26. A 0.397 g sample of a gas occupies a volume of 275 mL at 10°C and 365 torr.

Question

26. A 0.397 g sample of a gas occupies a volume of 275 mL at 10°C and 365 torr. molar mass of the gas ? What is the a) 85.9 g/mol b) 72.8 g/mol )69.8 /mol d) 61.3 g/mol ) 59 27. Choose the name.-formula pair that does not correctly match. a) magnesium phosphate Mgs(PO) b) iron (II) sulfite c) silver carbonate d) potassium fluoride e) copper (II) bromide FeSOs AgCOs KF CuBr 28. How many atoms of hydrogen are there in 88 g of C&Hs;? e)5.3x 102 a) 3.6 x 1023 b) 6.8 x 1022 c) 2.6 x 10 23d)4.1 x 10

Explanation / Answer

Mass of gas m = 0.397 g
volume V = 275 mL = 0.275 L
temperature T = 10 oC = 273 +10 = 283 K
Presssure P = 365 torr = 0.480263 atm
Universal gas constant R = 0.08205 L atm / mol·K

Therefore from ideal gas equation;

PV = nRT
PV = (m/mo..wt)xRT
mol.wt of gas = m.RT/PV
               = 0.397 g x 0.08205 (L atm / mol·K) x 283/0.480263 atm x 0.275L
               = 69.80 g/mol
Hence, the answer is: C (69.8 g/mol)

27) a) magnesium phosphate ---Mg3(PO4)2
this option is correct.
b) Iron(II) sulfite ---FeSO3
This is also correct
c) Silver carbonate ---AgCO3
Silver carbonate is Ag2CO3, hence this is not correct.

d) Potassium fluoride --KF
This is also correct.
e) Copper(II) bromide ---CuBr2
This is also correct.

Therefore, the only option "C" is not correct.
Hence, the answer is: C

28) 88g of C6H6
Molar mass of C6H6 = 78.11 g·mol1
no.of moles of C6H6 = mass/mol.wt
                   = 88 g/78.11 g·mol1
                   = 1.127 mol
Each C6H6 molecule contains 6 atoms of Hydrogen.
therefore, no. moles of Hydrogen = 6 x 1.127 mol
                               = 6.76 mol
No. of hydrogen atoms = 6.76 mol x 6.023 x1023 atom/mol
                      = 40.71 x 1023 atom
                      = 4.07 x 1024 atoms
                      = 4.1 x 1024 atom
Hence, the answer is: d(4.1x1024 )

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