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