility < 0.01 mol/L  Solubility Rules – Table 4.1, p. 121  Metathesis (or exchange) reactions

11. Note: All common compounds of Group I metals and NH 4 + are soluble in water.

12. Metathesis (or exchange) reactions Molecular: BaCl 2 (aq) + Na 2 SO 4 (aq) → 2 NaCl(aq) + BaSO 4 (s) Complete ionic: Net ionic:

13. Metathesis (or exchange) reactions Molecular: NaI(aq) + Pb(NO 3 ) 2 (aq) → Complete ionic: Net ionic:

14. Metathesis (or exchange) reactions Molecular: NaOH(aq) + Co(NO 3 ) 2 (aq) → Complete ionic: Net ionic:

15. 4.3 Acids, Bases, and Neutralization Reactions  Involve H +  Acid – H + donor Base – H + acceptor  Neutralization: acid + base → salt + water HCl + NaOH → NaCl + H 2 O

18. 4.3 Acids, Bases, and Neutralization Reactions Strong and Weak  Strong – completely dissociate  Weak – only partially ionize  Neutralization: acid + base → salt + water HCl + NaOH → NaCl + H 2 O

22. 4.4 Oxidation-Reduction (Redox) Reactions  Involve transfer of e¯  Oxidation – loss of e¯ Reduction – gain of e¯  Oxidation number – a “charge” assigned to an atom to keep track of electrons transferred during redox  Displacement reaction – ion in solution is replaced through oxidation of an element.

25. 4.5 Concentrations of Solutions  Molarity (M) – mole solute/L solution M V = mol  Dilution – adding solvent to decrease concentration M 1 V 1 = M 2 V 2 mol 1 = mol 2 ; only volume changes

26. Calculate the concentration (in M) if 2.50 g (NH 4 ) 2 SO 4 is dissolved in enough water to form 250 mL of solution.

27. How many grams of K 2 Cr 2 O 7 are needed to make 50.0 mL of 0.850 M solution?

28. Ion Concentration: 0.850 M K 2 Cr 2 O 7  Concentration (M) of Cr 2 O 7 2- ?  Concentration (M) of K + ?

29. What volume (in mL) of 6.0 M HNO 3 is needed to make 250 mL of 1.0 M HNO 3 ?

30. 4.6 Solution Stoichiometry and Chemical Analysis  Use M and volume to obtain moles  Titration – process used to determine the concentration of a solution (p. 145 ff) Standard solution – one of precisely known concentration Analyte – solution of unknown concentration

31. Stoichiometry Overview, p. 144