Transcript Problem Solving in Chemistry

Problem Solving in
Chemistry
Dimensional Analysis
a way to analyze and solve problems
using units or dimensions of
measurements
Problem Solving in
Chemistry
Examples
- What is the mass, in grams, of a piece of lead that has
a volume of 19.84 cm3 and a density of 11.4 g/cm3 ?
Known:
Volume of lead= 19.84 cm3
D = 11.4 g/cm3
Unknown:
Mass = g
m = 226 g
Make sure you
Calculate:
include units with
D = m/v
everything!
Problem Solving in
Chemistry
A small piece of gold has a volume of 1.35 cm3;
the density of gold is 19.3 g/cm3. What is the
value of this piece if the market value of gold is
$11/g?
Known:
Volume of gold= 1.35 cm3
D = 19.3 g/cm3
$290
Unknown:
Don’t round
Mass = g
until you are
Calculate:
finished!
D = m/v
Conversion Factors
•0.044 km to meters
•4.6 mg to grams
•8.9 m to decimeters
•0.107 g to centigrams
44 m
4.6x10-3 g
89 dm
10.7 cg
Problem Solving in
Chemistry
The directions for an experiment ask each
student to measure out 1.84 g of copper
(Cu) wire. The only copper wire available
is a spool with a mass of 50.0 g. How
many students can do the experiment
before the copper runs out?
27 students
Problem Solving in
Chemistry
The radius of a potassium atom is 0.227 nm.
Express this radius in centimeters.
2.27 x10-8 cm
How many seconds are there in one day?
8.64 x104 s
Problem Solving in
Chemistry
A flask that can hold 158 g of water at 4°C
can hold only 127 g of ethanol. What is the
density of ethanol?
0.804 g/mL
How many kilograms of water are needed to
fill an aquarium that measures 40.0cm by
20.0cm by 30.0cm?
24 kg
Problem Solving in
Chemistry
A watch loses 0.15 s every minute. How
many minutes will the watch lose in 1 day?
2.0 x10-6 min
- A cheetah can run 112 km/h over a 100-m
distance. What is this speed in meters per
second?
31.1m/s