Atomic Theory/Moles/Mass Spectroscopy/Molarity

3 subatomic particles

protons - inside nucleus, +1 charge. assigned mass is 1amu.

neutrons - inside nucleus, no charge, assigned mass is 1amu, heaviest particle

electrons - outside nucleus, -1 charge, assigned mass is 0amu.

Atomic Notation

a nuclide of an atom is written with A, Z, and atomic symbol.

• A represents the mass number (protons + neutrons)

• Z represents the number of protons.

• Electrons = protons

• electrons are not in mass number because has an assigned mass of 0.

Isotopes

• atomic variables of an element.

• atoms of the same element, which implies same number of protons and electrons, but the difference is the mass number, which implies a difference in neutrons

• if an element has isotopes, the element’s mass is an average mass of all isotopes and the percentage abundance of each.

• percent abundance = percent of how much that isotope makes up the entire element.

moles

• in chemistry, its the connect between atoms, which have amu, to real life metrics (grams).

• for atoms, 1molof an element = 6.02×10^(23) atoms of that element.

• if you have a molecule or formula unit, and you have mol of this, then you have 6.02 × 10^(23) molecules.

Deflection

the amount each ion is deflected depends on the speed and charge. 

• the faster an ion is moving, the more deflected it becomes.

• higher charge means greater deflection than lower charges.

• the amount an ion is deflected is inversely related to m/z, mass to charge ratio. as I said previously, greater charge lowers the m/z, so it gets deflected more.  lower mass lowers the m/z, so it gets deflected more

relationship between deflection and m/z

• large m/z means less deflection

• small m/z means greater deflection

mass spectrograph

x axis is m/z

• remember: mass = protons and neutrons, a change in the mass of same element atoms means only a change in protons

y axis is abundance of that isotope

relative intensity

if you see this as the y-axis, just add up all the abundances, and divide each abundance by the sum.

Summary of Mass Spectroscopy

• a technique used to find the abundances of isotopes for an element. isotopes of an element are the variations in the atoms of that element, but only in the differences in neutrons. this accounts for the difference in mass numbers. mass numbers are equal to the protons + neutrons, however, protons will never disappear, the only differences are neutrons.

solutions

a homogenous mixture of solute & solvent

• solute is what is being dissolved

• solvent is what is dissolving the solute

concentration

how much solute is dissolved

• however, molarity is way to see concentration because it checks a ratio of solute to solution.

molarity

mols of solute / volume of solution

• increase in temperature increases volume of solution which in terms lower molarity.

• decrease in temperature decreases volume of solution, increases molarity

• units are always mol/L (LITERS)

dilution

increase in solvent, which increases volume, decreases molarity, meaning less concentration per volume.

• volume initial, molarity initial = volume final, molarity final

• the solution before dilution has same solute as after solution. the only thing that changes during a dilution is the volume and molarity.

mixing two solutions

equation: (molarity)(volume) of first solution, + (molarity)(volume) of second solution = (molarity)(volume) of final solution. Volume of final solution is just adding the first two solutions.

solubility

a property that represents the maximum amount of solute in a constant amount of solvent

factors that affect solubility

nature of solute to solvent

• stronger attraction between solute to solvent allow for greater solubility

• ex. zinc chloride vs lead chloride in h20. through ion dipole interactions, the ionic compound is dissolved in the water, however, zinc chloride will have a greater solubility with water. zn ions are smaller meaning they form stronger ion dipole interactions with water.

temperature

• increase in temp of a solution increase the solubility of the solid solute. 

• for gases, solubility decreases as temperature increases because greater kinetic energy

pressure

• changes in pressure does not affect liquid or solid solutes on solubility

• for gaseous solutes, an increase in pressure increases solubility, and a decrease in pressure decreases solubility. gaseous solutes already have much kinetic energy, increase in pressure allows for more interactions with solvent.

rate of solution

how fast the substance dissolves in the solvent

factors that affect solubility

size of particles

• dissolving occurs at the solutes’ surface area, if you have more surface area by breaking the solute into smaller particles, then it will dissolve faster.

stirring

• stirring brings fresh portions of the solute into the solvent, which allows for the solute to dissolve faster.

amount of solute already dissolved

• if you have little solute already in the solution, then dissolving takes place quickly

• if you have lots of solute already dissolved in the solution, then dissolving take time

• insaturated, saturated, super saturated, essentially same has changes in molarity

temperature

• increase in temperature increase the rate of solution only if the solution process is endothermic

• if solution process is exothermic, increase in temperature will not be favored

• gases will increase rate of solution when temperature decreases, and decrease in rate of solution with temperature increases

Heat Enthalpy of Solution Formation

two steps in forming a solution

• separation of solute molecules and separation of solvent molecules

• formation of solute-solvent interactions

first step is always endothermic, adding heat to compromise attractions

• if energy to separation solutes and solvents from each other is greater than solute-solvent energy, then the formation is endothermic

• if heat entalpy of solution is exothermic, that means energy released greater than energy needed

• if heat enthalpy of solution is zero, means ideal solution

density of solution

mass of solution/volume of solution

• always make sure density of solution is g/L.

• density of solution and molarity have one thing in common. the denominator is always volume of solution.