Density and Measurement in Science
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Questions and Answers

What is the calculated density of the irregularly shaped object?

  • 1.77 g/mL
  • 0.93 g/mL
  • 1.44 g/mL (correct)
  • 2.43 g/mL
  • To calculate the percent error for the density, what is the absolute difference used in the formula?

  • 0.33 g/mL (correct)
  • 0.33 g/mL (correct)
  • 0.01 g/mL
  • 0.44 g/mL
  • Why is a graduated cylinder preferred over a beaker for measuring liquids accurately?

  • It provides more significant figures. (correct)
  • It has a larger volume.
  • It can hold more liquid.
  • It is less fragile.
  • What is an example of an independent variable in a parachute experiment?

    <p>Size of the parachute</p> Signup and view all the answers

    Which tool is most appropriate for measuring the mass of a pencil?

    <p>Electronic balance</p> Signup and view all the answers

    What do you need to do when reading the measurement in a graduated cylinder?

    <p>Read at eye level from the bottom of the meniscus.</p> Signup and view all the answers

    What is the main purpose of an Erlenmeyer flask in a laboratory setting?

    <p>To hold liquids and facilitate swirling</p> Signup and view all the answers

    How many significant figures are in the measurement of 4.84 cm?

    <p>3</p> Signup and view all the answers

    What characterizes a physical change compared to a chemical change?

    <p>It alters only the physical properties without changing the composition.</p> Signup and view all the answers

    Which of the following is NOT an indicator of a chemical reaction?

    <p>Change in physical state</p> Signup and view all the answers

    What is the primary difference between a nuclear reaction and a chemical reaction?

    <p>Nuclear reactions involve changes in electron arrangement.</p> Signup and view all the answers

    In the context of exothermic and endothermic reactions, what happens when DHrxn is negative?

    <p>More energy is released forming bonds than was added.</p> Signup and view all the answers

    What type of bond is formed when carbon shares electrons with fluorine in CF4?

    <p>Polar covalent bond</p> Signup and view all the answers

    Which of the following processes is an example of chemical potential energy being converted to kinetic energy?

    <p>Cell respiration while running</p> Signup and view all the answers

    What occurs during the process of combustion?

    <p>Chemical energy is converted to heat and light.</p> Signup and view all the answers

    When boiling water, what type of bonds are being broken?

    <p>Intermolecular bonds</p> Signup and view all the answers

    How many moles of hydrogen gas are produced when 2 moles of methane (CH4) are combusted?

    <p>8 moles</p> Signup and view all the answers

    Which type of reaction is characterized by the splitting of a large nucleus into smaller nuclei?

    <p>Nuclear fission</p> Signup and view all the answers

    What is the molar mass of CH2F2?

    <p>52.03 g/mol</p> Signup and view all the answers

    What type of reaction involves the combination of small nuclei to form a larger nucleus?

    <p>Fusion</p> Signup and view all the answers

    During which process is light energy converted to chemical potential energy?

    <p>Photosynthesis</p> Signup and view all the answers

    Which statement accurately describes the precision of the two students' measurements of the melting point of ice?

    <p>Student A is more precise because their measurements are close together.</p> Signup and view all the answers

    Which of the following elements is classified as a noble gas?

    <p>Krypton</p> Signup and view all the answers

    What is the charge and approximate mass of a proton?

    <p>Positive charge, ~1 amu</p> Signup and view all the answers

    Which type of bond is formed between barium and sulfur?

    <p>Ionic bond</p> Signup and view all the answers

    Which of the following groups has elements that generally have 5 valence electrons?

    <p>Group 15</p> Signup and view all the answers

    Which statement is true regarding carbon isotopes?

    <p>Carbon-14 has more neutrons than both carbon-12 and carbon-13.</p> Signup and view all the answers

    What defines the order of elements in the modern periodic table?

    <p>Atomic number</p> Signup and view all the answers

    Which of the following describes a characteristic of elements in the same group?

    <p>They exhibit similar chemical properties.</p> Signup and view all the answers

    What is the proper nuclear notation for an isotope with 11 protons and 13 neutrons?

    <p>Na-24</p> Signup and view all the answers

    What is the key feature of noble gases that prevents them from forming chemical bonds?

    <p>They have a full valence shell.</p> Signup and view all the answers

    Which of the following intermolecular bonds has the weakest strength?

    <p>London dispersion forces</p> Signup and view all the answers

    What is the chemical formula for the compound formed between potassium and iodine?

    <p>KI</p> Signup and view all the answers

    How do elements in the same period compare in terms of valence electrons?

    <p>They have varying numbers of valence electrons.</p> Signup and view all the answers

    What happens to the stability of an atom when it achieves a full valence shell?

    <p>It becomes stable.</p> Signup and view all the answers

    Study Notes

    Density of an Irregularly Shaped Object

    • Mass of the object: 103 g
    • Initial water volume: 22.4 mL
    • Water level after adding object: 93.8 mL
    • Volume of the object: 93.8 mL - 22.4 mL = 71.4 mL
    • Density of the object: 103 g / 71.4 mL = 1.44 g/mL
    • Accepted density: 1.77 g/mL
    • Percent error: |1.44 g/mL - 1.77 g/mL| / 1.77 g/mL * 100% = 18.6%

    Graduated Cylinder vs. Beaker

    • Graduated cylinder provides more precision in measurements due to more graduations, resulting in more significant figures.
    • Significant figures express the uncertainty of a measurement.
    • Important practices when using a graduated cylinder:
      • Read at eye level
      • Read from the bottom of the meniscus
      • Ensure the cylinder is on a flat surface

    Scientific Experiment Terminology

    • Hypothesis: A prediction of the outcome of an experiment. (e.g., If the size of the parachute increases, then the time taken for the parachute to fall will increase, because a larger parachute will catch more air)
    • Independent Variable: The changed factor in an experiment. (e.g., Size of the parachute)
    • Dependent Variable: The measured factor in response to the independent variable. (e.g., Time taken for the parachute to fall )
    • Control: A baseline for comparison; condition where the independent variable is not changed. (e.g., No control in a parachute experiment, varying the parachute is the independent variable)
    • Constant: Items kept the same throughout the experiment, (e.g., Parachute material, shape in the parachute experiment)

    Erlenmeyer Flask

    • Shape: Sloped sides
    • Use: Holding liquids, suitable for swirling

    Ruler Measurements

    • Ruler A measurement: 4.8 cm (2 significant figures)
    • Ruler B measurement: 4.84 cm (3 significant figures)

    Measurement Units and Tools

    • Mass of a pencil: grams (g), electronic balance
    • Length of a desk: centimeters (cm), ruler or meter stick
    • Temperature of coffee: degrees Celsius (°C), thermometer or temperature probe

    Melting Point Precision and Accuracy

    • Student A is more precise (measurements close together) and accurate (close to accepted value). Student B's measurements were more dispersed.

    Scientific Notation and Standard Form

    • 0.00443 in scientific notation: 4.43 x 10-3
    • 35889 in scientific notation: 3.5889 x 104
    • 3.71 x 10-3 in standard form: 0.00371
    • 8.825 x 105 in standard form: 882500

    Atomic Structure Discoveries

    • Bohr: Electrons orbit the nucleus in specific energy levels.
    • Rutherford: Atom is mostly empty space with a dense, positive nucleus.
    • Thomson: Discovered the electron using a cathode ray experiment

    Periodic Table

    • Mendeleev: Created a periodic table arranged by atomic mass.
    • Modern Periodic Table: Organized by atomic number (number of protons)

    Periodic Table Locations of Elements

    • Metals: Left of the staircase
    • Nonmetals: Right of the staircase
    • Metalloids: Along the staircase
    • Transition Metals: Middle section (groups 3-12)
    • Halogens: Group 17
    • Alkali Metals: Group 1
    • Noble Gases: Group 18
    • Alkaline Earth Metals: Group 2

    Properties of Elements in the Same Group/Period

    • Same Group: Same number of valence electrons, similar chemical properties.
    • Same Period: Valence electrons on the same shell/principal energy level.

    Subatomic Particles

    • Proton: Positive charge, ~1 amu, located in the nucleus.
    • Neutron: No charge, ~1 amu, located in the nucleus.
    • Electron: Negative charge, ~0 amu (much smaller than proton), located in orbitals around the nucleus.

    Nuclear Notation Examples and Isotopes

    • Sodium-24: 24Na11 (11 protons, 13 neutrons, 11 electrons)
    • Sulfur-36: 36S16 (16 protons, 20 neutrons, 16 electrons)

    Carbon Isotopes and Radioactivity

    • Carbon-12, Carbon-13, and Carbon-14 are isotopes of carbon.
    • Carbon-14 is radioactive because its neutron number makes the nucleus unstable, causing it to decay for stability. Carbon-12 and Carbon-13 are stable.

    Valence Electrons by Group

    • Group 1-2: 1 to 2 valence electrons.
    • Group 13-18: 3 to 8 valence electrons.

    Atom Stability

    • Atoms become stable (lower potential energy) with a full valence electron shell (octet). This usually occurs through forming chemical bonds. Noble gases are already stable with full valence.

    Ion Formation

    • K: K+
    • Be: Be2+
    • Br: Br-
    • Al: Al3+

    Potassium and Iodine Compound

    • Formula: KI (Potassium Iodide)
    • Potassium loses electrons because it is a metal, transferring to iodine

    Barium and Sulfur Compound

    • Bond Type: Ionic bond (metal and nonmetal)
    • Formula: BaS (Barium Sulfide)

    Compound Classification

    • a. Low melting point, doesn't conduct electricity in solution: Covalent compound
    • b. Ductile, good conductor of electricity: Metal
    • c. High melting point, dissolves well in water: Ionic compound

    Intermolecular Bonding and Melting Point

    • Stronger intermolecular bonds lead to higher melting points.

    Intermolecular Bond Strength Order

    • London dispersion forces < dipole-dipole forces < hydrogen bonding < ionic bonds

    Physical vs. Chemical Change

    • Physical Change: Alters physical properties but not the composition (e.g., melting ice)
    • Chemical Change: Alters the chemical composition (e.g., rusting)
    • Indicators of Chemical Change: Color change, smell, light, temperature change, precipitate formed, gas formed

    Lewis Structures for NH3 and CF4

    • NH3: Nitrogen forms single bonds with three hydrogens. Satisfies nitrogen's need for 3 more electrons for octet configuration. Each hydrogen completes its need for one more electron.
    • CF4: Carbon forms single bonds with four fluorines. This results in each fluorine atom completing its octet, and carbon fulfilling its need of 4 electrons.

    Nuclear vs. Chemical Reactions

    • Nuclear Reaction: Changes to the atom's nucleus
    • Chemical Reaction: Changes in the arrangement of atoms to create new substances. The three nuclear types are: nuclear decay, nuclear fission (large nucleus splits), and nuclear fusion (small nuclei combine).

    Balanced Chemical Reactions and Reaction Types

    • a. C3H8 + 5O2 → 3CO2 + 4H2O (Combustion)
    • b. 2NH3 → N2 + 3H2 (Decomposition)
    • c. Al(NO3)3 + 3NaOH → Al(OH)3 + 3NaNO3 (Double Replacement)
    • d. MnO2 + 2Mg → 2MgO + Mn (Single Replacement)
    • e. 2Al + 3Cl2 → 2AlCl3 (Synthesis)

    Energy Changes in Reactions

    • Negative ΔHrxn (enthalpy of reaction): Exothermic (energy released)
    • Positive ΔHrxn: Endothermic (energy absorbed)

    Chemical Equation Calculations

    • a. Balanced equation: CH4 + 2H2O → CO2 + 4H2
    • b. ΔHrxn = 162kJ (Calculation shown in details in given text)
    • c. Endothermic (ΔHrxn is positive)
    • d. Carbon-oxygen bond in CO2: Polar covalent, Double bond( sharing 4 electrons)
    • e. Moles of H2 produced from 2 moles of CH4: 8 moles
    • f. Hydrogen-hydrogen bond in H2: nonpolar covalent single bond (Sharing 2 electrons). Electrons shared equally.

    Mole Calculations for CH2F2

    • a. Molar mass of CH2F2: 52.03 g/mol
    • b. Mass of 4.66 mol CH2F2: 242.46 g
    • c. Number of molecules in 17.6 g CH2F2: 2.04 x 1023 molecules

    Intermolecular vs. Intramolecular Bonds

    • Intermolecular: Forces between molecules
    • Intramolecular: Forces within a molecule
    • When boiling water, intermolecular bonds are being broken /disrupted.

    Endothermic/Exothermic Processes and Energy Transformations

    • Photosynthesis: Endothermic; light energy converted to chemical potential energy.
    • Cell respiration: Exothermic; chemical potential energy into heat, kinetic, and potential energy.
    • Combustion of fossil fuels: Exothermic; chemical potential energy converted to heat and kinetic energy.

    Coal and Nuclear Power Plant Comparison

    • Coal: Chemical reaction (combustion), releases CO2 and other pollutants, major source of air pollution and global warming.
    • Nuclear: Nuclear reaction (fission), produces radioactive waste, requires large amounts of water.

    Strontium-90 Half-Life

    • Half-life of Strontium-90: 25 years (Based on Graph provided).

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    Description

    This quiz covers the concepts of density calculations, precision measurement techniques using graduated cylinders versus beakers, and key scientific terminology. Test your understanding of how to accurately determine density and apply significant figures in measurements.

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