Determination of a Molar Mass by Freezing Point Depression: This experiment used Stearic Acid

Experiments done in many first-year chemistry courses. They often use cyclohexane as the solvent and compounds such as p-dichlorobenzene, biphenyl, and naphthalene as the unknown solutes. Describe the advantages of this experiment over those.

Mass of antacid in sample: 1.5004 g

Antacid tablet: 1.6080 g

Composition of antacid:

Aluminum hydroxide: 160 mg

Magnesium carbonate: 105 mg

Molarity of EDTA: 0.01000 M

Pipet a 10.00 mL aliquot of the antacid sample solution to a 125 mL of Erlenmeyer flask followed by adding about 10 mL of the bicarbonate-carbonate buffer solution (pH 10.0 ± 0.1). Add about 3 mL of triethanolamine (TEA) and swirl the mixture for 2 min. to enhance the formation of Al-triethanolamine complex and to mask the Al-EDTA complexation. Set the solution aside until the turbid solution becomes mostly clear for easy observation of endpoint. Add 5 drops of Calmagite indicator and mix well. The solution should appear wine red color in this moment.Direct-titrate the solution with standard EDTA solution until the color changes to pure blue at the endpoint. The used volume of EDTA was 6.00ml. Hence, in this protocol quick titration will give an ideal result.

Compute the millimoles and weights of magnesium in the antacid sample solution and in the tablet.

1. How many grams O₂
   are needed to react completely with 2.60 mole FeS, in this reaction?      
   4 FeS + 7 O₂→2 FeO₃ + 4 SO₂

   		1.28 x 10 3 g
   		0.258 g
   		329 g
   		44.1 g
   		3.90 x 10 3 g
   		146 g
   		74.7 g
   		1.81 g

2. How many g of Aluminum are needed to react completely with 12.5 mole of Br₂, according to the chemical equation below?
   2Al + 3Br₂→Al₂Br₆
   

   		36.6 g
   		310 g
   		225 g
   		1.42 g
   		145 g

3. How many g of Aluminum are needed to react completely with 0.850 gram of Mn₃O₄, according to the chemical equation below?
   3 Mn₃O₄   + 8 Al --> 9 Mn    +    4 Al₂O₃

   		0.267 g
   		79.2 g
   		20.3 g
   		151 g
   		13.3 g
   		86.5 g
   		14.2 g
   		3.70 g

4. Refer to this equation:
   3SCl₂(l) + 4NaF(s) → SF₄(g) + S₂Cl₂(l) + 4NaCl(s)
   12.0 grams SCl₂ is reacted and 3.05 grams of SF₄ is formed. What is percent yield SF₄?
     
   Hint: find theoretical yield
   Hint: percent yield =(actual yield/ theoretical yield) x 100

   		19.3 %
   		64.4%
   		38.0%
   		27.2 %
   		82.1%
   		72.7%
   		90.1%
   		58.6%

5. Look at the following equation:   
      3H ₂ +   N ₂ ->   2 NH ₃
   
   If 85.0 gram of N ₂ gives 86.2 g of NH ₃, what is the percent yield of
   NH ₃?
   Hint: find theoretical yield
   Hint: percent yield =(actual yield/ theoretical yield) x 100

   		71.7 %
   		69.2 %
   		93.0%
   		45.1%
   		83.5 %
   		36.1%
   		79.2%
   		71.9%

A buffer is prepared by adding 2.78g of potassium acetate to 173mL of 1.25M acetic acid. What is the pH of the buffer? Write the net ionic equation for this buffered solution. (consider pH) How will the pH change if 0.100M HNO3 is added? (Assume volume change is negligible.) How will the pH change if 0.100M KOH is added? (Assume volume change is negligible.) Explain in words what would happen if .200M of HNO3 is added?

1. Explain if the concentration of the base increases, decreases, is not affected or cannot be calculated, for the following situations:

a) the concentration of the HCl solution was less than the actual value

b) when titrating the HCl sample, the tip of the burette contained air bubbles

c) an HCl sample greater than 10.0mL was measured by mistake

d) no indicator was added

e) the container where the HCl was poured was contaminated with acid

. Three moles of an ideal gas (CV,m =3/2R ) is compressed at 25℃, at pressure of 1 atm to 75 atm, with a surrounding maintained at 25℃. The process was performed at condition (i) Reversible and (ii) against constant external pressure of 0.80 atm. Calculate the following q, W, ∆U,∆H, for each path

“Atomic fission” is when a nucleus gets hit by a neutron and splits in half, releasing a great deal of energy. It is the basic principle behind nuclear reactors and nuclear weapons. The “Fat Man” atomic bomb dropped on Nagasaki in 1945 had a plutonium core of 6.4 kg of the isotope Pu-239. (Note that “239” is the molar mass.) When the bomb exploded, it released an amount of energy equivalent to 21 kilotons of TNT.

Although the bomb needed 6.4 kg of plutonium to function at all, only a portion of those plutonium atoms actually fissioned. Calculate how many kilograms of Pu-239 actually underwent fission when the bomb exploded.

You will need some conversion factors to do this problem:

The energy from the explosion of 1 kiloton of TNT is equal to 4.2 x 10¹²J.

The fission of a single atom of Pu-239 releases 210 MeV (mega electron volts) of energy.

1 MeV = 1.602 x 10^-13 J

What is the pH of a 0.15 M solution of potassium nitrite (KNO2)? (The Ka value for nitrous acid (HNO2)

is 4.0x10^-4).

A sample of pure NO2NO2 is heated to 336 ∘C∘C at which temperature it partially dissociates according to the equation
2NO2(g)⇌2NO(g)+O2(g)2NO2(g)⇌2NO(g)+O2(g)
At equilibrium the density of the gas mixture is 0.525 g/Lg/L at 0.755 atm

Calculate Kc for the reaction.

The following data were obtained from experiments to find the molecular formula of an unknown compound which acts as a common local anesthetic. The unknown compound contains only carbon, hydrogen, nitrogen, and oxygen. Complete combustion of a 4.82 g sample of the unknown compound with excess oxygen formed 12.67 g of carbon dioxide and 4.076 g of water. Another sample of the unknown compound with a mass of 1.12 g was found to contain 0.1339 g of nitrogen. The molar mass of the unknown compound was found to be 234 g/mol. Find the molecular formula of the unknown compound.

The laundry bleach is listed at 5.25% m/m NaClO. Calculate the concentration of the NaClO in the laundry bleach solution in mol/L. Assume the density of the bleach solution is of 1.05 g/L.

Consider the following system at equilibrium where K_c = 0.159 and delta H° = -111 kJ/mol at 723 K.

N₂(g) + 3 H₂(g) = 2 NH₃(g)

The production of NH₃(g) is favored by:

Indicate True (T) or False (F) for each of the following:

___TF 1. increasing the temperature.
___TF 2. decreasing the pressure (by changing the volume).
___TF 3. increasing the volume.
___TF 4. adding NH₃.
___TF 5. removing H₂.

Given that Buffer A contains 200 ml of 0.05 M HOCl and 400 ml 0.03 M NaOCl, calculate the pH of the buffer solution, the pH of the solution after adding 10 mL of 0.5 M HCl, and the pH of the solution after adding 20 mL of 0.4 M NaOH.

Given that Buffer B contains 200 mL 0.5 HOCl and 400 mL 0.3 M NAOCl, calculate the pH of the buffer solution, the pH of the solution after adding 10 mL of 0.5 M HCl, and the pH of the solution after adding 20 mL of 0.4 M NaOH.

Which buffer will resist pH changes better?

place the following compounds in order of increasing (weakest to strongest) strength of intermolecular forces
c2h6, ch3oh ch3f

Calculate the pH at the equivalence point for the titration of 0.100 M methylamine (CH3NH2) with 0.100 M HCl. The Kb of methylamine is 5.0