The unit cell of a ceramic comprised of elements A, B, and C can be described as

Question

The unit cell of a ceramic comprised of elements A, B, and C can be described as a cube with A atoms at the corners of the cube, B atoms in the face-centered positions, and C atoms at the middle of each edge of the cube. The one face of the cell is diagrammed below. The simplest formula for the compound is A_g B_6 C_12 ABC A_4 BC_4 AB_3 C_6 AB_3 C_3 The molecular mass of an organic compound is 190 g/mol and the elemental analysis is 37.87% carbon, 11.68% hydrogen and 50.45% oxygen by mass. The molecular formula of the compound is C_6 H_22 O_6 C_3 H_11 O_3 C_4 H_15 O_2 C_5 H_19 O C_2 H_2 O_4 Which of the substances below CANNOT form hydrogen bonds between molecules in the pure liquid state? (2) only (3) only (1), (3) and (4) (2), (3), and (5) (2) and (3)

Explanation / Answer

26) the atoms at corners contribute 1/8th

Total corners= 8

so total "A" atoms = 8 X 1/8 = 1

The face centered atoms contribute = 1/2

total faces = 6

Total B atoms = 6 X 1/2= 3

Atoms at edge contribute = 1/4th

total edges = 12

So total C atoms = 12 X 1/4 = 3

The formula will be

AB3C3

27) Molecular mass = 190g / mole

the percentage of carbon = 37.87

% of hydrogen = 11.68

% of oxygen = 50.45

Let the mass of compound taken = 100 grams

So mass of carbon =37.87 grams , moles of carbon = mass / atomic weight = 37.87 / 12 = 3.15

Mass of hydrogen = 11.68 , moles of hydrogen = Mass / atomic weight = 11.68 / 1 = 11.68 moles

Mass of oxygen = 50.45 , moles of oxygen = Mass / at wt = 50.45 / 16 = 3.15 moles

Let us divide all the moles by lowest mole number = 3.15

carbon ratio = 3.15 / 3.15 = 1

Hydrogen ratio = 11.68/ 3.15 = 3.7

Oxygen ratio = 3.15 / 3.15 = 1

The empirical formula = CH3.7O   , weight = 12 + 4 + 16 = 32

Molecular weight = 190

Ratio of mol wt and empricial weight = 190 / 31.7 = 5.99 = 6 (approx)

so molecular formula = 6 X emp formula = C6H22O6

28) hydrogen bond is formed between highly electronegative elements (F, O, N) and hydrogen bonded to F, O , N .

1) so in HCOOH there will be hydrogen bond

2) In CH3-OCH3 [an ether] no hdyrogen bond

3) PH3 : no hydrogen bond

4) HF : hydrogen bond will be there

5) CH3COCH3 [ketone] no hydrogen bond

so answer is 2,3 and 5

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