NAME:
______KEY__________
Jan. 31, 2005
QUIZ 2
1) a. Using the data in the table on the right, determine
the number of significant figures that must be reported
before the difference in the mass of 11 H and 11 H+ is
significant. b. What percentage of the mass of a 11 H
atom does the electron represent?
a)
1
1 H = 1.0073 + .0005486 = 1.0078
1 +
1H
b)
Particle
Proton
Neutron
Electron
Mass (AMU)
1.0073
1.0087
5.486x10-4
 need 5 sig figs to tell them apart
= 1.0073
mass of electron
.0005486
X100 =
x100 = 0.00544%
total mass
.0005486 + 1.0073
€
2) How many moles of ammonium ions are in 0.557 g of ammonium carbonate? (show
your work and correct units.) (ammonium = NH4 +, carbonate = CO3 2-) (AW: N = 14.0
g/mol, H = 1.0 g/mol, C = 12.0 g/mol, O = 16.0 g/mol)
2NH 4+ + CO32− → (NH 4 )2 CO3
MW( NH ) CO = (2x14) + (8 x1) + 12 + (3x16) = 96g / mol
4 2
€
3
# mols((NH 4 )2 CO3 ) =
mass(NH 4 )2 CO3 )
9.6g
=
= 0.10mol((NH 4 )2 CO3 )
MW( NH ) CO
96g / mol
4 2
3
€
2mol(NH 4+ )
# mols(NH ) = 0.10mol((NH 4 )2 CO3 )
= 0.20mol(NH 4+ )
1mol((NH 4 )2 CO3 )
+
4
€
€