chemistry lab - midterms

Melting point

is the temperature at which its solid form is in equilibrium with its liquid form.

pure crystalline organic substance

has a sharp melting point that melts completely over a short temperature range.

electrostatic forces and intermolecular forces, and size

influence melting point. The stronger the forces that hold each particle, the higher the melting point.

melting point range

can be determined by introducing a finely powdered material in the capillary that is sealed at one end. The capillary is fastened to a thermometer and heated in a well-stirred oil bath.

• temp at which substance begins to liquefy

• temp at which substance becomes completely liquid

ionic bond

hold ions together and is stronger than intermolecular forces and covalent bonds

Intermolecular forces

(London dispersion, dipole-dipole, H-bond) The forces between individual particles. (determines the phase a compound is in at room temperature)

Intramolecular Forces

The forces between atoms or ions inside a compound such as covalent and ionic bonding (determines the stability of a compound)

Ion-Ion Intermolecular Forces

• ionic compounds have strong Intermolecular forces

•  solids at room temperature and they have high m.p.

•  ionic compounds with multiply charged ions generally have higher m.p. than those with singly charged ions

Ion-Dipole Intermolecular Forces

attractive forces between an ion and polar molecule. ex. water and solutes

Dipole–Dipole Interaction

• An intermolecular force that occurs between polar molecules

• Molecules with dipole moments can attract each other electrostatically by lining up so that the positive and negative ends are close to each other

• The greater the polarity of the molecules, the greater the strength of the dipole-dipole interactions

Hydrogen Bonds

hydrogen is covalently bonded to a highly electronegative element of small

atomic size (fluorine, oxygen, and nitrogen). strongest bond.

Dispersion Forces

weak attractive forces that all molecules have. It is the only intermolecular interaction that small, non-polar molecules undergo. (generally gases at room temp.)

Dalton’s postulates

▪ Combination or Synthesis Reaction

▪ Decomposition Reaction

▪ Single Replacement Reaction

▪ Double Decomposition or Precipitation Reaction

Oxidation–reduction (redox)

Chemical reaction in which there is a transfer of electrons from one reactant to another reactant

Nonoxidation–reduction (nonredox)

Chemical reaction in which there is no transfer of electrons from one reactant to another reactant.

oxidized

reducing agent

reduced

oxidizing agent

homogeneous mixture

two or more substances with each substance retaining its own chemical identity

Solvent

Component of a solution that is present in the greatest amount

Solute

Component of a solution that is present in a lesser amount relative to that of the solvent

Solvation or hydration

occurs once solid is separated in to cations and anions, and are surrounded by water molecules.

types of interactions

❑solvent-solvent interaction

❑solute-solute interaction

❑solvent-solute interaction

Saturated

amount of solute dissolved is the maximum that can dissolve [solute] = solubility, no more solute dissolves

Unsaturated

amount of solute dissolved is less than the maximum that can dissolve [solute] < solubility, more solute dissolves

Supersaturated

amount of solute dissolved is more than the maximum that can dissolve [solute] >solubility, becomes unstable and crystals form

Temperature

For most solids and liquids that dissolve in liquids, general rule is that solubility increases with increasing temperature, For gases, solubility in liquids almost always decreases with increasing temperature.

Pressure

Henry’s law - The solubility of a gas in a liquid is directly proportional to the pressure

colligative property

is a property of solutions that depends only upon the number of solute particles, not upon their identity.

❑ vapor-pressure lowering

❑ freezing-point depression

❑ boiling-point elevation

❑ osmotic pressure

Vapor pressure

results from escape of solvent molecules from liquid to gas phase. Partial pressure of gas phase solvent molecules increases until equilibrium vapor pressure is reached

Raoult’s law

when a nonvolatile solute is added to a solvent, vapor pressure of the solvent decreases in proportion to the concentration of the solute

Freezing Point Depression

considering the equilibrium between solid and liquid states. Solute molecules interfere with the rate at which liquid water molecules associate to form the solid state, lowers the freezing point

Boiling Point Elevation

as the temperature at which vapor pressure of the liquid equals the atmospheric pressure, If a solute is present, then the increase in boiling temperature is necessary to raise the vapor pressure to atmospheric temperature

Osmotic Pressure

the movement of solvent from a dilute solution to a more concentrated solution through a semipermeable membrane, Requires pressure to stop this flow

• the area of lower solute concentration to the area of higher solute concentration.

• Movement of solvent from high solvent concentration to low solvent concentration