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A. What is Chemistry?
Science is the use of evidence to develop testable explanations and predictions of natural phenomena.
• You can use a _______ to take the mass of an object.
• Note: Mass is not the same as ______.
balance
weight
–Weight is mass times the gravitational acceleration, 9.8m/s2.
–Mass will not change if you go to the moon.
A. Properties of Matter
A physical property is a quality or condition of a substance that can be observed or measured without changing the substance.
Example: color, size, shape, density, melting and boiling points
• A chemical property refers to a substance’s ability to undergo a chemical reaction and form new substances. In order to observe a chemical property you must change the substance.
• EX: toxicity, flammability, reactivity
Intensive Properties
An intensive/intrinsic property is one that does not depend on amount.
EX: density, boiling point, melting point
Extensive Properties
An extensive/extrinsic property is one that depends on amount (how much you have).
EX: mass, volume
Practice1. Determine whether the following are
physical or chemical properties:
a) sulfur is yellow
b) sulfur will combine with iron to form iron sulfide.
c) copper is a good conductor of heat.
physical
Chemical
physical
Practice2. Determine whether the following describes
intensive or extensive properties:
a) I have 1 gram of water
b) Water’s freezing point is 0 °C
c) the density of liquid H2O is 1 g/mL
extensive
intensive
intensive
(aq) = aqueous
Aqueous refers to a solid that is dissolved in water
All matter expands when heated and the particles that make up all matter have motion.
Solids• Definite shape
• Definite volume
• No (significant) expansion on heating
• No (significant) compressibility
• Has low energy
• High viscosity
• High density (for most substances)
• Fixed particles
Liquids• Indefinite shape
• Definite volume
• slight expansion on heating
• No (significant) compressibility
• Has moderate energy
• Medium to high viscosity
• Medium density (for most substances)
• Particles slide past each other
Gas• Indefinite shape
• Indefinite volume
• Extensive expansion on heating
• Extensive compressibility
• Has high energy
• low viscosity
• low density
• Fast and continuous motion
Gases are also considered fluid since it flows
Viscosity
• Viscosity is the resistance to flow.
• High viscosity means it flows slower, or the substance is viscous
Ex. Honey has a high viscosity
• You can decrease viscosity by heating up the substance
Density: the ratio of mass to volume
• Formula is: Density = mass/volume• Typical units include:
g/cm3 for solidsg/mL for liquids, and g/L for gases.
But really it is, any unit for mass any unit for volume
Density: the ratio of mass to volume
• Changes when the state of matter changes
• Is an intensive property, therefore doesn’t change when the amount changes
• Less dense objects will float, and dense objects will sink
• Water has a density of 1 g/mL or 1 g/cm3
1. Pure Substances
can be either elements (i.e. Al or H2) or compounds (i.e. H2O, CO2)
Elements are the simplest forms of matter and consist of atoms of all one type (EX: H2, S8, C)
>how do you know if it’s an element?<
An atom is a single unit of an element that retains all the properties of that element.
(ex. Al has 1 atom of Aluminum and S8 has 8
atoms of sulfur)
More on pure substances
• Compounds are two or more atoms chemically bonded together in a set ratio and are shown using a chemical formula. (EX: H2O, C12H22O11 ) The subscript indicates the number of atoms of that element.
Compounds
• substances in a compound lose their individual properties and take on a new set of properties
•Compounds are formed when elements chemically combine and consist of molecules (H2O) or formula units (NaCl)
Molecules & formula units
• A molecule (for molecular compounds) or formula unit (for ionic compounds) is the smallest part of a compound that retains all the properties of the compound
Chemical Separation
• compounds can only be chemically separated, they cannot be physically separated.
Elements can not be physically or chemically separated
Compound
• If you take water, H2O, and add another oxygen to it you now have H2O2, hydrogen peroxide, a completely new substance with complete new properties.
Water Hydrogen peroxide
Oxygen+ =
Compound
• If you take Carbon Dioxide, CO2, and take an oxygen away from it you get Carbon monoxide, CO, a very dangerous and lethal gas.
Carbon dioxide - oxygen = carbon monoxide
Mixtures
• Lemonade… a mixture of water, sugar and lemon juice
• If you add more water you still have lemonade
• If you add more sugar, you still have lemonade
1. Homogeneous Mixtures
• appear to have a uniform composition (look the same throughout)
(disguises itself as a pure substance)
• also known as solutions
• a solution can be any combination of solids, liquids, or gases
• Ex. salt water, brass
Homogeneous Mixture
an alloy is the special term for a solid solution of 2 or more metals. Ex. Brass, sterling silver, stainless steel
2. Heterogeneous mixtures --- do not appear to have a uniform composition
• Includes suspensions and colloids
EX: salads, oil and water, milk
Separating Mixtures
• ChromatographyUsed to separate small
amounts of liquids from each other
Some dyes are more soluble and travel up the paper further
Used to separate a soluble solid out of a liquid
The liquid is heated until it boils once the liquid has boiled off all that remains is the solid
Evaporation
Distillation
Used to collect the liquid from the solid
The liquid is heated and the evaporated liquid is cooled and condensed and collected
Fractional DistillationUsed to separate
liquids from each other
When heated the different liquids evaporate and condense at different temperatures
DissolvingUsed to separate
soluble particles
from insoluble particles
One substance dissolves while the other does not then you filter out the non dissolved particles
practice
1. Determine whether the following are pure substances or mixtures.
a) concrete
b) ice cream
c) NH3
d) potassium fluoride
Mixture
Mixture
Pure Substance
Pure Substance
2. Identify the pure substances below as atoms, molecules, compounds, elements. Two terms may fit.
a) F2
b) Xec) CCl4d) H2SO4
Element / molecule
Element / atom
Compound / molecule
Compound/molecule
3. Identify the following mixtures as homogeneous or heterogeneous.
a) a penny
b) granite countertopc) NaCl(aq)
homogeneous
heterogeneous
homogeneous
More Practice
Pennies(97.5% Zinc, 2.5% Copper)
Category 1Category 2Category 3
SolidMixturehomogeneous
More Practice
Sterling Silver(92.5% pure silver and 7.5% other metals)
Category 1
Category 2
Category 3
SolidMixturehomogeneous
The truth about Gold
18K gold
Category 1Category 2Category 3
SolidMixturehomogeneous
A. Physical vs Chemical• a __________change alters a
substance without changing its chemical composition ; it is reversible. This includes all phase changes.
EX: phase changes, cutting, crushing, dissolving
H2O(s) + heat H2O(l)
ice + heat water
Solid liquid
physical
Boiling vs Evaporation
• There are two types of vaporization: boiling (throughout a liquid) and evaporation (at a surface)
A. Physical vs Chemical
a chemical change occurs when a substance (or substances) changes into new substances; it is not reversible.
EX:rusting, burning, odor forming
Changes in Matter
• Physical Change- alter or change the form or appearance of a substance without changing the material into a new substance
• Chemical Change: A change in matter that creates a new substance with new properties
a) Ice Melts• Changing from
one phase to another is a Physical Change… with water, no matter solid, liquid, or gas, it is still H2O
b) Sugar dissolves in tea
• Sugar in tea can be separated by boiling off the water to leave the sugar behind
d) Nail rusting
• The iron reacts to the Oxygen in the air causing the formation of rust (Ferric Oxide)
e) Silver tarnishing
• Metals such as copper, brass, silver, aluminum reacts with the oxygen in the air and causes it to tarnish
d) Milk Curdling
Chemical!!
The proteins in Milk will hydrolyze, (react with
the water) and eventually come
together and form curds, this is how cheese is made
B. Chemical Reactions
• A chemical reaction occurs when a new substance has been formed
• this is shown typically by a chemical equation
Ex.
Mg + 2HCl H2 + MgCl2--reactants-- ---products---
How to Identify a Chemical Change
• Not all Chemical Changes are easy to see, here are some ways to determine if you have a chemical change.
Formation of a Gas (bubbles)
• Sometimes when two substances come in contact a reaction occurs producing a gas.
Forming of a solid (precipitate)• If you combine
some substances, a reaction can occur forming a solid called a precipitate
Change in Temperature
• When some chemicals react they either give off energy and get hotter (exothermic reaction) or use energy and get cooler (endothermic reaction)
Law of Conservation of Mass
During any chemical change, the total amount of matter remains the same
<Mass can not be created nor destroyed>
Law of Conservation of mass
this means in any chemical reaction, the total mass of the reactants must equal the total mass of the products
reactants products
64 + 192 = 152 + ?
Example: Copper (Cu) and sulfur (S) were heated in a covered container. After the reaction was complete, the unreacted sulfur was removed. The table below contains the results of the investigation. How much sulfur, in grams, was unreacted?
Cu + S CuS + S
1.32 g Sulfur
C. Energy Changes
Heat is a form of energy, and energy is defined as the ability to do work (that is, to exert a force and move something)
Potential Energy
• all substances possess chemical potential energy (the energy stored in atoms and molecules)
during chemical reactions, energy may be released or absorbed. But just as with mass, the total amount of energy of a system before the reaction must equal the total amount of energy of a system after the reaction.
When a reaction gets hotter or colder, this means energy is being transferred from one substance to another. The energy may take on a different form (eg. Light). Remember, energy can not be created or destroyed
• a process that releases energy is ____________
• The surroundings will get warm• The particles slow down
• EX: water ice + heat
exothermic
Endothermic Reactions• a process that absorbs energy is
___________ • The surroundings will get cool• The particles speed up
• EX: ice + heat water
endothermic
Practicea) Steam condensing
Condensing =
gas liquid
Do I need heat? Or do I take heat out of it (cool it down?)
Practiceb) dry ice subliming
Subliming =
Solid gas
Do I need heat? Or do I take heat out of it (cool it down?)