calculate The lattice enthalpy (in kJ/mol) for calcium fluoride is: Which of the

Question

calculate The lattice enthalpy (in kJ/mol) for calcium fluoride is: Which of the following changes will NOT affect the total pressure of gas in a container, assuming all other factors remain constant? Tetraphosphorus hexaoxide (MM = 219.9 g/mol) is formed by the reaction of phosphorus with oxygen gas. P_i(s) + 3O_2 (g) rightarrow P O (s) If a mixture of 75.3 g of phosphorus and 38.7 g of oxygen produce 43.3 g of P_4O_6, what is the percent yield for the reaction? A 0.100 m MgSO_4 solution has a freezing point of -0.2.3 degree C. What is the van't Hoff factor for this solution? K_f = 1.86 degree C/m Which of the following should have the lowest boiling point? The pH of 0.15 M NH_2 OH(aq) is 9.60. What is the percent of NH_2 OH protonated ?

Explanation / Answer

Solution :-

Q20) The lattice energy of the CaF2 is   - 2617 kJ per mol

Q21) the total pressure will not change when the half of the moles of gas is replaced by the moles of other gas with different molar mass

Because the overall molecules in the container remains the same

So the anaswer is the option D

Q22)

Lets calculate the theoretical yield of the P4O6 using the mole ratio of the reactant and products

(75.3 g P4 * 1 mol / 123.89 g )*(1 mol P4O6/1mol P4)*(219.88 g / 1 mol P4O6) = 133.6 g P4O6

(38.7 g O2*1mol / 32 g)*(1 mol P4O6/ 3mol O2) *(219.88 g / 1 mol P4O6) = 88.6 g P4O6

Since the O2 gives the less mass of the product therefore therefore tical yield = 88.6 g P4O6

Now lets calculate the percent yield

% yield = (actual mass / theroretical mass)*100%

             = (43.3 g / 88.6 g) *100%

             = 48.8 %

So the correct answer is option b

Q23 )

Change in the freezing point delta Tb = 0 C – (-0.23 C) = 0.23 C

Kf water = 1.86 C /m

0.100 m MgSO4

Vant hoff factor i = ?

Delta Tf = Kf* m * i

Delta Tf / Kf * m = i

0.23 C / 1.86 C per m * 0.100 m = i

1.2 = i

So the vant hoff factor for the MgSO4 is 1.2

So the answer is option C

Q24)

Boiling point increases with the increase in the moalr mass therefore the formula C5H12 that is option A has lowest number of carbons means lowest molar mass so the boiling point of the C5H12 will be lowest.

So answer is option A

Q25 )

pH= 9.60

lets calculate the pOH

pOH = 14 – pH

pOH = 14 – 9.60 = 4.4

now using the pOH lets calculate the OH-

pOH = -log [OH-]

[OH-] = antilog [ - pOH]

        = antilog [-4.4]

       = 3.98*10^-5 M

Now lets calculate the percent ionization

% ionization = ([x]/[NH2OH]) * 100 %

                      =(3.98*10^-5 / 0.15) *100 %

                     = 0.027 %

So the correct answer is option A

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