Density
1 m3 1 liter 1 liter = 1 dm3 1 meter 1 dm3 1 decimeter
1 dm 1 dm 1 liter 1 dm
Imagine that we slice the cube into cm lengths. How many cubes? 1000 cubes We would make smaller cubes the size of a cm. 1 mL = 1cm3 1 mL = 1/1000 L 1 liter 1 dm = 10 cm
1000 = 1 liter
1000 = 1 liter 1 liter 1000 cm3 = 1 liter = 1000 mL 1 cm3 = 1 mL
1 cm3 = 1mL = 1/1000 L It’s important that you know what a cm3 is. And that a cm3 is also equal to a mL. Because density is the mass of 1 cm3 (or 1 mL) of a substance. 1 cm3 = 1mL = 1/1000 L
density = mass/volume density = # of grams/1 cm3 density = x grams/cm3 in grams in cm3 (or mL) density = # of grams/1 cm3 or density = x grams/cm3
Let’s look closer at the cubic centimeter. 1cm3 1cm3 1cm3 substance: water iron nickel mass: 1 gram 8 g 9 g density: 1g/cm3 8 g/cm3 9 g/cm3
substance: water iron nickel density: 1g/cm3 8 g/cm3 9 g/cm3 2g 16g /2cm3 /2cm3 18g /2cm3 3g 24g 27g /3cm3 /3cm3 /3cm3 4g/4cm3 32g/4cm3 36g/4cm3 5g/5cm3 40g/5cm3 45g/5cm3
If you plot the mass versus volume you get a linear graph. 48 If you plot the mass versus volume you get a linear graph. 44 40 36 32 Mass (grams) 28 24 The slope is the density. 20 water iron 16 nickel 12 1 ml,9g 8 1 ml,8g 5 ml,5g 3 ml,3g 4 ml,4g 4 2 ml,2g 1 ml,1g 1 2 3 4 5 6 Volume (mL)
The density of a substance doesn’t change even though you have more of it. When you change the amount of the substance both the mass and volume change. If we had 12 cm3 of water, its mass would be 12 g. density = mass/volume = 12g/12 cm3 = 1g/cm3 still the same density
How can we tell whether the metal is nickel or iron? Sometimes you can identify a metal by its density. For example, suppose we had a chunk of metal and we weren’t sure whether it was iron or nickel. They look the same. How can we tell whether the metal is nickel or iron? density of iron = 8g/mL density of nickel = 9g/ml If we can determine the density of the unknown metal, we can tell whether it’s iron or nickel.
To determine the density we need to know two properties of the metal: its mass _________ __ M density = D = its volume V We would weigh it to get its mass.
If the metal was a rectangular solid, we could figure out its volume by measuring the length, width, and height because . . . V = L x W x H V = 3cm x 2cm x 2cm V = 12cm3 = 12 3cm 2cm 2cm
Chances are though, the metal is not going to be a rectangular solid. How do we determine the volume of this shape?
It’s a method called water displacement. Watch.
The volume of the metal is 12 mL. Water is added to a graduated cylinder. 72 mL 12 mL
iron 96.00 grams density = = 8.0 g/mL or 8.0 g/cm3 12 mL which makes it
Data Table Mass of metal . . . . . . . . . . . . . . . . . . . 96.00 g Volume of water before submersion . . . . 72 mL Volume of water after submersion . . . . 84 mL