Matter: anything that occupies spaced and has mass Matter can be distinguished by its physical properties Physical property: a property that can be observed/or measured without changing the chemical makeup of the substance What are some physical properties? color melting and boiling point odor
Density: the mass of a material within a given volume - The density of liquid water is usually given as 1 g/mL, but it’s actually temperature dependent
- 1 cm3 = 1 mL (this is super useful for the rest of the year so MEMORIZE it now!)
Freezing point: the temperature at which a substance changes from a liquid to a solid - For water, it is of course, 0°C
What others can you think of?
Graphite — layer structure of carbon atoms reflects physical properties. Graphite — layer structure of carbon atoms reflects physical properties. This allows layers to easily be removed. This easy transfer of layers is why we use it in pencils!
Water is the only ordinary liquid found in naturally in our environment - Because so many substances dissolve readily in water, quite a few liquids are actually water solutions
- A water-based solution is an aqueous solution
BTW, what’s a chemical property? A property that can only be observed and/or measured if the substance is chemically altered (Example: flammability)
- can be observed without changing the identity of the substance
Some physical changes would be boiling of a liquid melting of a solid dissolving a solid in a liquid to give a homogeneous mixture — a SOLUTION.
Chemical change or chemical reaction — transformation of one or more atoms or molecules into one or more different molecules. Chemical change or chemical reaction — transformation of one or more atoms or molecules into one or more different molecules.
Heat Heat Odor change Gas Produced (not from boiling!) Precipitate – a solid formed by mixing two liquids together Color change
Examples: Examples: - melting point
- flammable
- density
- magnetic
- tarnishes in air
Examples: Examples: - rusting iron
- dissolving in water
- burning a log
- melting ice
- grinding spices
BUT, physical properties & changes are important, too! BUT, physical properties & changes are important, too! ALL mixtures can be separated physically. They can be separated based on their PHYSICAL properties.
Problem A piece of copper has a mass of 57.54 g. It is 9.36 cm long, 7.23 cm wide, and 0.95 mm thick. Calculate density (g/cm3). Problem A piece of copper has a mass of 57.54 g. It is 9.36 cm long, 7.23 cm wide, and 0.95 mm thick. Calculate density (g/cm3).
Strategy Strategy 1. Get dimensions in common units. 2. Calculate volume in cubic centimeters. 3. Calculate the density.
SOLUTION SOLUTION 1. Get ALL dimensions in common units. 2. Calculate volume in cubic centimeters. 3. Calculate the density.
Strategy Strategy 1. Use density to calc. mass (g) from volume. 2. Convert mass (g) to mass (lb) = 454 g / 1 lb
1. Convert volume to mass 1. Convert volume to mass
Osmium is a very dense metal. What is its Osmium is a very dense metal. What is its density in g/cm3 if 50.00 g of the metal occupies a volume of 2.22cm3? 1) 2.25 g/cm3 2) 22.5 g/cm3 3) 111 g/cm3
2) Placing the mass and volume of the osmium metal into the density setup, we obtain D = mass = 50.00 g = volume 2.22 cm3 = 22.522522 g/cm3 = 22.5 g/cm3
A solid displaces a matching volume of water when the solid is placed in water. A solid displaces a matching volume of water when the solid is placed in water. 33 mL 25 mL
Density is an INTENSIVE property of matter. Density is an INTENSIVE property of matter. - does NOT depend on quantity of matter.
- Temperature is also intensive
Contrast with EXTENSIVE
Most density tables are given with a specific temperature because substances expand when heated. Most density tables are given with a specific temperature because substances expand when heated.
Directly proportional – the relationship between two variables can be expressed as y/x = k where k is a constant. Directly proportional – the relationship between two variables can be expressed as y/x = k where k is a constant. Graphs of directly proportional variables are linear.
If mass is your y variable, and volume is your x variable, y/x = k! (m/V = D) If mass is your y variable, and volume is your x variable, y/x = k! (m/V = D)
In inversely proportional relationships, yx = k This type of graph is curved. We will see this a lot more when we get to the gas laws later in the year.
1) What is a physical property? 1) What is a physical property? 2) Identify three physical properties of water. 3) How does the density of solid water compare to the density of liquid water? 4) Describe a setting where you might observe water as a solid, a liquid, and a gas all at the same time. 5) Distinguish between physical changes and chemical changes. 6) A star is estimated to have a mass of 2 x 1036 kg. Assuming it to be a sphere of average radius 7.0 x 105 km, calculate the average density of the star in units of grams per cubic centimeter. CONTINUED…
7) Classify the following as physical or chemical changes. 7) Classify the following as physical or chemical changes. - a) Moth balls gradually vaporize in a closet.
- b) Hydrofluoric acid attacks glass, and is used to etch calibration marks on glass laboratory utensils.
- c) A French chef making a sauce with brandy is able to burn off the alcohol from the brandy, leaving just the brandy flavoring.
- d) Chemistry majors sometimes get holes in the cotton jeans they wear to lab because of acid spills.
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