Chem 1510 Lab Exam #2

expected number of unpaired electrons in KMnO4

0

enthalpy of ionization of acetic acid

= -enthalpy of R1 + enthalpy of R2 where R1 is the reaction of HCl and NaOH and R2 is the reaction of acetic acid and NaOH

16.04x10^-24 J/T

= 1.73(9.274x10^-24 J/T) = 1.73 Bohr magnetons

1 atm

= 101.315 kPa

R

= 2.18x10^-18J/hc = 10967758.1 m^-1

current(A)

= Coulomb (C)/second (s)

volt(v)

= Joules (J)/Coulomb (C)

Why can't we determine the enthalpy of acetic acid ionization in water directly?

1. Our starting reagent is aqueous HC2H3O2 which means it is already dissolved in water 2. Even if pure acetic acid were to be added to water, this would not work because this reaction would not go to completion

Curie temperature of gadolinium

20.1 C

If there is a leak in the wash bottle cover, how will this affect the mass of NaHCO3 in a tablet?

A leak through the wash bottle cover would have no effect on the mass of NaHCO3 in the tablet. This mass is found by multiplying the % mass by the mass of the tablet, and neither of these values are affected by the volume of water forced out of the wash bottle.

volume magnetic susceptibility (Xv)

ratio I/H where I is the induced magnetic field due to alignment of spins and external field of strength H

enthalpy of fusion of ice

C(ice).mass(ice).delta T(ice) + mass(ice).delta H(fusion) + C(water)+m(water from ice).delta T(water from ice) + C(water).mass(water).delta T(water) + S(styrofoam).delta T(water) = 0 where C(ice) = 2.06 J/gC S(styrofoam) = 46.7 J/C

specific heat capacity of aluminum

C(metal).mass(metal).delta T(metal) + C(water).mass(water).delta T(water) + 23.7(J/C).deltaT(water) = 0

Lab 8 Mass NaHCO3 in an Alka-Seltzer Tablet, Density and Molar Mass of CO2 and the Ideal Gas Constant Objectives

Determine mass NaHCO3 in an Alka-Seltzer tavlet, determine density of CO2 (g), determine molar mass of CO2, determine the ideal gas constant

when heat is added to a substance in a given phase

KE increases, delta PE = 0

when a phase change occurs

KE remains the same and the PE changes

NaHCO3 and HCl reaction

NaHCO3 (aq) + HCl (aq) --> NaCl (aq) + H2O (l) + CO2 (g)

pressure of CO2 produced by the alka-seltzer tablet

P(outside) + 0.9 kPa

linearity

Sm is less than 5% of m and R^2 is > 0.97

temperature change with a phase change

delta KE and PE change

Lab 9 Calorimetry I Objectives

determine Specific Heat Capacity of Water, Specific Heat Capacity of Aluminum & Enthalpy of Fusion of Ice

ni is less than nf

false

ferromagnetic

have domains in which the magnetic moments are aligned and upon application of an external field there is more perfect alignment of the spins compared to paramagnetic substances

sodium

is not paramagnetic because the 2s1 electrons are involved in bonding with other sodium atoms and in metallic bonding electrons are paired

thermodynamics

study of the energy changes that accompany chemical and physical transformations

diamagnetic

substances with no unpaired electrons, decrease the strength of the magnetic field (lines get further apart)

ni and nf are integers

true

gas constant R

0.08206 L.atm/K.mol

expected number of unpaired electrons in CuSO4 5H2O

1

the lowest electronic energy in the hydrogen atom is 2.18 x 10^-18 J

false

to test hypothesis that nf=1, ni must start at 3

false

Examine the hydrogen emission spectrum. Which wavelength has the most intense emission? Which ni and nf values are associated with this emission?

91.2 nm has the most intense emission. This is the shortest wavelength on the hydrogen emission spectrum, and energy is inversely proportional to wavelength. The ni and nf values that are assocaited with this emission are 1 and ∞.

specific heat capacity of water (Cw)

= ((voltage.current.time) - 25.7(J/C).delta T)/(mass of water.delta T)

1/lambda

= (R/nf^2) - (R/ni^2)

delta E

= -2.18x10^-18 J((1/nf^2)-(1/ni^2)) = hv = hc/lambda = hc((R/nf^2) - (R/ni^2))

En

= -2.18x10^-18 J/n^2 = -hcR/n^2

Curie's constant C

= XmT(K)

magnetic susceptibility Xm (cm^3/mol)

= Xv/packing efficiency = 1.0x10^-9(M.L.C/m)(R-R0) where L is length of tube, C is the calibration constant, R is reported by the magnetic susceptibility balance, R0 is reported with an empty tube

molar mass

= dRT/P (d is calculated from mass of CO2 and the volume of water forced from the wash bottle)

1 Bohr magneton

= eh/(4(pi)m) = 9.274x10^-24 J/T = sqrt(8XmT) = sqrt(8C) = sqrt(n(n+2)) where e is the charge on the electron, h is Plancks constant, m is the mass of the electron, and T is the magnetic field

enthalpy of base hydrolysis of NH3

= enthalpy of R1 + enthalpy of R3 where R1 is the reaction of HCl and NaOH and R3 is the reaction of HCl and NH3

IE from nf

= hc/lambda.inf = hcb

IE where nf > 1

= hcb + hcR((1/1^2)-(1/nf^2))

Ccal

= input energy rate (J/s)/Slope (C/s) = voltage.current/slope

q when there is a phase change

= m(delta H)

moles (n)

= mass / molar mass

q when a substance changes temperature

= mc(delta T)

delta H (per mol H2O formed)

= q (reaction)/mols NaOH = Ccal.delta T/[NaOH].L(NaOH)

delta H(system)

= q(system) = - q(surrounding)

nf

= sqrt(R/b) = sqrt(-m/b)

energy output rate (Watts) (J/s)

= voltage * current

Henry's Law constant k

=[CO2 (aq)]/P

initial energy level (ni)

> nf (for emission)

Based on your mass of NaHCO3 in a tablet, calculate the mass of citric acid needed to ensure that NaHCO3 is the limiting reagent in Reaction 1.

(From Run 1) 1.67 g NaHCO3 *(1 mol NaHCO3/84.01 g) = 0.0198785859 mol NaHCO3, 0.0198785859 mol NaHCO3*(1 mol H3C6H5O7/3 mol NaHCO3) = 0.0066261953 mol H3C6H5O7, 0.0066261953 mol H3C6H5O7*(192.14 g/mol H3C6H5O7) = at least 1.273157165 or more g H3C6H5O7

Lab 11 Enthalpies of Neutralization and Ionization Objectives

1. Perform electrical determination of the calorimeter constant (Ccal) to more accurately determine the enthalpies of neutralization of three acid base reactions 2. Apply Hess's law to determine enthalpies of reactions that are not possible to determine experimentally

factors that affect Xv

1. number of unpaired electrons per unit atom or ion (what we're looking for) 2. packing efficiency 3. temperature increases tendency to randomize which decreases Xv

Lab 10 Hydrogen Atomic Emission Spectroscopy, Magnetic Susceptibility and Number of Unpaired Electrons Objectives

1. record emission wavelengths of hydrogen in the visible region using a hydrogen discharge tube 2. using your emission wavelengths data, determine the applicable nf value, the Rydberg constant and assign transitions for each observed emission line 3. calculate and raw electronic energy level diagram for the hydrogen atom and calculate the hydrogen atom ionization energy 4. using a magnetic susceptibility balance, determine the number of unpaired electrons in MnSO4.H2O(s) and ZnSO4.H2O(s)

Pressure is directly proportional to

1/V

expected number of unpaired electrons in MnO2

3

citric acid and NaHCO3 reaction

3NaHCO (aq) + H3C6H5O7 (aq) --> Na3C6H5O7 (aq) + 3H2O (l) + 3CO2 (g)

expected number of unpaired electrons in MnSO4 H2O

5

Curie temperature of iron

770 C

Consider resonance and bond strength, explain why one reaction is more exothermic than the other.

According to the lab manual, only the acetic acid exhibits resonance. Species that exhibit resonance are more stable so the reaction involving acetic acid should be more exothermic than it would otherwise be. However, our results indicate that the reaction that did not include acetic acid, the hydrolysis one, was actually more exothermic, so this is interesting.

We desire perfect insulation; however we do not quite achieve it. How does imperfect insulation affect Tf in the specific heat capacity of aluminum experiment?

Again, if there is imperfect insulation then some of the heat from the hot metal will escape. That means the final temperature when it reaches equilibrium will be less than it should be. Therefore, delta T will be less than it should be, HOWEVER the magnitude of the change in temperature of the aluminum is greater. This value is in the denominator when solving for the specific heat of aluminum, therefore if it is greater, then we will find a smaller specific heat value.

What errors mostly affect the specific heat capacity value: errors in measurements of mass or errors in measurements of temperature? Explain your reasoning.

Errors in measurements of temperature mostly affect the specific heat capacity value. Change in temperature is used more times than mass in each equation, which would skew the results more each time the value was used. Also, change in temperature requires more exact measurements because a slight difference can cause a large change in magnitude.

What quantum numbers control the electronic energy in the hydrogen atom? What quantum numbers control the electronic energy in the sodium atom?

For hydrogen, the quantum numbers n=1, l=0, ml=0, ms=+1/2 control the electronic energy in the atom. For sodium, the quantum numbers n=3, l=0, ml=0, ms=+1/2 control the electronic energy in the atom.

What conditions can be expected to lead to more ideal gas behavior? Consider pressure and temperature.

Generally, a gas behaves more like an ideal gas at higher temperature and lower pressure, as the potential energy due to intermolecular forces becomes less significant compared with the particles' kinetic energy, and the size of the molecules becomes less significant compared to the empty space between them.

without an external field

H = 0, magnetic spin direction is random

with an external field

H > 0, most magnetic spin moments align and the substance is magnetized, net magnetization is I

acetic acid ionization reaction in water

HC2H3O2 (aq) + H2O (l) --> H3O+ (aq) + C2H3O2- (aq)

Which of the three hypothesis fits the Rydberg equation? Explain your choice.

Hypothesis #2, that nf=2, fits the Rydberg equation. This is because a plot of 1/λ vs. 1/ni2 is linear. We know it would be linear because the R^2 value is extremely close to 1, at 0.999658582. The difference between nf calculated and nf assumed is also less than 0.01, so the values are close enough to say they are pretty much equal.

If a student notes that some of the solution spills after the reaction. If the student continues with the heating phase, how will this affect the results?

If a student spills some of the solution, the heating slope will be steeper than it should be. Q = mc(delta T), so if the same amount of electric energy is used to heat the solution (Q is constant), the specific heat of the solution (c ) is constant, and the mass of the solution has decreased (m), then delta T must increase. The expected effect would be intermediate to large depending on how much water is spilled, and the error is random if this spill only occured one time.

According to Henry's Law (you will learn about this in the next week or so), some CO2 remains in test tube HCl solution. For this question assume the CO2 that dissolves in the water in the wash bottle is negligible. How is this expected to affect the density of CO2?

If some carbon dioxide is still in the HCl solution, the difference between the mass of of the reaction system and the mass of the product system will be less, so the calculated mass of carbon dioxide produced will be less. Density is equal to mass/volume. Mass is the numerator in the equation for density, so if you decrease mass, density will decrease.

According to Henry's Law (you will learn about this in the next week or so), some CO2 remains in test tube HCl solution. For this question assume the CO2 that dissolves in the water in the wash bottle is negligible. How is this expected to affect the gas constant R?

If some carbon dioxide is still in the HCl solution, the difference between the mass of the reaction system and the mass of the product system will be less, so the calculated mass of carbon dioxide produced will be less. Converting a smaller mass of carbon dioxide to moles of carbon dioxide will result in a smaller amount of moles of carbon dioxide. R is equal to (voume*pressure)/(temperature*moles). Moles are in the denominator in the equation for R, so if you decrease moles, R will increase.

If there is a leak in the wash bottle cover, how will this affect the density of CO2?

If there is a leak through the wash bottle cover, there will be pressure loss because the CO2 will escape through the leak. If there is pressure loss, there will be less pressure to force water out of the wash bottle, resulting in a lower volume of water produced. Density is equal to mass/volume. Volume is the denominator in the equation for density, so if you decrease volume, density will increase.

If there is a leak in the wash bottle cover, how will this affect the gas constant R?

If there is a leak through the wash bottle cover, there will be pressure loss because the CO2 will escape through the leak. If there is pressure loss, there will be less pressure to force water out of the wash bottle, resulting in a lower volume of water produced. R is equal to (volume*pressure)/(temperature*moles). Volume is in the numerator in the equation for F, so if you decrease volume, R will decrease.

We desire perfect insulation; however we do not quite achieve it. How does imperfect insulation affect Tf in the specific heat capacity of water experiment?

If there is imperfect insulation, some of the heat generated by the electrical heater will escape. That means the final temperature will be less than it should be, and therefore delta T will be less than it should be. In the equation we used to find the specific heat of water, delta T is subtracted in the numerator. So, if we are subtracting a smaller number from the numerator, the numerator will be greater than it should be. Delta T is also part of the denominator, so we are dividing the overall answer be a smaller number as well. If the numerator is greater and the denominator is smaller, both of these factors will help to increase specific heat.

We desire perfect insulation; however we do not quite achieve it. How does imperfect insulation affect Tf in the enthalpy of fusion of ice experiment?

If there is imperfect insulation, then some heat from the surroundings will leak into the ice/water system and the final temperature will be greater than it should be. The change in temperature of the ice is not effected because it only depends on the initial temperature of the ice and the melting point. The magnitude of the change in temperature of the water from the ice will be greater if the final temperature is greater than it should be because the initial temperature is zero. The magnitude of other temperature changes of the water will be less because if the final temperature is greater, there will be less of a difference between the initial and final temperatures of the water. The change in temperature with a greater magnitude is negative, and the changes in temperature with lesser magnitude are positive, so overall there is a greater negative number, so the enthalpy of fusion is LESS than it should be. This explains why our average enthalpy of fusion was about 12% less than it should have been.

According to Henry's Law (you will learn about this in the next week or so), some CO2 remains in test tube HCl solution. For this question assume the CO2 that dissolves in the water in the wash bottle is negligible. How is this expected to affect the molar mass of CO2?

Molar mass will also decrease. As explained above, density will decrease. Molar mass is equal to (density*R*temperature)/pressure. Density is in the numerator in the equation for molar mass, so if you decrease density, molar mass will decrease.

If there is a leak in the wash bottle cover, how will this affect the molar mass of CO2?

Molar mass will also increase. As explained above, density will increase. Molar mass is equal to (density*R*temperature)/pressure. Density is in the numerator in the equation for molar mass, so if you increase density, molar mass will increase.

R2: molecular, overall, and net ionic equation for acetic acid (aq) and NaOH (aq)

Molecular: HC2H3O2 (aq) + NaOH (aq) --> H2O (l) + NaC2H3O2 (aq) Overall: HC2H3O2 (aq) + Na+ (aq) + OH- (aq) --> H2O (l) + Na+ (aq) + C2H3O2- (aq) Net: HC2H3O2 (aq) + OH- (aq) --> H2O (l) + C2H3O2- (aq)

R3: molecular, overall, and net ionic equation for HCl (aq) and NH3 (aq)

Molecular: HCl (aq) + NH3 (aq) --> NH4Cl (aq) Overall: H3O+ (aq) + Cl- (aq) + NH3 (aq) --> NH4+ (aq) + Cl- (aq) Net: H3O+ (aq) + NH3 (aq) --> NH4+ (aq)

R1: molecular, overall, and net ionic equation for HCl (aq) + NaOH (aq)

Molecular: HCl (aq) + NaOH (aq) --> H2O (l) + NaCl (aq) Overall: H3O+ (aq) + Cl- (aq) + Na+ (aq) + OH- (aq) --> H2O (l) + Na+ (aq) + Cl- (aq) Net: H3O+ (aq) + OH- (aq) --> 2H2O (l) or H+ (aq) + OH- (aq) --> H2O (l)

With respect to verifying Boyle's law, does it matter what we are using volume in mL (as opposed to L) and pressure in kPa (as opposed to atm)?

No, it doesn't matter. P1V1 = P2V2. If you convert the units on both sides of the equation, then both sides will change by the same factor and therefore will still be equal to each other. Both sides just have to be in the same units.

How well does your ionization energy compare with the literature value of 1.312 x 106 J/mol?

Our ionization energy is pretty close to the literature value. We got 1.32 x 10^6 J/mol, so we were only 0.008 x 10^6 off.

How does your result compare with the literature values of 333 J/g for the enthalpy of fusion? Is it within experimental error (5%)?

Our result was a bit less than the literature value of 333 J/g for the enthalpy of fusion. The enthalpy of fusion came out to be about 292 J/g. 1-(922/333)*100 = 12.31 or approximately 12% error. Not horrible, but could be better.

to determine the mass of NaHCO3 in the alka-seltzer tablet

g CO2 --> mols CO2 --> mols NaHCO3 --> g NaHCO3 --> % mass NaHCO3 --> mass of NaHCO3 in a tablet

According to Henry's Law (you will learn about this in the next week or so), some CO2 remains in test tube HCl solution. For this question assume the CO2 that dissolves in the water in the wash bottle is negligible. How is this expected to affect the mass of NaHCO3 in a tablet?

The Mass of NaHCO3 that produced the carbon dioxide is found by taking the mass of carbon dioxide, converting it to moles, converting it to moles of NaHCO3, and converting moles of NaHCO3 to mass of NaHCO3. This mass is then used to find the % mass of NaHCO3 in the sample, and then the mass of the tablet is multiplied by this % mass to get the mass of NaHCO3 in the tablet. Therefore, if the mass of carbon dioxide is less due to the difference between the mass of the reaction system and the mass of the product system being less, the mass of NaHCO3 will be less.

ideal gas

gas particles have zero volume (or occupy a negligible fraction) and there are no inter-particle attractions

Between the enthalpy of ionization and hydrolysis, which is more exothermic?

The enthalpy of hydrolysis is more exothermic. It is more negative (-86477 kJ) than the enthalpy of ionization (-468 kJ)

relationship between the pressure of CO2 (g) in the headspace and in CO2 (aq)

directly proportional

How does a magnetic susceptibility balance work?

The magnets inside move to a new position to maximize interaction with the magnetized sample. Then a force is applied to bring the magnets back to their original position. A current flows through a circuit to apply the force. Rather than measure a current, a voltage is measured across component resistors, which is directly proportional to the force required to maintain the magnets in their original positions and is a measure of magnetic susceptibility

Would there be a difference in the results if 12 mL HCl(aq) was used in place of 7 mL? Explain.

There would be no difference in the results as long as the HCl did not mix with the water. We needed the HCl to be in excess for the reaction to work anyway.

Consider reactions in which NaOH is the limiting reagent. What is the effect of using 1.20 M acid in place of 1.0 M acid?

There would be no effect of using 1.20 M acid in place of 1.0 M acid. If NaOH is the limiting reagent, then the acid is already in excess. Using higher molarity acid just means more moles of acid if we use the same volume, so it would just be more in excess. The error is small because there is no effect and systematic because it would be because of something we did each time.

What is the effect of using 32 g of water in place of 30 g of water?

This would affect the heat capacity of the solution, as more water would dilute or decrease the molarity of the solution more. For example, the heat capacity of 1 M NaCl is 3.78 J/gC and the heat capacity of pure water is 4.184 J/gC. Adding more water to the solution would likely increase the heat capacity from 3.78 J/gC, bringing it closer to that of water. The expected effect would be small since the water itself is not a reagent. The error is systematic if 32 g was used in place 30 g each time.

What is the effect of a temperature sensor that consistently reads 0.55℃ higher than it should?

This would have no effect. All that matters for the equations to find the enthalpy value is the difference between the initial and final temperature of the solution. If 0.55 degrees is added to both the initial and the final temperature, the difference between them would be the same. This is a systematic error because this sensor would be used each time. The effect is expected to be small because there is no effect.

In the procedure, you are asked to load as much Alka-Seltzer tablet into the gelatin capsule as possible. Why is it advantageous to load a large sample mass compared to a small mass such as 0.020 g?

Using a larger sample mass produces more carbon dioxide than a small mass would. More carbon dioxide gas creates more pressure, forcing more water out of the wash bottle. A larger volume of water is easier to measure than the amount that a sample mass of 0.020 g would have produced.

Lab 7 Gas Laws Objectives

Verify Boyle's Law, determine the Henry's law constant (k) for CO2 (g), and determine absolute zero

What is the least accurately measured parameter, volume or pressure?

Volume. At smaller volumes (or higher pressures) it becomes difficult to hold the syringe at a constant volume against the pressure. We also had to "eyeball" the volume measure on the syringe while the data logger has the technology to measure pressure more exactly.

The autopipette is supposed to be set to 100 units corresponding to 1.00 mL. What is the effect of making measurements with a setting of 96 units but doing the calculations that assume 100 units?

We would be using a volume of 0.96 mL NaOH instead of 1.00 mL, which means we would have less moles of the limiting reagent, or 0.0096 mol instead of 0.01 mol. Moles of the limiting reagent are in the denominator in the equation for the enthalpy value, so decreasing moles of NaOH will increase the enthalpy value. This effect is expected to be intermediate (4-9%). The error is systematic because it would be because of something we did each time.

Based on your results, is P x V a constant? Do your results verify Boyle's law?

Yes, P x V is a constant. All the values in the last column are in the 3700's, and considering these numbers are all above 3000, 16-17 isn't a huge standard deviation. This does verify Boyle's Law because in order for P1V1 to equal P2V2, P x V must be constant.

y-intercept in lab 10

b = R/nf^2 (in m^-1)

mass of CO2 (g)

difference in the mass of the bottle before and after opening it and allowing the pressurized CO2 (g) to leave

first law of thermodynamics

law of conservation of energy

slope of the line in lab 10

m = -R

mass of degassed CO2

mass after CO2 (g) let out - mass after degassing

mass of beverage added to fill bottle

mass after filling - mass after degassing

mass of beverage in beverage bottle

mass after filling - mass of empty bottle

volume of headspace in L

mass of CO2 in headspace / density of pepsi solution in g/mL (divide by 1000 to get L)

mass of CO2 produced in NaHCO3 (alka-seltzer) and HCl reaction

mass reaction system- mass product system

[CO2 (aq)]

mol of degassed CO2/volume of beverage in L

units of Henry's law constant k

mol/(L.atm)

packing efficiency

mol/cm^3 = density/molar mass

electron paramagnetic resonance (epr) spectroscopy

specialized spectroscopy dealing specifically with spin states

paramagnetic

substances with unpaired electrons, increase the strength of the magnetic field (lines get closer together)

Curie temperature

temperature at which a ferromagnetic substance changes state from ferromagnetic to paramagnetic

Why is hydrochloric acid added to the reaction between citric acid and NaHCO3?

to ensure that the acid is in excess and NaHCO3 is the limiting reactant (NaHCO3 will react with HCl first)

How do chemists use the first law of thermodynamics?

to relate observed external changes in energy to equal but opposite internal changes

if the electromagnetic wavelength is known, the energy can be calculated according to the formula hc/lambda

true

long wavelength emission have lower energy compared to short wavelength emissions

true

the Rydberg constant has units of m^-1

true

the highest electronic energy in the hydrogen atom is 0 J

true

the hydrogen atom ionization energy can be determined from consideration of the emission spectrum of the hydrogen atom

true

to test hypothesis that nf=1, plot 1/lambda versus ni^2

true

q(system) = q1 + q2 + q3

where q1 is the energy needed to raise the temp. of the ice from the starting temp. to 0, q2 is the energy needed to melt the ice (no temp. change), q3 is the enregy need to raise the temp. of the water from the ice from 0 to Tf

sodium atom in the gas phase

would be paramagnetic

Specific heat determination of metal as performed in this lab

ΔPE=0, ΔKE<0

Enthalpy of fusion as performed in this lab

ΔPE>0, ΔKE=0