Vocabulary In SOLUTION we need to define the - SOLVENT the component whose physical state is preserved when solution forms SOLUTE the other solution component.
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Vocabulary In SOLUTION we need to define the - SOLVENT the component whose physical state is preserved when solution forms SOLUTE the other solution component The CONCENTRATION is most often expressed by chemists as MOLARITY. Other common expressions of concentration are w/w, vol/vol, and normality.
1.0 L of water was used to make 1.0 L of solution. Notice the water left over. CCR, page 206
PROBLEM: Dissolve 5.00 g of NiCl 2 6 H 2 O in enough water to make 250 mL of solution. Calculate molarity of the solution and the concentration of each of the ions.
Problem: What mass of oxalic acid, H 2 C 2 O 4, is required to make 250. mL of a 0.0500 M solution?
PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do?
Zinc reacts with acids to produce H 2 gas.Zinc reacts with acids to produce H 2 gas. Have 10.0 g of ZnHave 10.0 g of Zn What volume of 2.50 M HCl is needed to convert the Zn completely? What volume of 2.50 M HCl is needed to convert the Zn completely? SOLUTION STOICHIOMETRY Section 5.10
Zinc reacts with acids to produce H 2 gas. If you have 10.0 g of Zn, what volume of 2.50 M HCl is needed to convert the Zn completely?
Non-Electrolytes – they dissolve, but won’t conduct electricity. These are generally polar solids capable of forming hydrogen bonds –Sugar, ethanol, ethylene glycol Strong Electrolytes – Completely dissociates, conducts electricity well – most ionic solids and strong acids Weak Electrolytes – Dissolve, ionize to a small extent, conducts electricity weakly. Weak acids, such as Acetic acid, ionize only to a small extent, so it are a weak electrolyte. CH 3 CO 2 H (aq) → CH 3 CO 2 - (aq) +H + (aq) Aqueous Solutions
Water Solubility of Ionic Compounds If one ion from the “Soluble Compound” list is present in a compound, the compound is water soluble.
There are three ways to write reactions in aqueous solutions. Molecular equation: Show all reactants & products in molecular or ionic form Total ionic equation: Show the ions and molecules as they exist in solution Net ionic equation: Shows ions that participate in reaction and removes spectator ions. Spectator ions do not participate in the reaction.
Net Ionic Equations Mg (s) + 2HCl (aq) → H 2(g) + MgCl 2(aq) The molecular formula above can be written as the total ionic formula Mg (s) + 2H + (aq) + 2Cl - (aq) → H 2(g) + Mg 2+ (aq) + 2Cl - (aq) The two Cl - ions are SPECTATOR IONS — they do not participate. Could have used NO 3- for the spectator ion as salts of nitrates are all soluble. By leaving out the spectator ions out you get the net ionic reaction Mg (s) + 2 H + (aq) ---> H 2(g) + Mg 2+ (aq)
HNO 3 A Brönsted-Lowry Acid → H + in water ACIDS Table 5.2 Strong Brönsted-Lowry acids are strong electrolytes Strong Brönsted-Lowry acids are strong electrolytes HClhydrochloric H 2 SO 4 sulfuric HClO 4 perchloric HNO 3 nitric Weak Brönsted-Lowry acids are weak electrolytes CH 3 CO 2 H acetic acid (CH 3 COOH) H 2 CO 3 carbonic acid H 3 PO 4 phosphoric acid HF hydrofluoric acid Acetic acid Carbonic Acid
Ammonia, NH 3 a Ammonia, NH 3 an Important weak Base Brönsted-LowryBase → OH - in water Brönsted-Lowry Base → OH - in water BASES Table 5.2 NaOH(aq) → Na+(aq) + OH-(aq) NaOH is a strong base
ACIDS Nonmetal oxides can be acids CO 2(aq) + H 2 O (l) → H 2 CO 3(aq) SO 3(aq) + H 2 O (l) → H 2 SO 4(aq) NO 2(aq) + H 2 O (l) → HNO 3(aq) Acid Rain is an example of nonmetal oxides behaving as acids. This process can result from burning coal and oil. Metal oxides can be bases CaO (s) +H 2 O (l) → Ca(OH) 2(aq) CaO in water. Phenolphthalein indicator shows a of calcium oxide solution is basic. BASES
A brief history of Acid-Base Identification Systems SystemAcid (HCl)Base (NaOH) Arrhenius Brönsted- Lowry Lewis
pH, a Concentration Scale pH: a way to express acidity -- the concentration of H + in solution. Low pH: high [H + ] High pH: low [H + ] Acidic solutionpH < 7 Neutral pH = 7 Neutral pH = 7 Basic solution pH > 7 Basic solution pH > 7 Acidic solutionpH < 7 Neutral pH = 7 Neutral pH = 7 Basic solution pH > 7 Basic solution pH > 7
The pH Scale pH = log (1/ [H + ]) = - log [H + ] In a neutral solution, [H + ] = [OH - ] = 1.00 x 10 -7 M at 25 o C pH = - log [H + ] = If the [H + ] of soda is 1.6 x 10 -3 M, the pH is ____. If the pH of Coke is 3.12, it is _____.
ACID-BASE REACTIONS Titrations H 2 C 2 O 4(aq) + 2 NaOH (aq) → Na 2 C 2 O 4(aq) + 2 H 2 O (l) acid base acid base Carry out this reaction using a TITRATION. Oxalic acid, H 2 C 2 O 4
Titration 1. Add solution from the buret. 2. Reagent (base) reacts with compound (acid) in solution in the flask. 3. Indicator shows when exact stoichiometric reaction has occurred. 4. Net ionic equation H + + OH - --> H 2 O H + + OH - --> H 2 O 5. At equivalence point moles H + = moles OH - moles H + = moles OH -
PROBLEM: Standardize a solution of NaOH — i.e., accurately determine its concentration. PROBLEM: Standardize a solution of NaOH — i.e., accurately determine its concentration. 1.065 g of H 2 C 2 O 4 (oxalic acid) requires 35.62 mL of NaOH for titration to an equivalence point. What is the concentration of the NaOH?
PROBLEM : Use standardized NaOH to determine the amount of an acid in an unknown. Apples contain malic acid, C 4 H 6 O 5. 76.80 g of apple requires 34.56 mL of 0.663 M NaOH for titration. What is weight % of malic acid? C 4 H 6 O 5(aq) + 2NaOH (aq) → Na 2 C 4 H 4 O 5(aq) + 2 H 2 O (l)
Types of Reactions: 1.Combination Reactions More than one reactant, one product 2.Decomposition Reactions Single reactant, more than one product 3.Displacement Reactions One element displaces another from a compound 4.Redox – Oxidation Reduction Reactions Oxidation numbers of some elements change; at least one element must increase and one must decrease in oxidation number. 5.Metathesis Reactions - Exchange Reactions Precipitation: products include an insoluble substance which precipitates from solution as a solid Acid-base neutralization: product is a salt and water Gas formation – primarily the reaction of metal carbonates
OXIDATION NUMBERS NH 3 ClO - H 3 PO 4 MnO 4 - Cr 2 O 7 2-
Recognizing a Redox Reaction 2 Al (s) + 3 Cu 2+ (aq) → 2 Al 3+ (aq) + 3 Cu (s)
Oxidation-Reduction Reactions Thermite reaction Fe 2 O 3(s) + 2Al (s) → 2 Fe (s) + Al 2 O 3(s) 2Al (s) + 3Cu 2+ (aq) → 2Al 3+ (aq) + 3Cu (s) 2 H 2(g) + O 2(g) → 2H 2 O (l) In all reactions if something has been oxidized then something has also been reduced. Redox reactions are characterized by ELECTRON TRANSFER between an electron donor and electron acceptor. Transfer leads to 1. increase in oxidation number of some element = OXIDATION 2.decrease in oxidation number of some element = REDUCTION
Chemical Reactions in Water Metathesis EXCHANGE REACTIONSEXCHANGE REACTIONS Precipitation Pb(NO 3 ) 2(aq) + 2 KI (aq) → PbI 2(s) + 2KNO 3(aq) Pb2+(aq) + 2 I-(aq) → PbI2(s) Neutralization: NaOH (aq) + HCl (aq) → NaCl (aq) + H 2 O (l) OH - (aq) + H + (aq) → H 2 O (lq) Gas Formation MgCO 3(s) + 2 (aq) → 2Mg(Cl) 2(aq) + H 2 O (l) MgCO 3(s) + 2HCl (aq) → 2Mg(Cl) 2(aq) + H 2 O (l) + CO 2(g) The anions exchange places between cations.