Taking Mass and Volume Measurements with Accuracy & Precision.
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Transcript of Taking Mass and Volume Measurements with Accuracy & Precision.
Taking Mass and Volume Measurements with Accuracy & Precision
What is a measurement?
Measurement is the process of determining a physical quantity such as length, time, temperature, etc.
Accuracy & Precision
Accuracy: how close a measured value is to the actual (true) value.
For example: The actual density of gold is 19.32 g/cm3. If you measure the density of gold and your value is fairly close to 19.32 g/cm3, then you took an accurate measurement.
Accuracy & Precision
Precision is consistently getting the same measurement even if it is not right.
Accuracy vs. Precision
Low Accuracy High Accuracy High AccuracyHigh Precision Low Precision High Precision
Why Does This Matter?It is important to take accurate and precision
measurements because we will be using many chemicals this term like: CaO2, AgNO3, NaOH, HCl, H2O2,, and more.
Mixing too much of a substance can potentially create a violent reaction.
http://www.youtube.com/watch?v=ODf_sPexS2Q&feature=
related
http://www.youtube.com/watch?v=MTcgo46nxNE&feature=
fvwrel
Today’s Measuring Focus:
Mass
Volume
Density
What is Mass
Mass is the amount of matter in a substance… it is NOT weight.
However, you can find an object’s weight by multiplying its mass by the acceleration of gravity which is…
9.8 m/s2
Mass is measured with a…
Triple Beam Balance or…
Electronic Scale
Units for Mass
The triple beam balance gives mass in grams (g)
But there are many other units for mass like:Kilograms (kg)Milligrams (mg)
1 kg = 1000 g 1 g = 1000 mg
Total Mass = 373.4 g ….or 0.3734 kg
70 g300 g
3.4 g
Your Turn
Find the mass of the object given to you
What is Volume?
Volume the amount of space taken up by an object or substance.
Volume can be measured with…
RulerGraduted Cylinder or …
Units for Volume
Liters (L)
Milliliters (mL) or
Centimeters cubed (cm3)
1 L = 1000 mL
1 mL = 1 cm3
Measuring volume of a regular shaped object
….Like a cube
Volume = 5x5x5 = 125 cm3
Your Turn!
Find the volume of your cube and record it on your handout
Measuring volume of a liquid
Volume should be read from the
Meniscus of a graduated cylinder
Measuring volume of an irregularly shaped
object…like a fish
1. Find initial volume
2. Put object in
3. Find final volume
4. Subtract two values
Volume of water = 32 mL
Volume of water + fish = 38 mL
Volume of fish:
38mL – 32mL = 6 mL
Your Turn!
Find the volume of your marble
What is Density?
Density is the measure of how tightly compact the matter in a substance is.
Density = mass/volume
Example
Which do you think is more
dense: a Styrofoam ball or
a marble?
Marble
Marble:
Mass = 8.1 g
Volume = 2.5mL
Density = 8.1g/2.5mL = 3.24 g/mL
D = m/V
Styrofoam:
Mass = 4.8 g
Volume = 30 mL
Density = 4.8g/30mL =0.16 g/mL
D = m/V
Find the Density of a Penny
1.Find the mass of a group of pennies
2.Find the volume using a graduated cylinder
3.Divide the mass by the volume
DENSITY OF WATER
Dwater = 1.00 g/mL
ALWAYS!
Units for Density
g/cm3
g/mL
kg/m3
Independent Practice:You may work with a partner
Tips for working in a group1. Read the question to yourself
first2. Try to find the answer on your
own3. Compare it to your partner’s4. Discuss any differences in your
answers