ID

Chemistry and Water

Matter

  • Matter - anything that takes up space, has mass.

  • Element - substance cannot be broken down by chemical reaction (i.e. copper)

  • Compound - consists of 2+ elements combined in fixed ratio.

  • 92 natural elements, 25% essential.

  • Carbon, oxygen, nitrogen, hydrogen, phosphorus, sulfur are included.

Isotopes:

  • Isotopes - atoms of element have different numbers of neutrons (different masses)

  • Element exists as a mixture of isotopes.

  • Radioactive isotope (carbon-14) -  nucleus decays spontaneously and gives off energy.

Radioactive tracers are common in medical testing.

  • Positions around nucleus - electron shells or energy levels.

    • Moving away from the nucleus increases energy levels.

  • The electron absorbs energy as it moves away from the nucleus.

    • Gives off energy as moves closer to the nucleus.

Bonding:

  • Atoms share or transfer electrons (bonding)

    • Atoms held together by electrons they share or transfer.

  • Covalent bonding - pair of electrons shared.

    • 2+ atoms held together by covalent bond = molecule

      • Electrons shared equally - nonpolar.

Electrons closer to 1 atom – polar (1 atom more electronegative than other). Creates slight charge on atoms.

  • Ionic bonds - 1 atom donates electrons to other atom - form compounds (i.e. salt).

  • Ionic and covalent bonds - strong.

  • There are weaker bonds that exist briefly.

  • Hydrogen bonds form when H+ atom covalently bonds to one atom but attracted to another atom.

Occurs mostly with O2 (like in water).

Reactions:

  • Chemical reaction - making and breaking of chemical bonds.

  • Starting materials – reactants;  ending materials - products.

  • Concentration of reactants determines how fast or slow reaction will go.

Cohesion and Adhesion:

  • Water molecules stick because of hydrogen bonding (cohesion)

  • Water molecules stick to other substances (adhesion)

  • Both responsible for the water’s ability to travel up plants.

Heat

  • Movement = kinetic energy (energy of motion)

    • When it’s motion of atoms/molecules - thermal energy

  • Temperature - average kinetic energy of molecules in matter.

  • Heat - transfer of energy from one object to another.

    • Can be measured in calories.

Specific heat - amount of heat absorbed or lost for 1 g of substance to change temperature 1o C.

  • Water - high specific heat.

  • High heat of vaporization (amount of heat  liquid must absorb for 1 g to be converted to gas)

  • Water has high heat of vaporization because weak hydrogen bonds must break to go from liquid to gas.

pH

  • Water breaks into hydroxide ions (OH-) and hydronium ions (H3O+)

  • pH - measure of the concentration of OH- and H+ in solution.

Increased H+ - more acidic; increased   OH- - more basic.

  • pH scale - 0 (most acidic) to 14 (most basic).

  • Stomach acid - pH of 2 (same as lemon juice); oven cleaner - pH around 13.

  • As concentration of H+ increases, pH decreases.

  • Neutral pH - 7 (pure water)

Buffers:

  • Buffers resist changes in concentrations of (OH-) and H+

  • Buffers in blood help keep pH of blood close to 7.4.

  • If pH rises above 7.7 or below 7, person will not survive.

  • Buffers prevent this.


Importance of pH:

  • Rain not contaminated has pH around 5.6.

  • Because of wastes in atmosphere (from burning fossil fuels and pollution), acid precipitation can result (pH less than 5.6)

Acid precipitation can damage aquatic life and change soil chemistry.