T4 Water and pH Flashcards

Flashcards about water and pH

Importance of Water

Water is essential for life on Earth, as all living organisms are predominantly made of water.

Molecular Structure of Water

H2O, formed by covalent bonds between an oxygen atom and two hydrogen atoms.

Electronegativity and Polarity

Electrons are not shared equally; oxygen is highly electronegative and attracts electrons, making water polar.

Polar Covalent Bonds

Due to unequal sharing of electrons, water molecules have a partial positive end (hydrogen side) and a partial negative end (oxygen side).

Hydrogen Bonding

Interaction between the partial positive charge of one molecule and the partial negative charge of another, causing molecules to clump together.

Hydrogen Bonds

Can form between any polar molecules and are weaker than covalent and ionic bonds individually, but strong in numbers.

Hydrogen Bonds in DNA

Base pairs of DNA strands are held together by hydrogen bonds, which can be easily broken for DNA replication.

Ionic Molecules and Water

Ionic bonds dissociate in water because they attract water molecules, causing polar water molecules to become ordered around the ions.

Electrolyte

Water with ions present that can conduct an electrical charge.

Dissociation of Water

Water molecules sometimes fall apart into hydrogen ions (H+) and hydroxide ions (OH-).

pH Definition

The negative log of hydrogen ion concentration; a pH of 4 has an [H+] of 10^-4.

Acids

pH < 7.0; release or donate H+ ions, which lowers the pH when added to water.

Acids and pH

Acids lower the pH by adding H+ ions to the solution.

Bases

pH > 7.0; release OH- or combine with H+ ions, which increases the pH when added to water.

Bases and pH

Bases increase the pH by releasing OH- or absorbing H+.

Does NaCl Change pH

No, it only changes if a substance with H+ or OH- ions is added.

Neutralization Reaction

Strong acid + strong base → Salt + Water; no change in pH.

Buffers

Compounds that resist changes in pH by absorbing excess H+ or OH- to maintain a certain pH range for cell survival.

Homeostasis

Maintaining a stable internal environment

Unique Properties of Water

Liquid over a wide range of temperature, resistant to temperature changes and state changes, lower density as solid ice, the universal solvent, and exhibits cohesion and adhesion.

Water Resists Temperature Change

Requires breaking H-bonds which needs a lot of energy, helping in temperature homeostasis.

Dissolving in Water

Substances split up into smaller parts and interact with water molecules through hydrogen bonding.

Solutions

Solutions are made up of a solvent and a solute; the solvent dissolves the solute, and dissolved solutes are free to interact with other molecules.

Hydrophilic Molecules

Ionic compounds and polar molecules that dissolve in water.

Hydrophobic Molecules

Non-polar molecules(Oil, fats, gasoline) that do not dissolve in water.

Adhesion and Cohesion

Strong forces of attraction between molecules that allow water to "stick to things."

Serial Dilution

Systematically decreasing the concentration of cells in sample.

Original Cell Density (OCD)

CFU/ (Dilution of sample added to plate * Volume of dilution added to plate)