Why are cold solvents preferred during recrystallization and when is recrystallization selected vs other purification techniques?
In: Chemistry
In some materials the relationship between stress and strain during plastic deformation is given by σ = σy+ K(ε − εy) n where K and n are constants. What is the energy absorbed by the specimen during plastic deformation in a tensile test if the material yields at a strain of εy and fails at a strain of εf?
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How do potassium sorbate and benzoate kill yeasts and molds? Would they impart an off-flavor in food?
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Suppose you have an organic sample X that is somewhat soluble in water, even though it is
somewhat more soluble in dichloromethane or ether solvents. But if you do a single
extraction, you get only 60% of your material to transfer from the water to the organic layer.
a) How many “washes” would it take to extract over 90% of your organic material from
the water layer?
b) In this case, would it be better to extract with dichloromethane or with ether?
Assume you changed the solvent to ethyl acetate which has a KD for caffeine of 10. How much caffeine would you extract after three extractions? Show your work.
In: Chemistry
Discuss the microstructure of polymers based on the geometrical structure.
In: Chemistry
1-1Based on the Gibbs free energy of formation of substances listed in the table below, calculate EMF for the following cells:
(i) Zn | Zn2+ (1.0 M) || H+ (1.0 M) | O2 (1 atm) | Pt
(ii) Zn | Zn2+ (1.0 M) || Cu2+ (1.0 M) | Cu
(iii) Pt | H2(g) (1 atm) | H+ (1.0 M) || H+ (1.0 M) | O2 (1 atm) | Pt
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Substances DGfo/ kJ mol-1 (298 K)
_______________________________________________
Zn2+(aq) -147.0
ZnO(s) -318.3
Mn2+(aq) -228.3
MnO4-(aq) -447.3
MnO2(s) -465.2
Mn2O3(s) -881.15
OH-(aq) -157.2
H2O(l) -237.1
Cu2+(aq) +65.52
Cu+(aq) +50.0
Fe3+(aq) -4.6
Fe2+(aq) -78.87
Cr3+(aq) -197.05
CrO42-(aq) -727.8
Cr2O72-(aq) -1301.2
Ce3+(aq) -672.0
Ce4+(aq) -533.06
Ag+(aq) +77.12
AgCl(s) -109.8
Cl-(aq) -131.3
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In: Chemistry
Calculate delta H for the reaction H(g) + Br(g) = HBr(g), given the following information:
H2(g) + Br2(g) = 2HBr(g) delta H = -72 kJ
H2(g) = 2H(g) delta H = +436 kJ
Br2(g)= 2Br(g) delta H = +224 kJ
In: Chemistry
Which of the following reactions is unique to the process of glycolysis?
a. fructose-1,6-bisphosphate ====> glyceraldehyde-3-phosphate + dihydroxyacetone phosphate
b. 2-phosphoglycerate =====> 3-phosphoglycerate
c. glucose-6-phosphate =====> fructose-6-phosphate
d. phosphoenolpyruvate =====> pyruvate
In: Chemistry
In: Chemistry
Discuss the IMF of caffeine used in a TLC experiment with 1:1 Hexanes / Ethyl acetate as the solvent system and explain why the polarity of caffeine is high or low in this solvent?
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At 500 °C, cyclopropane (C3H6) rearranges to propene (CH3CH=CH2):
C3H6 (g) ------> CH3CH=CH2 (g)
The reaction is first order and the rate constant is 6.7 x 10-4 s-1. (a) What is the rate law for the reaction, and; (b) if the initial concentration of C3H6 is 0.100 M, what is the concentration of cyclopropane of after 20 min?
3. Butadiene (C4H6) reacts with itself at 250 °C to form a dimer with the formula C8H12.
2 C4H6 (g) ----> C8H12 (l)
The reaction is second order in C4H6. (a) What is the rate law for the reaction, and; (b) if the rate constant is 4.0 x 10-2 M-1.s-1, and the initial concentration of C4H6 is 0.200 M, how long will it take for the concentration of C4H6 to reach 0.04 M?
4. a) In Q. 2 above what is the half life for the reaction and what is concentration of C3H6 after 3 half-lives b) In Q. 3 above how long are the first and second half-lives?
help with question 2, 3 and 4. i already did them, i just want to compared answers so please show steps.
In: Chemistry
Complete the definitions
chirality
litmus neutrality
insoluble complexes
oxidation of methyl ketones
hemiacetals
acetals
hemiketals
ketals
hydrolysis of ketals
In: Chemistry
Alginate and Calcium Chloride make spheres possible through
spherification.
Can you explain this process and talk about how the concentration,
dropping height, and rate matters?
I'll appreciate as many details as you can say :D
Also, I'm curious to know if there is an alternative to create this
spheres with other reactants.
Thank you so much!
In: Chemistry
A 25.0 mL sample of 0.100 M barium chloride reacts with 40.0 mL of a 0.200 M lead (II) sulfate solution to form barium sulfate and lead (II) chloride.
A) Write the balanced equation.
B) How many grams of lead (II) chloride will form?
C) If you make 0.560 grams of lead (II) chloride from this reaction in the lab, what is the percent yield?
D) How many grams of excess reagent are left over?
In: Chemistry
1) Constant-volume calorimeters are sometimes calibrated by running a combustion reaction of known ΔE and measuring the change in temperature. For example, the combustion energy of glucose is 15.57 kJ/g. When a 2.500 g sample of glucose burns in a constant volume calorimeter, the calorimeter temperature increases from 21.45 to 23.34°C. Find the total heat capacity of the calorimeter (in kJ/K).
2)An electrical heater is used to add 18.25 kJ of heat to a constant-volume calorimeter. The temperature of the calorimeter increases by 3.40°C. When 2.25 g of ethanol (C2H5OH) is burned in the same calorimeter, the temperature increases by 12.45°C. Calculate the molar heat of combustion for ethanol (enter in kJ).
3)A 0.90 g sample of caffeine, C8H10N4O2, burns in a constant-volume calorimeter that has a heat capacity of 7.85 kJ/K. The temperature increases from 298.25 K to 303.34 K. What is the molar heat of combustion of caffeine (in kJ).
4)Use standard enthalpies of formation to determine ΔHorxnfor:
2Al(s) + 3Cl2(g) → 2AlCl3(s) Find the change in internal energy for this reaction. Enter in kJ.
5)Use standard enthalpies of formation to determine ΔHorxn for:
2NH3(g) + 3O2(g) + 2CH4(g) → 2HCN(g) + 6H2O(g) Find the change in internal energy for this reaction. Enter in kJ.
In: Chemistry