Chapter 4 Lecture- Solution Stoich
- 1. Solutions: Homogeneous mixtures of two or more pure substances. The solvent is present in greatest abundance. All other substances are solutes .
- 2. Dissociation When an ionic substance dissolves in water, the solvent pulls the individual ions from the crystal and solvates them. This process is called dissociation .
- 3. Electrolytes Substances that dissociate into ions when dissolved in water. A nonelectrolyte may dissolve in water, but it does not dissociate into ions when it does so.
- 4. Electrolytes and Nonelectrolytes Soluble ionic compounds tend to be electrolytes.
- 5. Electrolytes and Nonelectrolytes Molecular compounds tend to be nonelectrolytes, except for acids and bases.
- 6. Electrolytes A strong electrolyte dissociates completely when dissolved in water. A weak electrolyte only dissociates partially when dissolved in water.
- 7. Strong Electrolytes Are… Strong acids
- 8. Strong Electrolytes Are… Strong acids Strong bases
- 9. Strong Electrolytes Are… Strong acids Strong bases Soluble ionic salts
- 10. Answers: C 6 H 12 O 6 (nonelectrolyte) < HC 2 H 3 O 2 (weak electrolyte, existing mainly in the form of molecules with few ions) < NaC 2 H 3 O 2 (strong electrolyte that provides two ions, and (strong electrolyte that provides three ions, Ca 2+ and 2 NO 3 – PRACTICE EXERCISE Consider solutions in which 0.1 mol of each of the following compounds is dissolved in 1 L of water: Ca(NO 3 ) 2 (calcium nitrate), C 6 H 12 O 6 (glucose), NaC 2 H 3 O 2 (sodium acetate), and HC 2 H 3 O 2 (acetic acid). Rank the solutions in order of increasing electrical conductivity, based on the fact that the greater the number of ions in solution, the greater the conductivity.
- 11. Precipitation Reactions When one mixes ions that form compounds that are insoluble (as could be predicted by the solubility guidelines), a precipitate is formed.
- 12. PRACTICE EXERCISE Classify the following compounds as soluble or insoluble in water: (a) cobalt(II) hydroxide, (b) barium nitrate, (c) ammonium phosphate. Answers: (a) insoluble, (b) soluble, (c) soluble
- 13. PRACTICE EXERCISE What compound precipitates when solutions of Fe 2 (SO 4 ) 3 and LiOH are mixed? (b) Write a balanced equation for the reaction. (c) Will a precipitate form when solutions of Ba(NO 3 ) 2 and KOH are mixed? (c) no (both possible products are water soluble)
- 14. Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means “to transpose” AgNO 3 ( aq ) + KCl ( aq ) AgCl ( s ) + KNO 3 ( aq )
- 15. Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means “to transpose” It appears the ions in the reactant compounds exchange, or transpose, ions Ag NO 3 ( aq ) + K Cl ( aq ) AgCl ( s ) + KNO 3 ( aq )
- 16. Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means “to transpose” It appears the ions in the reactant compounds exchange, or transpose, ions Ag NO 3 ( aq ) + K Cl ( aq ) AgCl ( s ) + KNO 3 ( aq )
- 17. Solution Chemistry It is helpful to pay attention to exactly what species are present in a reaction mixture (i.e., solid, liquid, gas, aqueous solution). If we are to understand reactivity, we must be aware of just what is changing during the course of a reaction.
- 18. Molecular Equation The molecular equation lists the reactants and products in their molecular form. AgNO 3 ( aq ) + KCl ( aq ) AgCl ( s ) + KNO 3 ( aq )
- 19. Ionic Equation In the ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions. This more accurately reflects the species that are found in the reaction mixture. Ag + ( aq ) + NO 3 - ( aq ) + K + ( aq ) + Cl - ( aq ) AgCl ( s ) + K + ( aq ) + NO 3 - ( aq )
- 20. Net Ionic Equation To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. Ag + (aq) + NO 3 - ( aq ) + K + (aq) + Cl - ( aq ) AgCl ( s ) + K + (aq) + NO 3 - ( aq )
- 21. Net Ionic Equation To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. The only things left in the equation are those things that change (i.e., react) during the course of the reaction. Ag + (aq) + Cl - ( aq ) AgCl ( s )
- 22. Net Ionic Equation To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. The only things left in the equation are those things that change (i.e., react) during the course of the reaction. Those things that didn’t change (and were deleted from the net ionic equation) are called spectator ions . Ag + (aq) + NO 3 - ( aq ) + K + (aq) + Cl - ( aq ) AgCl ( s ) + K + (aq) + NO 3 - ( aq )
- 23. Writing Net Ionic Equations Write a balanced molecular equation. Dissociate all strong electrolytes. Cross out anything that remains unchanged from the left side to the right side of the equation. Write the net ionic equation with the species that remain.
- 24. PRACTICE EXERCISE Write the net ionic equation for the precipitation reaction that occurs when aqueous solutions of silver nitrate and potassium phosphate are mixed.
- 25. Acids: Substances that increase the concentration of H + when dissolved in water (Arrhenius). Proton donors (Brønsted – Lowry).
- 26. Acids There are only seven strong acids: Hydrochloric (HCl) Hydrobromic (HBr) Hydroiodic (HI) Nitric (HNO 3 ) Sulfuric (H 2 SO 4 ) Chloric (HClO 3 ) Perchloric (HClO 4 )
- 27. Bases: Substances that increase the concentration of OH − when dissolved in water (Arrhenius). Proton acceptors (Brønsted – Lowry).
- 28. Bases The strong bases are the soluble salts of hydroxide ion: Alkali metals Calcium Strontium Barium
- 29. Acid-Base Reactions In an acid-base reaction, the acid donates a proton (H + ) to the base.
- 30. Neutralization Reactions Generally, when solutions of an acid and a base are combined, the products are a salt and water. HCl ( aq ) + NaOH ( aq ) NaCl ( aq ) + H 2 O ( l )
- 31. Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is… HCl ( aq ) + NaOH ( aq ) NaCl ( aq ) + H 2 O ( l ) H + ( aq ) + Cl - ( aq ) + Na + ( aq ) + OH - ( aq ) Na + ( aq ) + Cl - ( aq ) + H 2 O ( l )
- 32. Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is… HCl ( aq ) + NaOH ( aq ) NaCl ( aq ) + H 2 O ( l ) H + ( aq ) + Cl - ( aq ) + Na + ( aq ) + OH - ( aq ) Na + ( aq ) + Cl - ( aq ) + H 2 O ( l ) H + ( aq ) + Cl - ( aq) + Na + ( aq ) + OH - ( aq ) Na + ( aq ) + Cl - ( aq ) + H 2 O ( l )
- 33. PRACTICE EXERCISE (a) Write a balanced molecular equation for the reaction of carbonic acid (H 2 CO 3 ) and potassium hydroxide (KOH). (b) Write the net ionic equation for this reaction. (H 2 SO 3 is a weak acid and therefore a weak electrolyte, whereas KOH, a strong base, and K 2 CO 3 , an ionic compound, are strong electrolytes.)
- 34. Gas-Forming Reactions These metathesis reactions do not give the product expected. The expected product decomposes to give a gaseous product (CO 2 or SO 2 ). CaCO 3 ( s ) + HCl ( aq ) CaCl 2 ( aq ) + CO 2 ( g ) + H 2 O ( l ) NaHCO 3 ( aq ) + HBr ( aq ) NaBr ( aq ) + CO 2 ( g ) + H 2 O ( l ) SrSO 3 ( s ) + 2 HI ( aq ) SrI 2 ( aq ) + SO 2 ( g ) + H 2 O ( l )
- 35. Gas-Forming Reactions This reaction gives the predicted product, but you had better carry it out in the hood, or you will be very unpopular! Just as in the previous examples, a gas is formed as a product of this reaction: Na 2 S ( aq ) + H 2 SO 4 ( aq ) Na 2 SO 4 ( aq ) + H 2 S ( g )
- 36. BELLWORK Write the molecular equation, the complete ionic equation, and the net ionic equation for the reaction that occurs when the following are mixed. Identify the spectator ions. HF(aq) + NaOH(aq)
- 37. Oxidation-Reduction Reactions An oxidation occurs when an atom or ion loses electrons. A reduction occurs when an atom or ion gains electrons.
- 38. Oxidation-Reduction Reactions One cannot occur without the other.
- 39. Oxidation Numbers To determine if an oxidation-reduction reaction has occurred, we assign an oxidation number to each element in a neutral compound or charged entity.
- 40. Oxidation Numbers Elements in their elemental form have an oxidation number of 0. The oxidation number of a monatomic ion is the same as its charge.
- 41. Oxidation Numbers Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions. Oxygen has an oxidation number of − 2, except in the peroxide ion in which it has an oxidation number of − 1. Hydrogen is − 1 when bonded to a metal, +1 when bonded to a nonmetal.
- 42. Oxidation Numbers Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions. Fluorine always has an oxidation number of − 1. The other halogens have an oxidation number of − 1 when they are negative; they can have positive oxidation numbers, however, most notably in oxyanions.
- 43. Oxidation Numbers The sum of the oxidation numbers in a neutral compound is 0. The sum of the oxidation numbers in a polyatomic ion is the charge on the ion.
- 45. Displacement Reactions In displacement reactions, ions oxidize an element. The ions, then, are reduced.
- 46. Displacement Reactions In this reaction, silver ions oxidize copper metal. Cu ( s ) + 2 Ag + ( aq ) Cu 2+ ( aq ) + 2 Ag ( s )
- 47. Displacement Reactions The reverse reaction, however, does not occur. Cu 2+ ( aq ) + 2 Ag ( s ) Cu ( s ) + 2 Ag + ( aq ) x
- 48. Activity Series
- 49. Bellwork Question4-style #1 a)A solution of ethanoic (acetic) acid is added to a solution of barium hydroxide. b)Explain why a mixture of equal volumes of equimolar solutions of acetic acid and barium hydroxide is basic.
- 50. Molarity Two solutions can contain the same compounds but be quite different because the proportions of those compounds are different. Molarity is one way to measure the concentration of a solution. moles of solute volume of solution in liters Molarity ( M ) =
- 52. Dilution
- 53. Answer: 0.278 M SAMPLE EXERCISE 4.11 PRACTICE EXERCISE Calculate the molarity of a solution made by dissolving 5.00 g of glucose (C 6 H 12 O 6 ) in sufficient water to form exactly 100 mL of solution.
- 54. PRACTICE EXERCISE What is the molar concentration of K + ions in a 0.015 M solution of potassium carbonate? Answer: 0.030 M K +
- 55. PRACTICE EXERCISE (a) How many grams of Na 2 SO 4 are there in 15 mL of 0.50 M Na 2 SO 4 ? (b) How many milliliters of 0.50 M Na 2 SO 4 solution are needed to provide 0.038 mol of this salt? Answers: (a) 1.1 g, (b) 76 mL
- 56. PRACTICE EXERCISE (a) What volume of 2.50 M lead(II)nitrate solution contains 0.0500 mol of Pb 2+ ? (b) How many milliliters of 5.0 M K 2 Cr 2 O 7 solution must be diluted to prepare 250 mL of 0.10 M solution? (c) If 10.0 mL of a 10.0 M stock solution of NaOH is diluted to 250 mL, what is the concentration of the resulting stock solution? Answers: (a) 0.0200 L = 20.0 mL, (b) 5.0 mL, (c) 0.40 M
- 57. Using Molarities in Stoichiometric Calculations
- 58. PRACTICE EXERCISE (a) How many grams of NaOH are needed to neutralize 20.0 mL of 0.150 M H 2 SO 4 solution? (b) How many liters of 0.500 M HCl( aq ) are needed to react completely with 0.100 mol of Pb(NO 3 ) 2 ( aq ), forming a precipitate of PbCl 2 ( s )? Answers: (a) 0.240 g, (b) 0.400 L
- 59. Titration The analytical technique in which one can calculate the concentration of a solute in a solution.
- 60. Titration
- 61. PRACTICE EXERCISE What is the molarity of an NaOH solution if 48.0 mL is needed to neutralize 35.0 mL of 0.144 M H 2 SO 4 ? Answers: 0.210 M