CHEM 117 FINAL, Chemistry 117 Final Exam, Texas A&M (TAMU) Chem Lab 117 Final Study Guide

Calibration

Experimental parameters used to relate to fundamental quantities.

Control Experiment

Shows whether or not a result is due to the experimental factor not taken into account.

Reproducible

Multiple trials of several measurements to verify results.

Density of water decreases as temperature increases. (Inversely related)

Graph on Page 5

Mass is conserved in water-water and water-acetone interactions.

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Volume is not conserved in water-acetone interactions. Water and acetone interact in such a way to reduce volume.

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Calculations for Experiment 1:

Vpipet=Mwater/Density(water)

Vpipet,avg=(Summation of Vpipets)/(# of pipets)

Deviation=(Vpipet-Vpipet,avg)

Electrolytes

Dissociate in solution to form ions that allow the solution to conduct electricity. A weak electrolyte dissociates poorly in solution while a strong electrolyte completely dissociates.

Strong electrolyte examples: NaCl, CaCl2, HCl

Weak electrolyte examples: CH3COOH, tap H2O

Nonelectrolyte

A nonelectrolyte does not dissociate in solution and therefore does not conduct electricity.

Nonelectrolyte examples: CH3OH, distilled H2O

Acid-base reaction

Reaction of an Arrhenius acid (H+) with an Arrhenius base (OH-) that results in neutralization to produce water (H2O).

Titration

A reaction that involves adding a known amount of one solution to an unknown amount of another solution in which the volumes of each solution are measurable and the concentration of the acid known.

Equivalence Point

Point at which stoichiometrically equal amounts of the reactants have been combined.

Precipitate

A solid formed when two liquids are mixed.

What are acid-base indicators?

Indicators are chemicals that change color in the presence of acids or bases. One example is Litmus, in Litmus paper, and is pH sensitive to the presence of acid or base in the reaction. Phenolphthalein is another.

Phenolphthalein

A single, pure compounds that adopts two different structures in acidic and basic solutions.

What is the acid-base reaction done in Experiment 2?

Ba(OH)2(aq) + H2SO4(aq) → BaSO4(s) + 2H2O(l)

What is the acid in the reaction? The base? The precipitate?

Acid: H2SO4 Base: Ba(OH)2 Precipitate: BaSO4

Calculations for Experiment 2:

Concentration (Molarity, M) = moles/volume (in L)

Pressure

Force per unit area. Units include: atmosphere, kilopascal, pounds per square inch, etc.

Volume

Amount of space a substance occupies. Units include: liters or cubic meters

Temperature

Measure of how hot or cold a substance is. Units include: Celsius or Kelvin

Empirical Laws

An equation that describes the relationship of a particular set of variables that is not based on a real model behavior.

Boyle's Law

k = PV

k: The constant ratio (the proportionality constant)

The relationship between pressure and volume is inversely proportional.

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The relationship between pressure and temperature is directly proportional.

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Nano

A factor of 10^-9. One nanometer is equal to one billionth of a meter.

Reducing Agent

Oxidizes metal ions to metal nanoparticles.

M+(aq) + e- →M0(s)

What happens at the reducing step?

Sodium borohydride reduces the silver.

What happens at the oxidation step?

The etching agent reoxidizes the metal on less stable surfaces of the metal ion in order to ensure the most stable shape and size of nanoparticles.

What is the complexing agent used in this experiment?

NaBr

Transmittance

Ratio of light intensity that passes through the solution to the light intensity that passes through a blank sample, Io.

Molar absorptivity

Property of the solute, known as ε

Beer's Law

A = εbc

Stages of Nanoparticle Synthesis

-Nucleation: the sub-nanometer sized particle grows from a few bonded atoms to the point where the atomic arrangement begins to resemble the arrangement in the final nanoparticle

-Growth: particles grow to final size

What is the region of visible light?

Between 400 and 700 nm

If red light is absorbed, what color(s) are being observed?

Green, red light reflects blue and yellow light. (Color wheel on page 55)

What is the role of sodium borohydride?

It is the reducing agent.

Calculations for Experiment 3:

% T = I/Io x 100

A = -log T = -log I/Io = log Io/I

A = 2 - [log % T]

A = εbc

Moles = Volume (in L) x Molarity (M)

The interactions between molecules is dictated by what?

Molecular shape

What is molecular shape derived from?

Bond lengths and geometry of the central atom(s).

DNA intercalation (binding in the ladder)

Molecules that can squeeze between the steps of the DNA ladder that are flat.

"Binding in the Grooves"

Small molecules that can bind into the major and minor grooves of DNA. Typically crescent-shaped.

Valence electrons

Outermost s and p electrons.

Ionic bond

Formed when valence electrons are transferred from one atom to another, effectively creating a cation, X+ and anion, X-.

Covalent bond

Formed when two atoms share a pair of valence electrons.

Difference between polar and nonpolar covalent bonds?

When sharing is equal you get a nonpolar bond. Diatomic molecules are nonpolar covalent bonds. When there is no sharing, you get a polar covalent bond. CO2, CF4, H2O are examples.

Dipole

A separation in charge along a bond.

Electronegativity

The relative tendency of an atom to attract electrons to itself when chemically combined with another atom.

What element is the most electronegative?

Fluorine is the most electronegative element. (refer to Table 1, Page 84)

Octet rule

Rule for drawing Lewis dot structure. Atoms require 8 electrons to fill their outermost s and p orbitals.

What is an expanded valence? Name one element that has an expanded valence.

An expanded valence is when an element can exceed 8 or more electrons. Phosphorus is an example.

What are non-bonding electrons called?

Lone pair electrons

Polyatomic ions

Covalently bonded atoms in which there is an overall charge. Examples: S04^2, CO3^2-, OH-

VSEPR theory

Can be used to describe the three-dimensional structure around the central atom in a Lewis dot structure

Intermolecular forces

Noncovalent interactions between molecules

London dispersion forces

Weakest intermolecular force. Example: CH4

Dipole-dipole forces

Example: HCl

Hydrogen bonding

Not a "real bond" but formed when a hydrogen approaches an electronegative atom. Example: H2O

Polarizability

Used to describe the extent to which an external electric field can distort the charge distribution in a molecule

What are the partial charges on H2O?

Partial positive on H, partial negatives on O.

What are alkanes? Alcohols? Which has stronger intermolecular forces? Why?

Alkanes are hydrocarbons.

Alcohols have a carbon atom bonded to an -OH group. Alcohols have stronger intermolecular forces because of hydrogen bonding.

Is vapor pressure dependent on temperature?

True

What happens to vapor pressure at higher temperatures?

At higher temperatures, kinetic energy increases, which increases the percentage of molecules with sufficient energy to overcome intermolecular attractions and exist in the vapor state.

In the chemicals used in Exp. 9, which had H-bonding?

All the alcohols had H-bonding.

Which liquid had a larger vapor pressure at room temperature? Methanol or ethanol? Why?

Methanol had the higher vapor pressure. Methanol (H3C-OH) is quite polar with H-bonding, as is Ethanol (CH3CH2-OH). What sets the two apart is the fact that ethanol has a greater molecular surface area for London-dispersion forces.

Calculations for Experiment 9:

ΔT = Tf-Ti

T in C + 273.15 = T in K P1/T1 = P2/T2

Vapor pressure = measured - corrected

First Law of Thermodynamics

The total energy of the universe is a constant and cannot be created nor destroyed, merely

converted into another form.

Enthalpy change

The heat flow per mole compound.

What is the difference between ΔH and ΔH◦?

ΔH◦ is molar enthalpy.

What is a state function? Give an example.

A state function is independent of the path from initial to final state. Enthalpy is a state function.

Fill in the blank: The reaction done in Exp. 10 is an application of ____'s Law?

Hess.

What are m and n?

The orders of the reaction with respect to each reactant.

What is activation energy?

Minimum energy needed for molecules to collide.

What does the addition of a catalyst to a reaction result in? Does this speed or slow the reaction?

Addition of the catalyst lowers the activation energy, or barrier. It speeds up the reaction.

What is the stoichiometry of Na2S203 to I2?

2 to 1.

What does a double arrow symbol indicate?

That a reaction can proceed in either direction.

Define equilibrium constant.

Indicates whether the equilibrium is reactant or product favored.

Define Le Chatelier's principle.

The principle that if any change is imposed on a system that is in equilibrium then the system tends to adjust to a new equilibrium counteracting the change.

What is the purpose of the standard solution?

To compare against the experimental values.

Define polymer.

Class of macromolecules with structures built up by repetitive bonding of many smaller molecules called monomers.

Define homopolymer and copolymer.

Homopolymers - one type of monomer. Copolymer - two or more monomer units.

What is the organic polymer made in Exp. 15?

Polypyrrole.

Electrochemical reactions that involve the transfer of electrons between reacting species are called __________.

Redox reactions.

What anion was used in this experiment?

Sodium dodecylbenzene sulfonate.

What is n?

Represents the number of pyrrole molecules in the polymer.

What is the relationship between conductivity and resistivity?

Inversely related.

What is the relationship between temperature and conductivity?

Conductivity decreases as temperature increases.

Was the polymer a conductor or semiconductor? Why?

Semiconductor. As conductivity increased, so did temperature.

Thermochemistry

The study of relationships between chemistry and energy

Energy

The capacity to do work

Work

the result of a force acting through a distance

Heat

the flow of energy caused by a temperature difference

Kinetic energy

the energy associated with the motion of objects

Thermal energy

the energy associated with the temperature of objects (type of KE)

Potential energy

the energy associated with the position or composition of an object

Chemical energy

the energy associated with the relative positions of electrons and nuclei in atoms and molecules (type of PE)

Law of Conservation of Energy

"Energy can be neither created nor destroyed"

System

The object that holds the reaction in question

Surroundings

Everything with which the system can exchange energy

Equation of Kinetic Energy

KE=.5mv*v