Basics of Chemistry: Mole Concept
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Questions and Answers

What type of molecule is O2?

  • Heteroatomic
  • Homoatomic (correct)
  • Inorganic
  • Polyatomic

    • Which of the following compounds is heteroatomic?

  • P4
  • Cl2
  • O3
  • NaOH (correct)

    • What is the molecular weight of H2SO4?

  • 63
  • 40
  • 98 (correct)
  • 74

    • How many moles are in 180g of water (H2O)?

    <p>2</p> Signup and view all the answers

    How many protons are in 1 mole of H2SO4?

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

    What type of molecule is glucose (C6H12O6)?

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

    Who discovered the electron?

    <p>J.J Thomson</p> Signup and view all the answers

    Which particle is not considered part of the atom's nucleus?

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

    What is the product of the chemical reaction HCl + NaOH?

    <p>NaCl + H2O</p> Signup and view all the answers

    Which combination represents an alpha particle?

    <p>2p + 2n</p> Signup and view all the answers

    What type of reaction is represented by the equation 90233Th + 24He -> 92237U?

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

    What is defined as one atomic mass unit (amu)?

    <p>1/12 the mass of a C-12 atom</p> Signup and view all the answers

    Which of the following accurately describes isotopes?

    <p>Isotopes have same atomic number but different atomic masses</p> Signup and view all the answers

    Which element is chosen as the standard for atomic mass?

    <p>Carbon-12</p> Signup and view all the answers

    What is the average atomic mass calculated based on?

    <p>Sum of atomic weights multiplied by percent abundance</p> Signup and view all the answers

    What would be the mass of 100 Si-28 atoms in amu?

    <p>5600 amu</p> Signup and view all the answers

    What is the particle size range of a colloid?

    <p>1 - 100 nm</p> Signup and view all the answers

    Which of the following is an example of a heterogeneous mixture?

    <p>Sand + water</p> Signup and view all the answers

    What constitutes matter?

    <p>Anything that has mass and occupies space</p> Signup and view all the answers

    What defines a mixture?

    <p>A physically distinct and mechanically separable entity</p> Signup and view all the answers

    Which of the following is true about a suspension?

    <p>Particles are larger than 100 nm</p> Signup and view all the answers

    What is a limiting reagent in a chemical reaction?

    <p>The reactant that gets completely consumed</p> Signup and view all the answers

    Which of the following accurately describes the reaction ratio given in the example N2 + 3H2 -> 2NH3?

    <p>1:3:2</p> Signup and view all the answers

    In the equation 3A + 6B -> 3C + 5D, if 9 mol A and 27 mol B are used, what is the limiting reagent?

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

    What method is mentioned for determining the limiting reagent?

    <p>Method of Assumption</p> Signup and view all the answers

    If 20 mol of N2 require how many moles of H2 to fully react according to the stoichiometric ratio in the example N2 + 3H2 -> 2NH3?

    <p>60 mol H2</p> Signup and view all the answers

    What does a chemical reaction primarily involve?

    <p>Rearrangement of atoms from reactant molecules</p> Signup and view all the answers

    Which statement accurately describes stoichiometry?

    <p>It studies chemical reactions and their calculations</p> Signup and view all the answers

    What is conserved during a chemical reaction?

    <p>Atoms and their masses</p> Signup and view all the answers

    Why is the equation $SO_2 + rac{1}{2} O_2 ightarrow SO_3$ considered fundamentally incorrect?

    <p>It contains non-integer coefficients</p> Signup and view all the answers

    What does the 'g' represent in stoichiometric equations?

    <p>Number of molecules or moles</p> Signup and view all the answers

    What is the empirical formula for glucose?

    <p>C1H2O</p> Signup and view all the answers

    What is the percentage by mass of hydrogen in the given calculation?

    <p>6.67%</p> Signup and view all the answers

    Which of the following compounds is known as blue vitriol?

    <p>CuSO4.5H2O</p> Signup and view all the answers

    What does the term 'multiplication factor' refer to in the context of empirical and molecular formulas?

    <p>The ratio of the molecular formula to the empirical formula</p> Signup and view all the answers

    What is the molecular formula for glucose?

    <p>C6H12O6</p> Signup and view all the answers

    What is the final amount of B in the reaction 7A + 6B → 3C + 4D?

    <p>6</p> Signup and view all the answers

    In the reaction 2A + 3B → 1C + 4D, what is the amount of C formed?

    <p>24.9</p> Signup and view all the answers

    Which substance is the limiting reactant in the reaction 2A + 3B → 1C + 4D?

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

    How many moles of D are produced when using the limiting reactant in the reaction 7A + 6B → 3C + 4D?

    <p>12</p> Signup and view all the answers

    What is the molar ratio used to determine the limiting reactant in a chemical reaction?

    <p>Number of moles / Reaction coefficient</p> Signup and view all the answers

    What is the final amount of A in the reaction 2A + 3B → 1C + 4D after the reaction?

    <p>3.34</p> Signup and view all the answers

    What formula represents percentage purity?

    <p>Actual quantity = % purity x theoretical yield / 100</p> Signup and view all the answers

    Which of the following factors can lead to a lower percentage yield?

    <p>Some reactants might escape</p> Signup and view all the answers

    How is percentage yield calculated?

    <p>Actual yield / theoretical yield x 100</p> Signup and view all the answers

    Which formula accurately expresses the percentage composition of an element in a compound?

    <p>% of element = mass of element / mol wt x 100</p> Signup and view all the answers

    What does the establishment of equilibrium in a reaction imply?

    <p>No further reaction occurs as forward and reverse rates equalize</p> Signup and view all the answers

    What should you do if the total percentage composition does not equal 100?

    <p>Subtract the total from 100 to find the percentage of oxygen.</p> Signup and view all the answers

    How is the empirical formula determined from the number of moles of elements?

    <p>By dividing the number of moles by the smallest number of moles.</p> Signup and view all the answers

    Which step is necessary to obtain the molecular formula from the empirical formula?

    <p>Calculate the ratio of the molecular weight to the empirical weight.</p> Signup and view all the answers

    What does the Law of Conservation of Mass state?

    <p>The total mass of reactants equals the total mass of products.</p> Signup and view all the answers

    What does the Law of Definite Proportion indicate?

    <p>The ratio in which elements combine to form a compound is always fixed.</p> Signup and view all the answers

    Study Notes

    Mole Concept & Equivalent Concept

    • Matter is any substance that has mass and occupies space, categorized as either pure or a mixture.
    • Pure substances can be elements (e.g., O2, Na) or compounds (e.g., H2O, NaCl), while mixtures can be homogeneous or heterogeneous.
    • Homogeneous mixtures have uniform composition, whereas heterogeneous mixtures contain distinct phases.

    Colloid & Suspension

    • Colloids consist of particles sized between 1 - 100 nm and exhibit the Tyndall effect, examples include sand-water and oil-water mixtures.
    • Suspensions contain larger particles greater than 100 nm, such as S8 crown sulfur.

    Atomic Structure

    • Atom: smallest indivisible unit participating in chemical reactions.
    • Key scientists and their discoveries include:
      • J.J. Thomson - Electron
      • Goldstein - Proton
      • Chadwick - Neutron
      • Rutherford - Nucleus

    Chemical Reactions

    • Chemical reactions involve rearrangement of atoms, maintaining mass conservation (total mass of reactants = total mass of products).
    • Types include chemical and nuclear reactions (e.g., HCl + NaOH vs. 90233Th + 24He).

    Atomic Mass

    • Atomic mass unit (amu) is defined as 1/12 of the mass of a C-12 atom.
    • Isotopes share the same atomic number but differ in mass; C-12 is the standard due to stability.

    Molecules

    • Molecules are formed from atomic groups, classified as homoatomic (e.g., O2, Cl2) or heteroatomic (e.g., H2O, CO2).
    • A molecule of O2 consists of 2 atoms; 1 mole of glucose contains 6 C, 12 H, and 6 O atoms.

    Molecular Weight

    • Molecular weights vary among compounds, given for a variety of substances (e.g., H2O = 18, H2SO4 = 98).
    • Calculation of moles can be done with the formula: number of atoms = given mass/atomic weight.

    Stoichiometry

    • Stoichiometry is involved in the quantitative relationships of reactants and products in chemical reactions.
    • Example reaction: 2SO2 + O2 → 2SO3, with the stoichiometric ratios of 2:1:2.

    Limiting Reagent

    • A limiting reagent is a reactant that is consumed first, halting the reaction; the excess reagent remains unreacted.
    • Calculating limiting and excess reagents involves understanding initial amounts and stoichiometric relationships.

    Chemistry Calculations

    • Ratios must be used in calculations of limiting reactants to determine product formation accurately.
    • Percentage yield and percentage purity calculations help assess the efficiency of reactions.

    Empirical & Molecular Formulae

    • Empirical formulas represent the simplest whole number ratio of elements, while molecular formulas indicate the exact number of atoms.
    • Steps for determining empirical formula from % composition include calculating moles, establishing the ratio, and deriving both empirical and molecular formulas.

    Laws of Chemical Combination

    • Law of Conservation of Mass: Mass is neither created nor destroyed; total mass of reactants equals total mass of products.
    • Law of Definite Proportion: Elements combine in fixed ratios to form compounds, regardless of the source.

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    Description

    Explore the fundamental concepts of matter and mixtures in chemistry, focusing on the mole concept and equivalent concepts. Understand the distinction between pure substances, elements, and compounds, as well as homogeneous and heterogeneous mixtures.

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