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General Biology: Moles, Molecules, and pH Practice Problems

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  • How do we obtain a mole of sucrose (C12H22O11)?
    A mole of sucrose is obtained by measuring out its molar mass in grams, which is the sum of the atomic masses of all atoms in the formula.
  • How many molecules does one mole of sucrose contain?
    One mole of sucrose contains 6.022 × 1023 molecules, Avogadro's number.
  • How do we obtain a mole of glucose (C6H12O6)?
    A mole of glucose is obtained by weighing its molar mass in grams, calculated by summing the atomic masses of all atoms in glucose.
  • How many molecules does one mole of glucose contain?
    One mole of glucose contains 6.022 × 1023 molecules, Avogadro's number.
  • How many molecules does a mole of ethanol (C2H6O) contain?
    A mole of ethanol contains 6.022 × 1023 molecules, Avogadro's number.
  • How many atoms are in a mole of sucrose (C12H22O11)?
    A mole of sucrose contains \(12+22+11=45\) atoms per molecule, so total atoms = \(45 \times 6.022 \times 10^{23}\) atoms.
  • How many grams of sucrose are needed to make 1 L of 0.5 M sucrose solution?
    Mass = Molarity × Volume × Molar mass; for 0.5 M and 1 L, mass = 0.5 × 1 × 342 g/mol = 171 g sucrose.
  • What is the H+ concentration [H+] if the pH of a solution is 8?
    [H+] = \(10^{-8}\) M.
  • What is the OH- concentration [OH-] if the pH of a solution is 8?
    [OH-] = \(10^{-14} / 10^{-8} = 10^{-6}\) M, using \(K_w = 10^{-14}\).
  • What is the H+ concentration [H+] if the pH of a solution is 3?
    [H+] = \(10^{-3}\) M.
  • What is the OH- concentration [OH-] if the pH of a solution is 3?
    [OH-] = \(10^{-14} / 10^{-3} = 10^{-11}\) M.
  • If the pH of an aqueous solution is 4, is it acidic, neutral, or basic?
    A solution with pH 4 is acidic because pH < 7.
  • A solution of pH 3 has a [H+] that is how many times greater than a solution of pH 6?
    [H+] difference = \(10^{6-3} = 10^{3}\); the pH 3 solution has 1000 times more H+.