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Dive into the concepts of matter and energy density, equations, units, and sample problems to grasp density calculations effectively. Explore phases of matter, pure substances, mixtures, compounds, and their distinctions. Discover the significance of density calculations in various scenarios.
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Density • Density: the amount of matter packed into a volume. • Equation: • Units for density include: • g/mL • g/cm3 m d v
cork water brass nut liquid mercury
Sample problems • Find the density of an object in g/cm3 if the mass is 4.370 g and the volume is 2.12 cm3. m = v = D =
A cube of metal has a density of 4.51 g/cm3. If 95.7 grams of the metal is added to 145 mL of water in a graduated cylinder, to what volume would the water rise? m = v = D = Hmm tricky
A cube of metal has a density of 0.997 g/mL and volume of 3019 mL. What is the mass of the cube? m = v = D =
An aluminum block has the mass of 57 grams. The volume of the block .0211 L. What is the density of the aluminum block? What’s the plan? Convert the .0211 L to mL and then solve the problem by dividing 57/21.1
1 2 3 K H D da c m base You move 3 spaces to the right
0.0211 L = 21.1 mL m = v = D =
You enter a pawn shop looking to purchase a gold coin. The shop keeper shows you an amazing looking coin, but you are not sure if it’s 100% gold or not. You purchase the coin for a high price anyway, and test the coin to see if it’s pure gold. Wikipedia says that the density of gold is 19.32 g/cm3.
You bring your coin to chemistry class to conduct an experiment. You fill a large graduated cylinder up to 30.0 mL and carefully drop the coin in. The water rises to 35.6 mL. You place the coin on a balance and find it to be 35.4 grams. What is the density of the gold coin? Should you be happy with your purchase or go back to complain?
m = v = D =
Matter • Matter: anything that takes up space, has mass, and shows inertia. • Inertia: resistance for any object to change its state of motion. Also referred to as Newton’s First Law of Gravity. • The basic piece of matter is the atom.
The atom can be broken down into smaller parts called subatomic particles. • Subatomic particles include: protons, neutrons, and electrons. • Proton: positively (+) charged subatomic particle. • Electron: negatively (-) charged subatomic particle. • Neutron: Neutral charged subatomic particle.
Nucleus: center of atom made of protons and neutrons. • When two or more atoms form a bond, then a molecule is formed.
2. Nucleus 1. Atom Electron Proton Neutron
Water Phosphatidylinositol Methane
Phases and Phase Changes • Three widely known phases: solid, liquid, gas. Important to know what the molecules are like in each phase • Solid: molecules are packed tightly together, but can still vibrate. • Liquid: molecules can move around, but are still close to each other. • Gas: molecules can move around freely, and are not close to each other.
Plasma: state of matter where electrons are stripped from atoms. Occurs at high temperatures. • Ex: florescent light, flame, lightning, sun. Plasma TV’s? Made of millions of tiny “cells” or “florescent lamps.”
Pure Substances • Made up of only one material. • The material can be an element or a compound. • If it is an element, then it’s found on the periodic table. • An element is a pure substance made of only one kind of atom.
Diatomic Gases: gases that are always found in pairs. • Include: H2, N2, O2, F2, Cl2, Br2, I2 • Allotropes: different forms of the same element. • Example: diamonds and graphite.
Compounds: form when two different elements join chemically. • When a chemical reaction occurs, both physical and chemical properties are highly likely to change.
Mixtures: homogeneous and heterogeneous mixtures • A mixture is a physical combination of two substances. • The different parts can be separated physically using various methods. • No new substances should be occurring.
Heterogeneous mixture: a mixture that is not equally mixed. • Different regions have different physical properties. • Ex: Italian dressing, pepperoni pizza, chocolate chip cookies.
Homogeneous mixture: mixture that has particles evenly mixed. • All phases of matter (solid, liquid, and gas) can be in a homogeneous mixture. • Ex: air, gasoline, 14-karat gold • Homogeneous metals are called alloys. • Homogeneous liquids are called solutions. • Solutions cannot be separated through a filter.
Carat measures two things: mass and purity. Carats for rings are based on 24-carat scale. 24 carat is pure gold. 14 carat-gold rings would have slightly more than half gold. 10 carat rings would be slightly less than half gold.
Brass is not a pure metal. It’s a homogeneous mixture of copper and zinc.
Mixtures Vs. Compounds • Mixtures are physical combinations. Compounds are chemical combinations. • Compounds change properties, while mixtures have a combined property. Ex: Alloys are normally stronger (Steel made of iron and carbon). Methanethiol (mercaptan) gas added to natural gas. Methanethiol still smells.
Atoms in compounds always combine in whole numbers. No fractions or decimals. • Ex: H2O. CO2. You never see H3.5O or CO9.2 • To separate a compound back into its pure substances, then you must use other chemical reactions. • Mixtures can be separated using physical methods.
Physical Vs. Chemical Property • Chemists - and you - will study physical and chemical properties. In order to study both you must be able to determine the difference. • Physical property: observations made without changing the composition or identity of a substance.
H2O • Ex: ice is made of what molecule? _______ • Ice will melt at what temp? ___________ • What is the molecule after when ice melts to water? _____________ Think of your own example of a physical property. 0ºC or 32ºF H2O
Physical properties can be categorized as either extensive or intensive. • Extensive physical properties: a property where the amount of matter is important. • Example: mass, volume, length, and size. • Intensive physical properties: a property where the amount of matter is not important. • Example: color, density, melting point, boiling point.
