Chemistry/Water Chemistry, Solutions, and pH

Water Facts Water covers 71% of the Earth's surface. Only 3% is freshwater that can be used by living organisms. It is the single most abundant compound in most living things. Water expands when it freezes. In its solid state (ice), it is less dense than in its liquid state (room temperature water). Density of water= 1.0g/L Density = Mass/Volume

The Mickey Mouse Molecule

Shows hydrogen bonds between molecules

Draw TWO water molecules in the space below and show where a hydrogen bond occurs.

• Polarity: When the electrons in a molecule are shared unequally creating a positive side and a negative side to the molecule.

Water is polar because the oxygen atom has a slight negative charge and the 2 hydrogen atoms have a slight positive charge.

Properties

Since water is polar, the slightly positively charged hydrogens in a water molecule and the slightly negatively charged oxygen atom in a water molecule allows for Hydrogen bonding. Hydrogen bonding gives water many special properties. One of them is polarity, which has already been discussed in the previous section.

The next two are Cohesion and Adhesion. Cohesion allows water to attract to other water molecules. This creates surface tension, which helps insects and some spiders to walk on water. Adhesion allows water to be attracted to other substances, like water being attracted to a seed. This causes capillary action, which helps water to flow up into plants.

Water in its solid form is less dense than in its liquid form. This causes ice to float on water (hence, iceburgs), which prevents entire bodies of water from changing to solid. Water also has a high specific heat, which means that water heats slowly and resists temperature change. This is beneficial because it helps keep water temperatures cool for plant life as well as the temperature for all living things on Earth.

Last but not least is that water is the Universal Solvent-- many substances can be dissolved in water.

Mixtures, Solutions, and Suspensions

A mixture, sand

A mixture is a material of two or more elements or compounds that are physically mixed together but not chemically combined.

• Example: Mixing salt and pepper; Sand

A solution is a mixture where a solid is dissolved into a liquid.

Solute: Substance that is dissolved.

Solvent: Substance in which the solute is dissolved

• Example = Koolaid → Powder & Sugar = Solute + Water = Solvent

A suspension is a mixture of water and non-dissolved materials.

• Example = Blood cells and other particles are not dissolved in water.

Acids, Bases, and pH

pH: Indicates the concentration of H+ ions in a solution. The pH of water is 7, which is a neutral pH. This is the chemical equation that shows how water can have a neutral pH:

[H+] + [OH-] → H₂O

Acid: Solution that contains a higher concentration of H+ ions than pure water and has a pH value below 7.

Base: Solution that contains a lower concentration of H+ ions than pure water and has a pH value above 7.

Buffers

The pH of fluids in your body NEEDS to stay between a range of 6.5 - 7.5. If the pH is too low or too high, it will affect the chemical reactions in your body. Buffers are weak acids or bases that react with strong acids or bases to keep pHs within a certain range.