Question

3) Calculate the percentage by mass of hydrogen in PtCl2(NH3)2 A) 0.672 B) 2.016 C) 1.008 D) 0.034 E) 1.558 4) How many molecules of CH4 are in 48.2 g of this compound? A) 1.81 x 1024 B) 4.00 C) 2.00 x 1023 D) 4.64 x 1026 E) 5.00 x 10-24 5) A sample of CH2F2 with a mass of 19 g contains A) 9.5 B) 3.3 * 1024 C) 2.2 x 1023 atoms of F. D) 4.4 x 1023 E) 38 6) How many atoms of nitrogen are in 10 g of NH4NO3? B) 3.0 x 1023 C) 1.8 A) 2 E) 1.5 x 1023 D) 3.5 7) Gaseous neon has a density of 0.900 g/L at standard conditions. How many neon atoms are in 1.00 L of neon gas at standard conditions? A) 1.35 x 1025 B) 5.42 x 1023 C) 6.02 x 1023 D) 7.41 x 10-26 E) 2.69 % 1022 8) How many oxygen atoms are contained in 2.74 g of Al2(SO4)3? A) 6.02 x 1023 B) 12 C) 7.22 x 1024 D) 5.79 x 1022 E) 8.01 x 10-3

Answer 1

3)

Molar mass of PtCl2(NH3)2,

MM = 1*MM(Pt) + 2*MM(Cl) + 2*MM(N) + 6*MM(H)

= 1*195.1 + 2*35.45 + 2*14.01 + 6*1.008

= 300.068 g/mol

Lets calculate the mass of element

mass of H = 6*MM(H)

= 6.048 g

Mass % of H = (6.048*100)/300.068

= 2.016 %

Answer: B

4)

Molar mass of CH4,

MM = 1*MM(C) + 4*MM(H)

= 1*12.01 + 4*1.008

= 16.042 g/mol

mass(CH4)= 48.2 g

use:

number of mol of CH4,

n = mass of CH4/molar mass of CH4

=(48.2 g)/(16.04 g/mol)

= 3.005 mol

use:

number of molecules = number of mol * Avogadro’s number

number of molecules = 3.005 * 6.022*10^23 molecules

number of molecules = 1.81*10^24 molecules

Answer: A

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