Sem 1 Chemistry Final Exam Review 24-25

Unit 1 - Chemistry Fundamentals

  • Differences between Metals and Nonmetals:

    • Metals: typically have high melting points, are good conductors of electricity, and tend to lose electrons (form cations).

    • Nonmetals: usually have lower melting points, are poor conductors and tend to gain electrons (form anions).

  • Meniscus Reading Importance:

    • Accurate volume measurements are made by reading the bottom of the meniscus, which helps avoid parallax errors and ensures precision in lab measurements.

  • Volume Measurement:

    • Example reading: 20.7 mL considering significant figures.

  • Conversions:

    • 108.6 kg to grams:

      • 108.6 kg x 1000 g/kg = 108600 g

  • Density Calculation:

    • Rock mass: 19.3 g

    • Initial water volume: 27.4 mL

    • Final water volume: 36.5 mL

    • Displaced volume = Final - Initial = 36.5 mL - 27.4 mL = 9.1 mL

    • Density = Mass/Volume = 19.3 g / 9.1 mL = 2.12 g/mL

  • Precision vs. Accuracy:

    • Precision: Students' measurements (52.3 g, 52.3 g, 52.3 g) are consistent.

    • Accuracy: Actual mass is 50.0 g, indicating the measurements are precise but not accurate.

  • Scientific Notation Conversion:

    • Convert 7.89×10−5 to decimal: 0.0000789.

  • Physical vs. Chemical Changes:

    • Physical Change: Composition remains unchanged (e.g., melting ice, dissolving sugar).

    • Chemical Change: Composition changes, creating new substances (e.g., rusting metal, burning wood).

  • Signs of Chemical Change:

    • Change in color, gas production (bubbles), and change in odor are indicators of a chemical change.

Unit 2 - Atomic Structure & Periodic Table

  • Atom Structure:

    • Protons and neutrons located in the nucleus; electrons orbit around the nucleus.

  • Element Properties:

    • Halogen in 5th period: Iodine.

    • Alkaline earth metal in 2nd period: Beryllium.

    • Noble gas in period 1: Helium.

    • Element with 26 protons: Iron.

  • Atomic Number vs. Mass Number:

    • Atomic number: Number of protons in nucleus.

    • Mass number: Total number of protons and neutrons. Example: Sodium-11 (11 mass), Sodium-13 (13 mass).

  • Difference between Ions and Isotopes:

    • Ion: Atom or molecule with a net electric charge due to losing or gaining electrons.

    • Isotope: Variant of an element with the same number of protons but different number of neutrons.

  • Average Atomic Mass Calculation:

    • Isotopes and their abundances: 34X (52.04%), 36X (22.96%), 37X (2.28%), 38X (22.72%).

    • Average atomic mass formula: (34 * 0.5204) + (36 * 0.2296) + (37 * 0.0228) + (38 * 0.2272).

  • Electron Configurations:

    • Krypton: [Kr] 5s² 4d¹⁰ 5p⁶.

    • Magnesium: [Ne] 3s².

Unit 3 - Chemical Bonding

  • Octet Rule in Bonding:

    • Atoms tend to gain, lose, or share electrons to have 8 electrons in their outer shell, leading to chemical bonding.

  • Bond Types and Compounds:

    • Bond between magnesium and oxygen forms an ionic bond (MgO).

  • Reactivity and Valence Electrons:

    • Valence electrons dictate reactivity; compare sodium (1), boron (3), and iodine (7).

    • Sodium: readily loses one electron, boron: shares three, iodine: gains one electron.

  • Ionic vs. Covalent Bonds:

    • Ionic Bonds: transfer of electrons; example: NaCl.

    • Covalent Bonds: sharing of electrons; example: H₂O.

  • Ions Formation:

    • Metals tend to lose electrons and form cations; nonmetals gain electrons and form anions.

  • Lewis Dot Diagrams:

    • Draw diagrams for iodine, phosphorus, and francium.

  • Nomenclature:

    • Cu(NO₃)₂ is named copper(II) nitrate; Roman numeral indicates the charge of the copper ion because it is a transition metal.

Unit 4 - The Mole

  • Definition of Mole:

    • A mole is a unit in chemistry that measures quantity, equivalent to 6.02 × 10²³ particles such as atoms, molecules, ions, etc.

  • Molar Mass Calculation:

    • Molar mass of calcium phosphate, Mg₃(PO₄)₂, by summing the atomic masses of constituent elements:

      • Mg = 24.31 g/mol, P = 30.97 g/mol, O = 16.00 g/mol.

  • Weight of Moles:

    • 1 mole of carbon weighs approximately 12.01 g, bromine gas (Br₂) weighs approximately 159.81 g, Al₂(SO₄)₃ weighs approximately 342.86 g.

  • Moles Calculation:

    • For HCl: 28.5 g / 36.46 g/mol = 0.782 moles.

    • For H₂O: 5 g / 18.02 g/mol = 0.277 moles.

  • Percent Composition:

    • Percent composition of Mg₃(PO₄)₂ involves dividing the mass of each component by total molar mass and multiplying by 100.

Unit 5 - Chemical Reactions

  • Conservation of Mass:

    • In a balanced chemical reaction, the total mass of products equals the total mass of reactants, demonstrating the conservation of mass.

  • Chemical Reactions with Aluminum:

    • Full chemical equation when aluminum reacts with H₂SO₄ to produce hydrogen gas and aluminum sulfate:

    • 2 Al (s) + 3 H₂SO₄ (aq) → 3 H₂ (g) + Al₂(SO₄)₃ (aq).

  • Reaction Types:

    • Identify potassium and bromine reaction as synthesis: K + Br₂ → 2 KBr.

    • CaCl₂ + Na₃PO₄ → Ca₃(PO₄)₂ + 3 NaCl is a double replacement reaction.

  • Activity Series:

    • Using the activity series: Identify non-reactive cases (Cu + HCl).