Question

for each statement below, indicate whether it is true or false.

1. breaking the hydrogen bond between two water molecules is called dissociation.
2. when water dissociates, an oxygen atom separates from the rest of the molecule.
3. the hydroxide ion has an overall charge of -1.
4. a hydrogen ion is the same as a proton.
5. when a hydrogen ion separates from a water molecule, it usually combines with another water molecule to form a hydronium ion.
6. a hydronium ion has the formula h₃o⁺.
7. in pure water, at 25°c, about 10% of the water molecules are dissociated at any given time.
8. in pure water, the concentration of hydrogen ions always equals the concentration of hydroxide ions.
9. in pure water, the concentration of hydrogen ions is 1 x 10⁻⁷ molar.
10. water dissociates into oppositely charged ions.

Explanation:

1. Dissociation in water refers to breaking of the O - H bond in water molecules, not hydrogen - bond between water molecules.
2. When water dissociates, a hydrogen ion (H⁺) separates, not an oxygen atom.
3. The hydroxide ion (OH⁻) has a charge of - 1.
4. A hydrogen ion is just a proton as hydrogen atom loses its only electron to form H⁺.
5. When a hydrogen ion separates from a water molecule, it combines with another water molecule to form H₃O⁺.
6. The hydronium ion has the formula H₃O⁺, not H₂O⁺.
7. In pure water at 25°C, only about 1 in 550 million water molecules are dissociated, much less than 10%.
8. In pure water, due to the auto - ionization of water (H₂O⇌H⁺ + OH⁻), the concentration of hydrogen ions equals the concentration of hydroxide ions.
9. In pure water at 25°C, the concentration of hydrogen ions is 1×10⁻⁷ molar.
10. Water dissociates into H⁺ and OH⁻ which are oppositely charged ions.

Answer:

1. False
2. False
3. True
4. True
5. True
6. False
7. False
8. True
9. False
10. True