Lab 1 & 2

Question 1

What was the purpose of the first experiment?

Answer 1

strong acid is reacted with strong base in calorimeter and heat capacity of calorimeter is calculated

Question 2

What is calorimetry?

Answer 2

measurement of the amount of heat evolved or absorbed during a chemical or physical process

Question 3

How does a cold pack with ammonium nitrate work?

Answer 3

NH4NO3 is dissolved in water – endothermic reaction causing the resulting solution to drop in temperature by 20ºC

Question 4

What is the reaction tested for a strong acid and strong base?

Answer 4

HCl + NaOH → NaCl + H2O
–> exothermic reaction

Question 5

What is the surroundings of this reaction?

Answer 5

calorimeter, products of the reaction (water and aqueous salt)

Question 6

What was the calorimeter consistent of?

Answer 6

test tube, stirrer, and a polyethylene foam insulating jacket

Question 7

What is the system of this reaction?

Answer 7

strong acid (HCl) and strong base (NaOH)

Question 8

What is the general reaction of an acid and base?

Answer 8

Net-ionic equation of neutralization where complete ionization occurs:

H+(aq) + OH-(aq) → H2O(l) + heat

Question 9

What is the molar heat of neutralization (∆Hºneutralization)?

Answer 9

-55.84 kJ / mol

Question 10

How can the amount of heat absorbed by the surroundings be measured?

Answer 10

measuring the temperature of the surroundings before and after the reaction

Question 11

How is the final temperature of the reaction taken when the exact instant the reaction ends is unknown?

Answer 11

approximate value by graphing temperature vs time readings and extrapolating back to the instant of mixing: t = 0s –> y-int

Question 12

Is the strong acid or base the limiting reagent?

Answer 12

acid (HCl)

Question 13

What must be done to the probe to ensure a proper reading is done?

Answer 13

wipe with damp paper towel

Question 14

How can you safely increase/decrease temperature of NaOH in the graduated cylinder?

Answer 14

rinse outside with water

Question 15

Where should the stirrer be with relation to the probe inside the graduated cylinder?

Answer 15

probe is inside the ring on the stirrer

Question 16

What is potassiumthiocyanate?

Answer 16

KSCN

Question 17

What is iron(III) nitrate?

Answer 17

Fe(NO3)3

Question 18

What is the reaction of KSCN and Fe(NO3)3?

Answer 18

[Fe(H2O)6]3+ (aq) + SCN- (aq) –> [Fe(H2O)5(SCN)]2+ (aq) + H2O(l)

or

Fe3+(aq) + SCN-(aq) –> Fe(SCN)2+(aq)

Question 19

What are the spectator ions of the reaction?

Answer 19

nitrate ion (NO3-), potassium ion (K+)

Question 20

What is the purpose of this experiment?

Answer 20

to find equilibrium constant of potassiumthiocyanate and iron (III) nitrate and molar absorption coefficient of Fe(SCN)2+

Question 21

How are the equilibrium concentrations determined?

Answer 21

spectrophotometric analysis

Question 22

What is the colour expected for Fe(SCN)2+?

Answer 22

intense yellow/orange colour (even at a very low concentration because they absorb visible light

Question 23

What does the light absorbed amount depend on?

Answer 23

• wavelength of light
• concentration of the absorbing species
• distance the light travels through the sample

Question 24

What is spectrophotometry?

Answer 24

instrumental technique that examines the interaction between electromagnetic radiation (light) and a sample

– amount of light absorbed by the sample at each wavelength is measured

Question 25

What is graphed from the spectrophotometry?

Answer 25

absorbance vs concentration linear graph (directly proportional when wavelength where amt of light is not too small or big)

Question 26

What is the Beer-Lambert Law?

Answer 26

A = εlc

where A is absorbance
ε is molar absorption coefficient in L/mol*cm
l is path length in cm
c is concentration in L/mol

Question 27

What is path length? What is the value in this experiment?

Answer 27

distance the light passes through the sample (1cm - length of cuvette)

Question 28

How are path length and amount of light absorbed related?

Answer 28

directly proportional: longer path length = more light absorbed

Question 29

What is the slope of the absorbance vs concentration graph?

Answer 29

ε x l measured in L/mol

Question 30

What does it mean for the RMSE to be close to 0?

Answer 30

closer the points are to a perfect match for the equation of the line

Question 31

What is the dissociation reaction of Fe(NO3)3?

Answer 31

Fe3+(aq) + 3NO3-(aq)
–> [Fe3+] = [Fe(NO3)3]

Question 32

What is the dissociation reaction of KSCN?

Answer 32

K+(aq) + SCN-(aq)
–> [SCN-] = [KSCN]

Question 33

How will the Fe3+ + SCN- –> Fe(SCN)2+ reaction proceed?

Answer 33

reaction proceeds to the right (product side) and almost ALL the SCN- will react to mean Fe(SCN)2+

Question 34

What does it mean for the concentrations if all of the SCN- reacts?

Answer 34

initial concentration of SCN- = equilibrium concentration Fe(SCN)2+ = x

Question 35

What does the initial concentration refer to?

Answer 35

concentration of the ion after dilution (mixing SCN- and Fe3+ with DI water)

Question 36

What are the conditions necessary for creating samples of Fe(SCN)2+?

Answer 36

SCN- volume < Fe3+ volume

small volumes (1 mL) of SCN- and Fe3+ (for higher absorbance)

volume of water less than 5mL (for higher absorbance)

Question 37

Why must SCN- volume < Fe3+ volume?

Answer 37

avoid precipitation of other species

Question 38

Why are the Fe3+ solutions acidified?

Answer 38

prevent the precipitation of Fe(OH)3