Properties of Water and Solutions

Properties of Water

• Key Properties:

  • High Melting + Boiling Point:

  • Allows water to remain liquid over a wide range of temperatures on Earth.

  • High Surface Tension:

  • Pulls water into round droplets, such as raindrops.

• Hydrogen Bonding for These Properties:

  • The hydrogen bonds that hold water molecules together are stronger than the intermolecular forces in similarly sized molecules.

  • To melt or boil water, its molecules must overcome the hydrogen bonds; hence, more energy is needed leading to higher melting/boiling temperatures.

Water Cycle Definitions

• Ground Water:

  • A layer of porous rock containing water.

• Percolation:

  • The flow of water from the surface into the soil and porous rock.

• Condensation:

  • The process of water changing from a gas to a liquid.

• Evaporation:

  • The process of water changing from a liquid to a gas.

• Transpiration:

  • The process where plants absorb water through roots and release water vapor through leaves.

• Precipitation:

  • Water condensing and falling to the ground due to gravity.

• Water Table:

  • The upper surface layer where the ground is saturated with water.

• Aquifer:

  • A body of water found beneath the Earth's surface.

• Surface Runoff:

  • Water that travels above the ground towards large bodies of water.

Mixtures and Solutions

• Heterogeneous Mixtures:

  • Molecules are not uniformly distributed.

  • Examples: Oil and vinegar, blood.

• Homogeneous Mixtures:

  • Molecules are uniformly distributed, displaying characteristics like one color and no layers.

  • Solutions:

  • A homogeneous mixture of two or more substances, made up of solute(s) and solvent(s).

• Types of Solutions:

  • Gas-Gas: Air

  • Gas-Liquid: Carbonated drinks

  • Liquid-Liquid: Alcohol in water

  • Liquid-Solid: Mercury silver amalgam

  • Solid-Liquid: Salt water

  • Solid-Solid: Alloys

• Terminologies:

  • Miscible:

  • Liquids that readily dissolve in each other.

  • Example: Ethanol in H2O

  • Immiscible:

  • Liquids that do not dissolve in each other, forming layers.

  • Example: Oil + Water

  • Dilute Solution: Low solute concentration.

  • Concentrated Solution: Very high solute concentration.

  • Electrolytic Solution: Aqueous solutions of ionic solutes called electrolytes.

  • Nonelectrolytes: Solutions of molecular compounds.

  • Strong Electrolyte: Fully dissolves in water.

  • Weak Electrolyte: Partially dissolves in water.

  • Hydrated Ions: Ions surrounded by water molecules when electrolytes dissolve.

The Dissolving Process

• Three Steps:

  1. Solute molecules must separate: Ionic bonding/intermolecular forces break between the solute ions/molecules (Endothermic process - requires energy).

  2. Some solvent molecules separate (Endothermic process - requires energy).

  3. New intermolecular forces form between solute and solvent molecules (Exothermic process - releases energy).

• Dissociation Equations:

  • Example: Potassium Chloride Dissociation.
    KCl(aq) \rightarrow K^+(aq) + Cl^-(aq)

• Like Dissolves Like:

  • Ionic/polar compounds dissolve well in polar solvents but not in non-polar solvents.

  • Non-polar substances dissolve well in non-polar solvents but not in polar solvents.

• Solubility Curve:

  • On the line = saturated solution

  • Under the line = unsaturated solution

  • Above the line = supersaturated solution

• Solubility and Saturation:

  • Saturated Solution: Maximum solute amount dissolved in a solvent.

  • Unsaturated Solution: Less than maximum solute amount.

  • Supersaturated Solution: More than maximum solute amount.

  • Positive Slope Curve: Ionic compounds; solubility increases with temperature.

  • Negative Slope Curve: Gases; solubility decreases with temperature.

Concentration and Dilution

• Concentration Formula:
  c = \frac{n}{V}

  • Where n is the number of moles and V is the volume.

  • Defines the quantity of solute in a solvent.

• Dilution Process:

  • Lowering the concentration of a solution by adding solvent.

  • The number of moles of solute remains constant.

• Formulas for Dilution:

  • n = C_{c} V_{c}

  • n= C_{d} V_{d}

  • C_c = Concentration of concentrated solution.

  • V_c = Volume of concentrated solution.

  • C_d = Concentration of diluted solution.

  • V_d = Volume of diluted solution.

  • Relate concentrations of solutions:

  • C_{c} V_{c} = C_{d} V_{d}

• Percentage Calculations:

  • Percentage W/W:
    C{w/w} = \left( \frac{m{solute}}{m_{solution}} \right) \times 100\%

  • Percentage W/V:
    C{w/v} = \left( \frac{m{solute}}{v_{solution}} \right) \times 100\%

  • Percentage V/V:
    C{v/v} = \left( \frac{v{solute}}{v_{solution}} \right) \times 100\%

• PPM, PPB, PPT Calculations:

  • PPM:
    \left( \frac{m{solute}}{m{solution}} \right) \times 10^6

  • PPB:
    \left( \frac{m{solute}}{m{solution}} \right) \times 10^9

  • PPT:
    \left( \frac{m{solute}}{m{solution}} \right) \times 10^{12}