Calculate the Mass of 8

KEY 26 1.Calculate the mass of 8.43 x 10 atoms of silver.

Mass = (# atoms / N) x atomic mass 26 23 5 Mass = (8.43 x 10 atoms / 6.022 x 10 atoms/mol) x 107.9 g/mol = 1.51 x 10 g

2.What is the mass of 1.48 mol of potassium sulfide, K2S?

Mass = mol x molar mass

Molar mass K2S = 2(39.0) + 32.1 = 110.1 g/mol Mass = 1.48 mol x 110.1 g/mol = 163 g

3.Calculate the molar mass of barium nitrate, Ba(NO3)2.

Element # atoms atomic mass Ba 1 x 137.3 = 137.3 N 2 x 14.0 = 28.0 O 6 x 16.0 = 96.0 241.3 g/mol

4.What is the molar mass of nitroglycerin, C3H5(NO3)3?

Element # atoms atomic mass C 3 x 12.0 = 36.0 H 5 x 1.0 = 5.0 N 3 x 14.0 = 42.0 O 9 x 16.0 = 144.0 227.0 g/mol

5.What is the molar mass of Al(OH)3?

Element # atoms atomic mass Al 1 x 27.0 = 27.0 O 3 x 16.0 = 48.0 H 3 x 1.0 = 3.0 78.0 g/mol

6.What is the molar mass of C12H22O11?

Element # atoms atomic mass C 12 x 12.0 = 144.0 H 22 x 1.0 = 22.0 O 11 x 16.0 = 176.0 342.0 g/mol 7.Calculate the number of ammonia molecules in 25.0 g of ammonia, NH3.

# molecules = (mass / molar mass) x N

molar mass NH3 = 14.0 + 3(1.0) = 17.0 g/mol # molecules = (25.0g / 17.0 g/mol) x 6.022 x 1023 molecules/mol = 8.86 x 1023 molecules

8.Convert: 17.8 g CO2 = ______molecules CO2

molar mass CO2 = 12.0 + 2(16.0) = 44.0 g/mol # molecules = (17.8g / 44.0 g/mol) x 6.022 x 1023 molecules/mol = 2.44 x 1023 molecules

9.Convert: 0.546 mol AgNO3 = ______g AgNO3

Mass = mol x molar mass

Molar mass AgNO3 = 107.9 + 14.0 + 3(16.0) = 169.9 g/mol Mass = 0.546 mol x 169.9 g/mol = 92.8 g

10.Convert: 2.56 mol N2O = ______molecules N2O

# molecules = mol x N # molecules = 2.56 mol x 6.022 x 1023 molecules/mol = 1.54 x 1024 molecules

11.Convert: 0.21 mol KCl = ______g KCl

Mass = mol x molar mass Molar mass KCl = 39.1 + 35.5 = 74.6 g/mol Mass = 0.21 mol x 74.6 g/mol = 15.7 g

12.Convert: 10.23 g NaBr = ______molecules NaBr

# molecules = (mass / molar mass) x N molar mass NaBr = 23.0 + 79.9 = 102.9 g/mol # molecules = (10.23g / 102.9 g/mol) x 6.022 x 1023 molecules/mol = 5.99 x 1022 molecules

13.A 14.2-g sample of Ba(NO3)2 contains how many molecules of Ba(NO3)2?

molar mass Ba(NO3)2 = 241.3 g/mol (see problem 3 above) # molecules = (14.2g / 241.3 g/mol) x 6.022 x 1023 molecules/mol = 3.54 x 1023 molecules

14.A 50.0-g sample of H2O contains how many molecules of water?

molar mass H2O = 2(1.0) + 16.0 = 18.0 g/mol # molecules = (50.0g / 18.0 g/mol) x 6.022 x 1023 molecules/mol = 1.67 x 1024 molecules