Chemistry 1st Assessment PDF

Chemistry 1st assessment 1. The classification of chemical analysis methods. According to the reaction’s type, volumetric analysis is divided into 4 classes - Neutralization: Components are either acids or bases and can be titrated with a standard solution of a strong base or strong acid....

Chemistry 1st assessment 1. The classification of chemical analysis methods. According to the reaction’s type, volumetric analysis is divided into 4 classes - Neutralization: Components are either acids or bases and can be titrated with a standard solution of a strong base or strong acid. The reactions involve the combination of hydrogen and hydroxide ions to form water. - Precipitation: This method uses chromate (CrO42- ) as an indicator. Chromate forms a precipitate with Ag+. The first drop of Ag+ in excess will react with the chromate indicator giving a reddish color. - Complexometry: In this method the titrant is a complexing agent and forms a water-soluble complex with the analyte, a metal ion. - Redoxometry: In “redox” titrations involves the titration of an oxidizing agent loses electrons and a reducing gains electrons in a reaction bw them. LEO “says” GER Lose Electrons= Oxidation 0 +1 Na → Na + e- Sodium is oxidized Gain Electrons= Reduction 0 -1 Cl + e → Cl Chlorine is reduced - 2. Units of mass and quantity of material. Mass: (g) grams Volume: (L) liter, (mL) milliliters 3. Definition of chemical equivalent. When the solution is dropped into another known solution´s volume till the equivalence point is reached. In titration is a practical and experimentally determinable point. The equivalence point is the moment when the reactants have reacted completely, with no excess or deficit of either the analyte or the titrant. The color change would happen when you mix the 2 solutions together in exactly equation proportions. 4. Calculation of element, compound, oxidizer and reducer equivalents. Oxidizer (oxidants): are the ones that take electrons which will make them oxidizers. Reducers (reductants): Are the ones that give electrons which will make them reducers 5. The basic laws of stoichiometry. The total mass if the reactants equals the total mass of the products 6. Titrimetric methods of analysis, classification. - Classification of volumetric (titrimetric) methods - Expressions of concentration - Mathematical expression of equivalent point - Accuracy and precision - Apparatus and glassware for titrimetric analysis - Volumetric analysis solutions - Neutralization titration - Indicators 7. Volumetric analysis solutions. Define standard and titrated solutions. How to prepare them? Standard solution: A reagent of known concentration, stable and reactive, used in titrimetric analysis. It’s prepared by dissolving an accurate weight of a pure reagent in water and diluting to a known volume. The concentration of standard solution is prepared by dissolving an accurate weight of pure reagent in water that is then dilute to an exactly known volume. Titrated (work/process) Solution: Solutions with approximate concentration, prepared from unstable or reactive materials, whose exact concentration is determined by titration with a standard solution. 8. Method of neutralization titration. Equivalence point, mathematical expression of equivalence point. Neutralization titration: This method involves a reaction bw an acid and a base resulting in a neutral solution at pH 7 (for strong acid- strong base reactions) Equivalence point: The point at which reactants have completely reacted with no excess. Mathematically, at the equivalence point: Cn1 * V1 = Cn2 * V2 where Cn represents normality and V represents volume. 9. Estimation and calculation of concentration of titrated solutions. Concentration (normality, Cn) can be calculated by the equation Cn= m / E*V where m is the solute mass, E is the equivalent weight, and V is the solution volume. Neutralization titration: reaction bw an acid and a base which produces a neutral solution (pH=7) acid+ + base– → salt + water In an acid- base titration, the experimenter will add a base of known concentration to an acid unknown concentration ( or the other way around) Neutralization method: is a method of volumetric analysis based on the neutralization reaction of H+ and OH– ions. H3O+ + OH– = 2H2O, H+ + OH– =H2O In titration process concentration of H+ ions and pH values change. In dependence of strength of reacting acids and alkine, pH in equivalent point can be pH=7, pH7 Types of neutralization reaction: 1) Strong acid + Strong base → Salt + Water HCl + NaOH → NaCl + H2O 2) Strong acid + Weak Base → Salt + Water HCl + NH4OH → NH4Cl + H2O 3) Weak acid + Strong Base → Salt + Water CH3COOH + NaOH → CH3COONa + H2O 4) Weak acid + Weak Base = Salt + Water CH3COOH + NH4OH = CH3COONH4 + H2O 10. Explain the titration curves, specify the indicators, when: Strong acid is titrated with strong alkali; HCl + NaOH → NaCl + H2O - Equivalent point pH=7 - Hydrolysis of salt does NOT occur - Indicator Methyl Orange - HCl and NaOH are typical strong acid and strong base When running base into the acid: When the acid and the base have been added in exactly equivalent points, the solution contains only NaCl and H2O. The pH value of the solution is 7.00 In the beginning of titration the solution of strong acid is red. During titration and decrease of acid amount solution becomes orange. Titration proceeds until the solution turns yellow after one NaOH drop. Strong alkali is titrated with strong acid; 2 NaOH + 2 HCl = 2 NaCl + 2 H2O - Equivalent point pH=7 - Hydrolysis of salt does NOT occur - Indicator Methyl Orange In the beginning of titration the solution of the strong base is yellow. Titrate with HCl will make it orange  Weak acid is titrated with strong alkali. CH3COOH + NaOH → CH3COONa + H2O - Equivalent point pH=7 - The Salt is hydrolysed CH3COONa ↔ CH3COO– + Na+ CH3COO – + HOH ↔ CH3COOH + OH– [OH–]>[H+] Most of the time we use the common indicator Phenolphthalein Phenolphthalein is clear in acid Light pink in neutral Dark pink in base 11. Expressions of concentration in volumetric analysis: molarity, normality, percent concentration, titer. Expression of concentration: Concentration is a property of a mixture calculated by dividing one amount by another. Molarity M is the number of gram moles of reagent contained in one liter solution (mol/L). - C M = nA / V Molarity M = Number of mole / volume of solution (L) Normality N Is the Number of gram equivalents contained in one liter of solution. Cn= Number of equivalent / Volume (L) - Cn= m / E*V - m- solute’s mass (g) - E- solute’s equivalent - V- solution’s volume (L) Percent concentration C%: Describes how much grams of material is dissolved in 100 grams if solution - C% = msubstance / msolution *100% - If mass is used the concentration is called weight by weight (W/W) - If volume is used for the solvent then the ration is weight by volume (W/V) Titer is the number of solute’s grammes in the one cm3 (ml) of the solution (g/cm3 ). A transition bw molar concentration of equivalent and titer: - T= CN * E / 1000 g/ml (g/cm3 ) 12. Calculation of molar concentration and titer of solution according to data of titration. Molar concentration and titer can be derived using titration data, applying the law of equivalent proportions. At the equivalence point, the product of the titrant’s concentration and volume equals the product of the analyte’s concentration and volume, allowing for calculations based on this relationship. 13. Complex compounds, nomenclature. Coordinative bond, coordination number. Nomenclature: The formula of complex ions is out in square brackets, and it is placed at the front if its charge is positive. The name of complex captions starts with the greek from the coordinator number (mono-, di-, tri-, and etc) and then comes the name of the ligand, plus the name of the metal ion with valence state indicated. Coordinative bond: A covalent bond where two atoms share electrons with each other. Coordination number: The total number of atoms, ions, or molecules bonded to the atom. 14. Werner’s coordination theory points. The structure of complex compounds according to Werner's coordination theory. Explains that metals in coordination compounds exhibit primary valency( oxidation state) and secondary valency (coordination number). These secondary valencies are spatially directed, leading to specific geometries. For example, potassium ferrocyanide has Fe as the central ion with a coordination number of 6. 15. Method of complexometry. Complexone. Application of EDTA and Trilon B in complexometry. Complexone: Any chelating agent used for the analytical determination of metals. With numerous ions of metals they form stable complex compounds, called complexonates. Chelating agent: can be defined as organic compounds which complex or sequester metal ions. EDTA: Complexonates is mostly used for analysis EDTA (ethylene- diammine tetraacetic acid) Trilon B: Salt of it (disodium ethylenediaminetetraacetate) 16. Water hardness. Classification. Which salts maintain temporary and permanent water hardness? Write down the formulas of these salts. Water hardness can be either temporary or permanent. Temporary: Carbonate hardness. Is caused by Ca(HCo3)2 and Mg(HCo3)2 dissolved in water. Permanent: Non- carbonate hardness. Is mainly caused by Ca2+/ Mg2+ sulfates. chlorides, silicates, phosphates and nitrates. Salts that maintains: Calcium and magnesium Formulas: Mg2+ + In— = [Mg In]+ 17. Methods and reactions of water softening. Water softening: A process in which the ions of calcium, magnesium and sometimes iron are removed. Ca(HCO3)2 →CaCO3 ↓+ CO2 ↑ + H2O Mg (HCO3)2 → MgCO3 ↓+ CO2 ↑+ H2O 18. How is the temporary, permanent and total water hardness determined and calculated? Temporary hardness: Can be removed by boiling. Caused by dissolved bicarbonate minerals like calcium and magnesium. Temporary Hardness=[HCO3−​]×conversion factor (to CaCO3​) Permanent hardness: Caused by other dissolved minerals, like calcium sulfate and magnesium sulfate, which can not be removed by boiling and will remain in the water. Permanent Hardness=Total Hardness−Temporary Hardness Total hardness: The sum of temporary and permanent hardness, representing the total concentration of calcium and magnesium ions in the water. Total Hardness (mg/L CaCO3​)= (Volume of EDTA × Molarity of EDTA × Equivalent Weight of CaCO3​​) / Sample Volume Temporary Hardness is found by boiling and titration. Permanent Hardness is derived by subtracting temporary hardness from total hardness. Total Hardness is measured directly via EDTA titration. 19. Oxidation reduction processes. Oxidation numbers (states), calculation of them. Oxidation reduction (redox) reactions: Involve changes in oxidation numbers, where oxidation is the loss of electrons (increase in oxidation number) and reduction is the gain of electrons (decrease in oxidation number). +III Al → Al3+ + 3e– Al3+ is now oxidized, it got the oxidation number +III -I Cl2 + 2e → 2Cl– – Cl– is now reduced. it gets the oxidation number -I 0 Al(s) = Al 0 Cl2 (g)= Cl2 -III+I -III +I +I +I -3 + +3 N H3 ↔ N H H H (it has to be= to 0) (-III + (+III))= 0 +V-II +V +V -II -II -II -II -II N2 O5 ↔ N N O O O O O =0 +VI -II +VI -II -II -II -II –2 S O42- ↔ S O O O O =-2 20. Redox equations. Formation and balancing of equations for these reactions. Redox reactions are when we combine both an oxidation and a reduction into a single reaction. Example: Oxidation: 2Na → 2Na+ + e– Reduction: Cl2 + 2e– → 2Cl– Product: 2NaCl 21. Methods of redoximetry, classification of them. Redoximetry methods are classified based on whether they use oxidizing or reducing agents in titration. This includes titrations where substances like potassium permanganate or iodine are used as standard oxidants or reductants. 22. Qualitative analysis: Irreversible reactions. Irreversible reactions in qualitative analysis are those that proceed to completion, often driven by the formation of products that are insoluble, gaseous, weak electrolytes or complex compounds. Analytical reactions in electrolyte solutions. Analytical reactions in electrolyte solutions often produce distinct observable changes known as analytical signals that include the presence of certain ions. Reactions of flame coloration. Flame tests are a quick method to detect the presence of certain metal ions based on the color they impart to a flame when heated. Each metal ion produces a characteristic color due to the excitation of electrons, which release energy as visible light when they return to their ground state. Examples of typical flames: Sodium (Na⁺): Bright yellow (intense and persistent) Potassium (K⁺): Pale violet (faint and fleeting) Calcium (Ca²⁺): Brick red or orange-red Strontium (Sr²⁺): Crimson red Barium (Ba²⁺): Light green Copper (Cu²⁺): Green or blue 23. Solutions, classification of solutions. Solutions are classified based on particles size and state: True solutions: have particles 500 nm and are heterogenous 24. True solutions: Solubility. Factors related to solubility.  Factors affecting the “rate” of solubility. Concentration of solutions: Mass percent solution; Molarity; Molality, Mole fraction. Calculations. 25. Physical properties of true solutions: vapour pressure and Raoult’s law; melting point; boiling point; osmotic pressure. Vapor pressure: In a solution, the presence of a non- volatile solute reduces the solvent vapor pressure compared to its pure state. This is because solute molecules occupy surface area, decreasing the number of solvent molecules available to escape into the vapor phase. Raoult’s Law: For ideal solutions, this law states that the vapor pressure of the solution (Psolution) is directly proportional to the mole fraction of the solvent (X solvent) in the solution