Measurements

1
Measurements

• Conversion Factors and Problem Solving
• Density and Problem Solving

2
Conversion Factors

• Equalities can be used to create conversion
  factors
  
• Example 1 m 100 cm
• Factors 1 m and 100 cm
• 100 cm 1 m
• We will focus only on metric-metric, measured
  number-exact number and percent conversion
  factors.
  
• Examples 100 cm/m, 10.0 mg/1 tablet, 20
  0.200
  

3
Solving Generic Problems Using Conversion Factors

• Identify or summarize all the numerical data
  including equalities and their unit labels
  
• Identify the answer and it units
• Develop a conversion plan to change one unit into
  another.
  
• Combine (usually multiply) the conversion factors
  so each unit NOT in the final answer cancels
  out.
  

4
Solving Generic Problems Using Conversion Factors

• Example
• Dr. Alverez orders 0.050 g of a medication for a
  patient. If each tablet contains 10. Mg of
  medication, how many tablets are needed?
  

5
Density

• Which weighs more a kilogram of rocks or
  feathers?
  
• Which weigh more a liter of rocks or feathers?
• Will rocks or feathers float on water? Why?

6
Learning Check

• Which diagram represents the liquid layers in
  the cylinder?
  
• (K) Karo syrup (1.4 g/mL), (V) vegetable oil
  (0.91 g/mL,) (W) water (1.0 g/mL)
  
• 1) 2) 3)

K
W
V
V
K
W
W
V
K
7
Density

• Density compares the mass of an object to its
  volume
  
• Density mass g or g
  
  
• volume mL
  cm3
  
• Note 1 mL 1 cm3
• Specific gravity density of sample
• density of water (1 g/mL)

8
Volume Displacement

• A solid displaces a matching volume of water
  when the solid is placed in water.
  
• 33 mL
• 25 mL

9
Learning Check

• What is the density (g/cm3) of 48 g of a metal
  if the metal raises the level of water in a
  graduated cylinder from 25 mL to 33 mL?
  
• 1) 0.2 g/ cm3 2) 6 g/m3 3) 252
  g/cm3
  
• 33 mL
• 25 mL

10
Solving Generic Problems Using the Mathematical
Formula Method

• Identify the math formula that includes the the
  given data and the unknown.
  
• Identify the unknown then assign numbers to each
  known quantity.
  
• Substitute the known values in the math
  equation.
  
• Algebraically transform the equation so that the
  unknown is alone on one side.
  
• Calculate the final answer, check the answers
  validity and the number of SF.

11
Solving Generic Problems Using the Mathematical
Formula Method

• Example
• A thermometer contains 8.3 g of mercury. What
  volume of mercury is percent? The density of
  mercury is 13.6 g/mL