Volumetric analysis

Chemical equation a A + b B + .... x X + y Y + ... = reactants products a , b … stoichiometric coefficients (numbers) nA a nB b = Stoichiometry - describes the ratio of molecules in chemical reactions

Calculations from chemical equations H2SO4 + 2 NaOH Na2SO4 + 2 H2O reactants products nsulfuric acid 1 nsodium hydroxide 2 = How much of NaOH is necessary for a full neutralization of 1.5 mol of H2SO4 ? ? mol 5.0 g The answer: 3 mol ? g 150 mL of 40% sol. ? mL of ... 200 mL of 0.1 M sol.

Balancing chemical equations Reaction: silver nitrate + potassium chromate nomenclature ! AgNO3 K2CrO4 2 Ag2CrO4 + KNO3 AgNO3 + K2CrO4 2 1) identify the products 2) add stoichiometric numbers - to balance the number of atoms 3) check whether it is correct

2 Ag+ + CrO42- Ag2CrO4 Ionic equations AgNO3 Ag+ + NO3- aqueous solutions: electrolytes disociate AgNO3 Ag+ + NO3- K2CrO4 2 K+ + CrO42- Use only the ions that participate in the reaction! 2 Ag+ + CrO42- Ag2CrO4 reddish brown precipitate

In redox reactions, all is about electrons. difficult to balance ! And you must be able to do so ! In redox reactions, all is about electrons. OXIDATION = loss of electrons (increase in oxidation state) REDUCTION = gain of electrons (decrease in oxidation state) OXIDATION and REDUCTION are coupled processes! If something gets oxidized, something else must get reduced.

Balancing redox equations Reaction: Fe2+ + MnO4- KMnO4 potassium permanganate - strong oxidizing agent oxidizing agent = it has the ability to oxidize the others  it must get reduced itself MnO4- + 8 H+ + 5 e- Mn2+ + 4 H2O MnO4- oxidation state of the Mn atom is VII Mn2+ oxidation state of the Mn atom is II The change in oxidation state is by 5 (electrons).

Balancing redox equations MnO4- + 8 H+ + 5 e- Mn2+ + 4 H2O This "half reaction" is a reduction. Fe2+ Fe3+ + e- This "half reaction" is an oxidation. Let's put both together... 1 x MnO4- + 8 H+ + 5 e- Mn2+ + 4 H2O 5 x Fe2+ Fe3+ + e- MnO4- + 5 Fe2+ + 8 H+ Mn2+ + 5 Fe3+ + 4 H2O

Volumetric analysis a A + b B + .... x X + y Y + ... = a The principle is a reaction of: a sample + a standard solution (with known concentration) nA a nB b = n = c x V a b cA x VA = x cB x VB

Titration a b cA x VA = x cB x VB

Laboratory equipment for titrations 1) pipettes 2) burette 3) flasks

Automatic pipettes

Indicator is a substance which makes the end point (equivalence point) of the titration apparent by a change in colour

Standardization = estimation of the accurate concentration of a standard solution by means of its titration with a primary standard solution (a very stable solution with known concentration)

Titrations methods according to the type of reaction displacement of ions a) Neutralization reactions (alkalimetry, acidimetry) H+ + OH- H2O b) Formation of precipitate (argentometry) Me+ + X- MeX (non-soluble precipitate) c) Formation of complexes (chelatometry, mercurimetry) Me+ + X- [MeX] (soluble complex) electron transfer a) Oxidimetry (manganometry, iodometry) b) Reductimetry (thiosulphatometry)

What to know about? Standard reagent Standardization (primary standards) Indication of the equivalence point (titration endpoint) What kind of samples can be analyzed?

Acid base indicators

Titration curves

Titration curves

Titration curves

Chelatometry standard reagent: EDTA ethylenediaminetetraacetic acid

Chelatometry