Types of Chemical Reactions And Solution Stoichiometry Chapter

Types of Chemical Reactions And Solution Stoichiometry Chapter 4

Water, The Common Solvent Hydration of an ionic compound will occur when the partial positive end of a water becomes attracted to the anions in the compound; likewise for the partial negative center of the water and the cations. Solubility depends on the strength of the intermolecular attractions between the ions and water, as well as the intramolecular attractions of the cations and anions of the compound. NH 4 NO 3(s) NH 4+(aq) + NO 3 -(aq)

What can dissolve in H 2 O? n Soluble n n Alcohols ex: C 2 H 5 OH Sugars ex: C 6 H 12 O 6 Ionic compounds ex: Na. Cl, KOH, Li. Br Insoluble n n n Fats ex: bacon grease Oils ex: cooking oil Non-Polar Substances ex: turpentine Because of intermolecular forces: the OH group on the sugars and alcohols is particularly attractive to a water molecule. Generally speaking: “Like Dissolves Like”

Strong and Weak Electrolytes n n Solute + Solvent = Solution Strong electrolytes conduct electricity Weak electrolytes barely conduct electricity Conductivity depends upon ionization

n Strong Electrolytes n n n Soluble salts Strong acids Strong bases All of these dissociate completely in water. HCl H+ + Cl- n Weak Electrolytes n n Weak acids Weak bases All of these partially dissociate in water HC 2 H 3 O 2 H + + C 2 H 3 O 2 Na. OH Na+ + OHNon-Electrolytes are completely molecular substances in water (not even a little dissociation); Non polar substances.

Composition of Solutions n n Concentration is measured in molarity, molality, and many others. Concentration DOES NOT directly express the number of ions present in a solution. Mg. Cl 2 Mg 2+ + 2 Cl. M= moles solute liters solution 1. 0 M 2. 0 M

Sample Problems n Calculate the number of moles of Cl- ions in 1. 75 L of 1. 0 x 10 -3 M Zn. Cl 2. A chemist needs 1. 0 L of 0. 20 M K 2 Cr 2 O 7 solution. How much solid K 2 Cr 2 O 7 must be weighed out to make this solution?

n Standard Solution: a solution whose concentration is accurately known. n Example: 0. 1022 M HCl; 1. 003 M Na. OH n n n ANSWER NOW Creating dilutions Chemical analysis of a compound Theoretical Calculations What would you do to prepare a standard solution? In your answer, include specific pieces of glassware, techniques, or equipment you should use.

Dilutions n Dilution is the process used to make the solution less concentrated. moles before dilution = moles after dilution Because M =mol/L, V 1(M 1) = V 2(M 2) Lab Technique: Use a pipet to deliver the correct amount of original solution to a volumetric flask. Add some water, swirl. Fill to line, invert.

DO NOW You have a large quantity of 0. 9 M Na. OH solution available. Dilute this to 100. 0 m. L of a 0. 05 M solution. Submit your calculations and solution to your teacher.

Types of Chemical Reactions There are more than just these few types, but in this chapter we will cover… n Precipitation n Acid-base n Oxidation-Reduction

Precipitation Reactions n Precipitation Reactions (double displacement) Forms a solid precipitate from aqueous reactants. n Color of precipitate can help in identification n Solubility rules help BUNCHES n MORE…

Solubility RULES n n n All compounds containing alkali metal cations and the ammonium ion are soluble. All compounds containing NO 3 -, Cl. O 4 -, Cl. O 3 -, and C 2 H 3 O 2 - anions are soluble. All chlorides, bromides, and iodides are soluble except those containing Ag+, Pb 2+, and Hg 2+. All sulfates are soluble except those containing Hg 2+, Pb 2+, Sr 2+, Ca 2+, and Ba 2+. All hydroxides are only slightly soluble, except those containing an alkali metal, Ca 2+, Ba 2+, and Sr 2+. Na. OH and KOH are the most soluble hydroxides. All compounds containing PO 43 -, S 2 -, CO 32 -, and SO 32 - are only slightly soluble except for those containing alkali metals or the ammonium ion.

Practice Predicting n Potassium nitrate and barium chloride n Sodium sulfate and lead (II) nitrate n Potassium hydroxide and iron (III) nitrate

ALL REACTIONS SHOULD BE WRITTEN IN NET IONIC FORM

Stoichiometry of Precipitation Reactions n n Stoichiometry in a precipitation reaction is performed just like stoichiometry for a molecular reaction. You need to know which ion comes from which molecular formula.

Sample problem n Calculate the mass of solid Na. Cl needed to add to 1. 5 L of 0. 1 M silver nitrate solution to precipitate all Ag+ ions in the form of Ag. Cl. Net Ionic Eq: Ag+ + Cl- Ag. Cl

General Format n n n Write the Net Ionic Equation Calculate the moles present Identify the Limiting Reactant* Use Mole Ratio(s) Fancy-fy your answer (put in correct units)

Try Me! n What mass of precipitate will be produced when 50. 0 m. L of 0. 200 M aluminum nitrate is added to 200. 0 m. L of 0. 100 M potassium hydroxide?

Acid-Base Reactions Acids yield H+ Bases yield OH - Bases are proton acceptors n n n Acids are proton donors Definitions of acid and base vary. Arrhenius and Bronsted/Lowry are common theories. Acid-Base rxns are called NEUTRALIZATIONS

Strong Acid-Strong Base (HCl) (Na. OH) Both dissociate completely H+ + OH- H 2 O Na+ and Cl- are spectators. Weak Acid - Strong Base (HC 2 H 3 O 2) (KOH) Acetic acid will not dissociate KOH will completely HC 2 H 3 O 2 + OH- H 2 O + C 2 H 3 O 2 K+ is a spectator.

Stoichiometry sample n What volume of 0. 100 M HCl is needed to neutralize 25 m. L of 0. 35 M Na. OH? H+ + OH- H 2 O

Titrations…define me! n n n n Volumetric analysis Titration Titrant Analyte Equivalence point Indicator Endpoint

To complete a successful titration… 1. The reaction between the titrant and the analyte should be known (you should know WHAT substances you have) 2. The equivalence point should be marked accurately (you should use the right indicator) 3. Volume of the titrant needed to reach the equivalence point should be recorded accurately (you should use a buret!)

Effective Indicator Ranges

Titration Try Me Calc 1 A 50. 0 m. L sample of a sodium hydroxide solution is to be standardized. 1. 3009 M of KHP (potassium hydrogen phthalate, KHC 8 H 4 O 4) is used as the titrant. KHP has one acidic hydrogen. 41. 20 m. L of the KHP solution is used to titrate the sodium hydroxide solution to the endpoint. What is the resulting concentration of the analyte?

Titration Try Me Calc 2 n How many milliliters of a 0. 610 M sodium hydroxide solution are needed to neutralize 20. 0 m. L of a 0. 245 M sulfuric acid solution?

Norton Tutorial n n n Go to the website http: //www. wwnorton. com/college/chemistry 3/ch/17/chemtours. aspx Find the tutorial on Acid/Base ionization. Complete the tutorial question form.

Redox Reactions What is it? ? -A reaction that occurs in conjunction with a transfer of electrons. We assign oxidation states to individual atoms in a reaction to observe the change in electrons. Oxidation states are written with the +/- sign before the quantity. Ion charges are written with the +/- sign behind the quantity.

The Oxidation State of… An atom in element form A monatomic ion Fluorine in a compound Oxygen in a compound Quantity of Oxid. State Examples Zero Equal to the charge on the ion Na+, Cl- -1 , always HF, PF 3 -2, except in peroxide where it is -1 Hydrogen in a compound Na(s), O 2(g) +1, always H 2 O, CO 2, H 2 O 2 H 2 O, HCl, NH 3

n n Oxidation= an increase in the oxidation state Reduction = a decrease in the oxidation state oxidation 2 Na(s) + Cl 2(g) 2 Na. Cl(s) reduction

Metal Atom Other Atom e. Metal Ion Oxidized Substance: • Loss of electrons • Oxidation state increases • Gets Smaller • Called the Reducing Agent Other Ion Reduced Substance: The metal is oxidized and the other substance is reduced. • Gain of electrons • Oxidation state decreases • Gets Bigger • Called the Oxidizing Agent

Section 4. 10: Balancing Redox 1. 2. 3. 4. 5. 6. 7. Write the ½ reactions Balance the non-H and non-O atoms Balance O by adding H 2 O where needed Balance H by adding H+ where needed Balance charge using e. Multiply by coefficients until both e- are equal for each ½ reaction Add the ½ reactions together (cancel stuff)

Redox Sample Problem Balance: Mn. O 4 - + Fe 2+ Fe 3+ + Mn 2+ 2+ +2 8+ 1 - +7 2+ +2 0 Check Charges! 3+ +3 x 5!

Redox Try Me Problem As 2 O 3(s) + NO 3 - H 3 As. O 4 + NO(g)

1. 2. 3. 4. Repeat steps from old procedure Cancel out H+ by adding OH - ions Re-write H+ and OH- as water Add ½ reactions together (and cancel stuff)

Redox Try Me Problem 2 Balance, in base: Ag(s) + CN- + O 2 Ag(CN)2 -