CHEM 105B Lab Exam

What must be held constant when using the initial-rate method?

Temperature

Decomposition of Hydrogen peroxide

2H2O2 --> 2H2O + O2

How are we going to observe the rate of reaction of the decomposition of hydrogen peroxide?

monitoring the amount of oxygen gas produced as a function of time

What is the catalyst used for the decomposition of hydrogen peroxide?

potassium iodide (aqueous)

What is the intermediate in the reaction mechanism of the decomposition of hydrogen peroxide?

IO-, hypoiodite ion

What factors affect rate of reaction?

Reactant concentration, catalyst concentration, phase of the reactants, reaction surface area, and temperature

What is temperature?

Temperature is the measure of the average kinetic energy of particles

J/mol

What is the units for Activation Energy?

What is the equation that shows the relationship between k, temperature, and activation energy

k=Ae^(Ea/RT)

Equation used to find Activation Energy when we know the ratio of the rate constants

ln(k2/k1)=Ea/R(1/T1-1/T2)

What apparatus is used in the decomposition of hydrogen peroxide reaction?

Volumetric analysis, gas collection apparatus

Why do we equalize water in Pipet A and Pipet B?

To ensure that the pressure in the closed system is equal to the atmospheric pressure

Why do we use relative volume?

relative volume is proportional to molarity, while actual volume is proportional to moles; it also takes into account the differences in volume of solution

change in volume/volume of solution

How do you find relative volume?

What do we plot in a graph for the lab with the decomposition of hydrogen peroxide; also what does the slope determine?

Relative volume vs time; slope is the rate of the reaction

What type of error did we calculate for the decomposition of hydrogen peroxide?

error propagation when determining activation energy

How are orders of reactions determined?

Experimentally and through the initial-rate method

colorless

FD&C Blue #1 and a hypochlorite will produce a product that is...

What is Beer's Law and what does it relate?

A=exlxc; it directly relates absorbance to molar concentration

If k in the rate law is small or large how will the reaction proceed?

If the k is small it will be slow, if the k is large it will be fast

zero order: [A]=-kt+[A]o

first order: ln[A]=-kt+ln[A]o

second order: 1/[A]=kt+1/[A]o

What are the integrated rate law expressions?

What does a spectrometer collect?

absorbance vs time

What does a spectrometer collect for our case of this experiment?

the change in amount of dye in the reaction mixture over time

Graphing the integrated rate laws, what does the slope give you in our case of [Blue#1]?

rate constant k'

what form of hypochlorite is used with Blue #1?

NaOCl

Which reaction is used in excess: Blue #1 or hypochlorite?

hypochlorite

what do you call a reaction with a large excess of one of the reactants?

"pseudo" nth order reaction

What is the rate law for Blue#1 and NaOCl

rate=k'[Blue#1], k'=k[OCl-]

volumetric flask

Where do you do a proper dilution?

what spectrometer is used?

visible-near IR spectrometer

what is the linear region of Beer's Law

0.1

what initial concentration is kept constant: NaOCl or Blue #1

Blue #1

use log and graph log(k') vs log (OCl-)

how do you determine the reaction order of OCl- and rate constant k

What is BTB?

bromothymol blue

what is acidic BTB and what color is it and what is the wavelength max?

HB, yellow, 432 nm

what is basic BTB and what color is it and what is the wavelength max?

B-, blue, 616 nm

KH2PO4, potassium dihydrogen phosphate

what makes BTB acidic?

what makes BTB basic?

K2HPO4, potassium hydrogen phosphate

What is the total concentration of BTB?

[BTB]=[HB]+[B-]

linearly, A=AHB+AB-

how do the absorbances of HB and B- add up?

how do you find molar absorptivity of B- at 616 nm?

Beer's Law calibration plot (absorbance vs molarities of B-), using K2HPO4 as a constant

how do you find percent error?

experimental-theoretical/theoretical

what is the formula for the capacity of a buffer?

change in volume/change in pH

How is an acid or base's strength characterized?

degree of dissociation in water

What is the Henderson-Hasselbalch equation?

pH = pKa + log [A-]/[HA]

when is the henderson-hasselbalch equation valid?

within +/- 1 pH unit of the pKa of the acid

what does buffer capacity depend on?

ratio and total absolute concentrations of the conjugate acid-base pair

What is the limiting reactant when preparing a buffer solution?

the strong acid or strong base added

What is the pH sensor an example of?

a galvanic cell

What did we graph to determine the buffer capacity?

Buffer capacity vs pH

what occurs at the equivalence point?

moles of acid and base are equal

what is a polyprotic acid?

dissociation of successive acidic hydrogen ions

what graph did we use to determine where the equivalence point occurs? What are on its axises?

change in volume/change in pH vs mL of base added, Modified Gran Plot

What is the definition of solubility?

the quantity of solute that can dissolve in a given amount of solvent

solute-solvent intermolecular interactions and temperature

what does the solubility of a solid solute in a solvent depend on?

breaking the solute-solute interactions, breaking the solvent-solvent interactions, making the solute-solvent interactions

Enthalpy change has three sets of interactions:

What do we graph to find enthalpy and entropy for the dissolution of calcium hydroxide?

Gibb's free energy vs temperature

%RSD

stdv/average

what is used to measure voltage>

electronic multimeter

what is the purpose of s a salt bridge?

neutralizes the accumulation of charge

how to we write what occurs in a galvanic cell?

line notation

galvanic cells

spontaneous reaction to generate electrical current

electrolytic cell

nonspontaneous reaction need an external electric current

negative, oxidation

anode

cathode

positive, reduction

what is the order of turning on the PSU

voltage control, current control

what is the order of turning off the PSU

current control, voltage control, turn off PSU

galvanic corrosion

metal with more negative reduction potential will go through corrosion more rapidly

distorted and strained crystal lattice becomes anodic and corrodes more rapidly

stress corrosion

what is corrosion influenced by?

electrolytes that transfer electrons

acidic conditions, protons act as electron acceptors

stressed metals

heated portions

anions, PO43-, CrO42-, and OH-

why are transition metals colorful?

split d orbitals

trioxalatocobaltate (III)

pale pink --> blue green when heated

tryglycinatocobalt (III)

violet

tricarbonatocobaltate (III)

green, vigorous bubbling

hexaaquacobalt (III)

blue/teal

tris(1,10-phenanthroline)cobalt III

yellow