Organic Chemistry Answers

What is the final product of ethyne with hydrogen bromide

Consider a buffer made up of 0.10 M H2PO4^- and 0.32 M HPO4^2-. The Ka of H2PO4^- is 6.2x10^-8. What is the resulting pH when 1 liter of the buffer is mixed with 0.01 mol HClO4? Assume no change in volume occurs upon addition of the acid.

A. 8.54

B. 6.76

C. 7.66

D. 8.43

A pure white crystalline compound was found to melt at 131.5-132.0oC when taken on a

melting point apparatus, and on further heating, the liquid was found to start bubbling at ca.

155-160

oC. The capillary containing the melted compound was set aside to cool, and

resolidify. When the sample was retried using that same capillary, the sample melted at

120.6-154.5oC, along with some bubbling. What is the cause of the bubbles? Why is the

melting point so wide the second time? Explain by stating what you have learned in this

laboratory about melting points

For the same solid compound as the question above, if the 1 mm sample was heated at 10o

per minute on a melting point apparatus, what would you expect for an approximate

melting point? (note that at this heating rate, the sample will melt rather quickly, but again

give an actual numerical approximation)

1. A vial containing an unknown sample is suspected to be one of the following compounds (mp.): urea (~133 oC), 2,4-dimethylacetanilide (~133 oC), phenacetin (~134oC) or 3-chlorobenzamide (~134 oC). A list of melting points taken on a machine when the 50% of the unknown by volume has been mixed with 50% each of the possibilities is shown in the following table:

2.Three samples labelled R, S, and T possess identical melting points: ~99 oC. When a 75/25 mixture of S and T is prepared, its melting point is 90-95 oC. The melting point of a 50/50 mixture R and T is 79-91 oC. The mp. of a 25/75 mixture of R and S is 97-98 oC. What information does this does this tell you about identity of the 3 compounds? (ie. Which compounds are the same, and which compounds are different? Use only the information you have learned from the slides and your lab manual.) What would you expect as a melting range for a 75/25 mixture of R and T?

What must be the ratio of F- concentration to HF to make a buffer with a pH of 4? pKa = 3.2

a. 0.16

b. 2.4

c. 6.3

d.8.1

If we dissolve CaCO3 in water, we get the following equilibrium:

CO3^2-(aq)+H2O(l) =HCO3^-(aq) + OH^-(aq)

0.675 grams of calcium carbonate is dissolved in enoughwater to make 500 mL of solution. The MW of CaCO3 is 100 g/mol and the Kb of CO3^2- is 2.1x10^-4.

What is the initial concentration of the carbonate ion?

a. 1.35 x 10^-3

b. 0.0135

c. 6.75 x 10 ^-3

d. 0. 021

What is the equilibrium concentration of the hydroxide ion?

a. 6.477 x 10^-4

b. 1.32 x 10^-3

c. 1.5820 x 10^-3

d. 1.9976 x 10^-3

What is the pOH of the solution?

a. 3.1886

b. 2.8794

c. 2.8008

d. 2.6995

What is the pH of the solution?

a. 11.3005

b. 11.1992

c. 11.1206

d. 10.8114

State and draw all the symmetry elements possessed by the 

following molecules' and assign proper point group to them : Allene

C3H6O2

C3H6O2 containing a carboxylic acid functional group

Draw the molecule

A mixture containing C₂H₅Br, HBr, C₂H₆, and Br₂, all at an initial partial pressure of 3.32 atm, is allowed to achieve equilibrium according to the equation below. At equilibrium, the partial pressure of Br₂ is observed to have increased by 0.14 atm. Determine K_p for this chemical equilibrium.

C₂H₅Br(g) + HBr(g) ⇌ C₂H₆(g) + Br₂(g)

a) Find the volume of CO₂ formed at 25 °C and 103 kPa when 0.316 g sodium carbonate is added to 12.0 mL of 0.110 M phosphoric acid.

3 Na₂CO_{3 (s)} + 2 H₃PO_{4 (aq)} −> 2 Na₃PO_{4 (aq)} + 3 H₂O _(l) + 3 CO_{2 (g)}

b) If the leftover amount of excess reactant is thermally decomposed, what volume of gas will be formed at the same conditions as part a)? Show the chemical equation for the decomposition reaction in your answer.