Chem 142
Name ________________________________________
Summer 2011
Section ________________
Worksheet 1: Unit Conversion
1. The volume of an irregularly shaped solid can be determined from the
volume of water it displaces. A graduated cylinder contains 245.0 mL
water. When a small piece of Pyrite, an ore of iron, is submerged in the
water, the volume increases to 315.8 mL. What is the volume of the
piece of Pyrite in cm3 and in liters?
1 mL = 1 cm3 = 0.001 L
V ( mL ) = 315.8mL ! 245.0mL = 70.8mL
(
)
V cm 3 = 70.8mL !
V ( L ) = 70.8mL !
1cm 3
= 70.8cm 3
1mL
1L
= 7.08 ! 10 "2 L
1000mL
2. Dry ice (solid carbon dioxide (CO2)) undergoes sublimation, the process
by which a solid converts to a gas, under standard conditions. A sample
of dry ice weighs 6.54 lbs. After 0.5 hrs, 3.76 lbs of dry ice remains. At
what rate is the dry ice sublimating in kg/min and g/s?
1 kg = 2.21 lbs = 1000 g
rate ( lbs hr ) =
6.54lbs ! 3.76lbs
= 5.56 lbs hr
0.5hr ! 0hr
rate ( kg min ) =
5.56lbs
1kg
1hr
!
!
= 4.2 ! 10 "2 kg min
hr
2.21lbs 60min
4.2 ! 10 "2 kg 1000g 1min
rate ( g s ) =
!
!
= 7.0 ! 10 "1 g s
min
1kg
60s
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Chem 142
Summer 2011
3. A 1.5 mL DNA sample dissolved in water must be frozen before it can
be lyophilized (freeze-dried). The freezer will freeze the sample at a rate
of 0.5 cm3/hr. A bucket of dry ice will freeze the sample as a rate of 0.1
cm3/min. How much time will be saved by freezing the sample in dry ice
vs. the freezer in hours?
t freezer
1hr
1cm 3
=
!
! 1.5mL = 3hrs
0.5cm 3 1mL
t dry ice =
1min
1hr
1cm 3
!
!
! 1.5mL = 0.25hr
0.1cm 3 60 min 1mL
t saved = t freezer ! t dry ice = 3hr ! 0.25hr = 2.75hr
4. A stainless steel ball bearing has a radius of 6.35 mm and a density of
7.75 g/cm3. Iron is the principle element in steel. Carbon is a key minor
element. The ball bearing consists of 0.25% carbon (C), by mass. What
mass of the ball bearing is due to C in g and mg?
1 cm = 10 mm
Vsphere =
4 3
!r
3
3
Vball bearing
4 #
1cm &
3
= ! % 6.35mm "
( = 1.07cm
3 $
10mm '
massball bearing = 1.07cm 3 !
masscarbon ( g ) = 8.31g !
7.75g
= 8.31g
1cm 3
0.25%
= 2.08 ! 10 "2 g
100%
masscarbon ( mg ) = 2.08 ! 10 "2 g !
1000mg
= 20.8mg
1g
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