HW = Study for Monday’s Ch 8 Exam

a) 1.0 mol zincb) 1.0 mol copperc) 1.0 mol potassiumd) 1.0 mol sulfure) all have the same mass

Which of the following has the greatest mass?

How many mol of CO2 are in 3.3 g of carbon dioxide?

(a) 145.233 mol (b) 0.075 mol (c) 150 mol (d) 13 mol (e) none of the above

3.3 g CO2 ( ) 1 mol CO2= 0.075 mol CO2 44.01 g CO2

MOLE(mol)

Mass(g)

Particles(atoms or

molecules)

MOLAR

MASSAVOGADRO’SNUMBER

How many mol of CO2 are in 3.3 g of carbon dioxide?

How many grams of uranium are in 5.00 X 1022 atoms of pure uranium?

(a) 19.8 g (b) 0.0830 g (c) 0.000349 g(d) 1.19 x 1025 g (e) none of the above

5.00 x 10 22 atoms U ( )6.022 x 1023 atoms U 1 mol U ( ) 1 mol U

238.00g U

= 19.8 g U

MOLE(mol)

Mass(g)

Particles(atoms or

molecules)

MOLAR

MASSAVOGADRO’SNUMBER

How many grams of uranium are in 5.00 X 1022 atoms of pure uranium?

In order to determine the molecular formula of a compound you only need to know its empirical formula?

a) Trueb) False

HF5 H2F10???

Find n = molar mass = 192.92g/mol empirical mass 95.96 g/mol

n = 2

To find molecular formula… A. Find empirical formula.

B. Find empirical mass

C. Find n = molar mass empirical massD. Multiply all parts of empirical formula by n

A compound having an approximate molar mass of 165-170g/mol has the following percent composition by mass. Determine its molecular formula.

42.87% C3.598% H28.55 % O25.00% N

a) C2H2ONb) C4H4O2N2

c) C6H6O3N3

d) CHONe) none of the above

= 3.57 mol C

= 3.56 mol H

= 1.78 mol O

/ 1.78 mol

/ 1.78 mol

/ 1.78 mol

= 2 C

= 2 H

= 1 O

42.87% C

3.598% H

28.55% O

42.87g C

3.598g H

28.55g O

C g 12.01

C mol 1

1 mol H

1.01 g H

1 mol O

16.00 g O

Step 1) % g Step 2) g mol Step 3) mol mol

Step 4) return to whole

X

X

X

= 1.78 mol N = 1 N

N g 14.01

N mol 1 / 1.78 mol25.00% N 25.00g N

C2H2ON

n = molar mass empirical mass

= 167g mol = 2.98 56.05 g/mol

C6H6O3N3

Determine the percent composition of sulfuric acid.

a) 28.57% H, 14.29 % S, 57.14% Ob) 2.055% H, 32.70 % S, 65.25% Oc) 1.02% H, 32.70 % S, 16.31% Od) none of the above

Determine the percent composition of sulfuric acid.

MOLAR MASS of H2SO4 = 98.09 g/mol% H = mass H = 2.02 g . = 0.02055

molar mass 98.09 g

2.055% H, 32.70 % S, 65.25% O

% S = mass S = 32.07 g . = 0.3270 molar mass 98.09 g

% H = mass O = 64.00 g . = 0.6525 molar mass 98.09 g

Percent Abundance Practice – Part I

Silicon has three naturally ocurring stable isotopes, silicon-28, silicon-29 and silicon-30 with respective percent abundances of 92.23%, 4.69% and 3.08%. What is the average atomic mass of silcon?

Weighted Average = Value A (%A) + Value B (% B) + Value C (% C) + …

28amu (.9223) + 29amu (.0469) + 30 amu (.0308) = 28.11 amu

Percent Abundance Practice – Part IIGallium has an average atomic mass of 69.79 amu and its stable isotopes are 71Ga and 69Ga. Find the percent abundances of gallium’s isotopes.

Molar Mass Ga = 69.79 g/mol

71Ga

69Ga

Difference between average and each isotope = 1.21 amu and 0.79 amu

Difference in mass between

71Ga and 69Ga = 2.00 amu

0.79 amu2.00 amu

x 100 = 39.5 %

1.21 amu2.00 amu

x 100 = 60.5 %