Pure Substances vs. Mixtures Physical and Chemical Changes

Anything that has mass and takes up space is called matter.

There are 2 types of matter: Pure Substances Mixtures

Matter that has a fixed composition (Has a chemical formula) and definite properties. (chemical and physical)

Elements Compounds There are two kinds of pure substances

Pure substances are CHEMICALLY combined- what does that mean?

Element Substance that cannot be separated or broken down into simpler substances by normal means. Made of only 1 type of atom Ex’s- any box on the periodic table Remember atoms are defined by their number of ____________ Protons!

Elements can be atoms or molecules ATOMS: Only one atom MOLECULE: Two atoms (can be of the same element) bonded together

Compounds cont… Substance made of atoms of 2 or more different elements that are CHEMICALLY combined. This means they are BONDED at the electrons! Has a chemical formula- ex ______________

When elements combine, it is in a definite way and this changes their properties Na- lethal if ingested Cl- lethal if ingested NaCl- table salt

Molecules vs Compounds Molecules are two or more atoms bonded together…but compounds must have two different elements Ex- O2, NaCl, etc. REMEMBER: Not all molecules are compounds, but all compounds are molecules…explain

Compounds Molecules made by two or more elements bonded together -always in a definite ratio Elements Molecules made of just one element Na (sodium) NaCl (sodium chloride/salt)

Cannot be separated into simpler substances by physical methods (physical changes) Atoms are bonded together in a fixed composition Properties do not vary Can be expressed with a chemical formula Ex H2O, NaCl, H

Two or more substances that are physically combined. (NOT chemically combined/bonded like a pure substance) Can be separated into pure substances by physical processes Ex- Salt water can be separated into 2 pure sustances: __________ and _____________. May have similar properties to the substances that make it (ex- sugar water)

Examples of Mixtures

Components retain their characteristic properties and can be separated by physical means. suspensions-video.htm suspensions-video.htm This sand and iron filings mixture can be separated using a magnet.

Two types of mixtures

Homogenous mixtures look the same throughout Types: solutions, alloys, etc. Example: salt water, brass

Have the same composition throughout Components are indistinguishable Will not scatter light Particle size is small

Can they still be separated by physical means ? YES!!! It may be more complicated, but it can be done…distillation, centrifugation

Solutions are … homogenous mixtures that do not scatter light. separated by physical means (including distillation or evaporation.) created when something is completely dissolved in pure water. Examples: sugar water, salt water

Parts of a Solution Solute- substance that dissolves in solvent ex. Salt (“U dissolve”) Solvent- substance that does the dissolving (ex.water) Well, not really, because you don’t dissolve, but you get the picture

Why don’t you dissolve? You are not “Miscible” Miscible- two or more liquids that can dissolve into each other (aka- soluble) Immiscible- liquids that do NOT mix (aka- insoluble) Ex- oil and water

Heterogeneous mixtures are composed of medium or large pieces that are easily separated by physical means (ie. density, polarity, metallic properties).

Do not have same composition throughout Usually components are distinguishable Particle size is medium or large Examples: fruit salad, vegetable soup, etc.

Tyndall Effect Scattering of light due to particles

1. Colloid –medium particles Particles stay suspended in the mixture and scatter light (Tyndall effect) Ex- mayonnaise, milk, fog

1. Suspension- large particles Tyndall effect Particles will settle out when the mixture is allowed to stand Ex-muddy water, OJ with pulp

Properties of Matter

Physical properties are those that we can determine without changing the identity of the substance. Properties we can observe or measure

color Melting/boiling point

Viscosity Resistance to flowing Maple Syrup- High Viscosity Water- Low Viscosity

Ductility Ability to be drawn into a thin wire

Malleability Ability to be hammered into thin sheets without shattering

Hardness Resistance to being scratched

Conductivity Ability to carry electricity High Conductivity (the liquid is able to let electrons flow to complete the circuit Low Conductivity (the liquid is NOT able to let electrons flow to complete the circuit

Solubility Ability to dissolve in water Yes! It is a physical property because you do not need to alter identity of the substance to determine solubility.

DENSITY Mass per unit volume Calculated by: Density= Mass/Volume D=M/V Units: g/mL g/cm 3

Density determines if an object will sink or float in water. - if an object is LESS dense it will FLOAT - If it is MORE dense it will SINK

Density Tower

Density Graphs Y axis= X axis= Slope=

Other examples of physical properties….

Chemical Properties Describe the way a substance can change or react to form other substances. (what bonds they will form) (NOT the actual reaction- that’s a chemical change) Must be determined using a process that changes the identity of the substance (chemical reactions involve breaking and making new bonds)

One of the chemical properties of alkali metals such as sodium and potassium is that they react with water. To determine this, we would have to combine an alkali metal with water and observe what happens. In other words, we have to define chemical properties of a substance by the chemical changes it undergoes.

Ex’s of Chemical Properties Reactivity: ability of a substance to combine CHEMICALLY (at the electrons) with another substance (to form a compound)

Flammability Ability of a material to burn in the presence of Oxygen.

Alkalinity Ability to neutralize acids

A change that does not change the chemical composition of a substance. Ex: changes in size, shape, appearance, etc. Why? The form or appearance has changed, but the properties of that substance are the same (i.e. it has the same melting point, boiling point, chemical composition, etc.)

A chemical change occurs when a substance changes into something new (breaking & reforming new bonds. This occurs due to heating, chemical reaction, etc. You can tell a chemical change has occurred if the density, melting point or freezing point of the original substance changes. Many common signs of a chemical change can be seen (bubbles forming, mass changed, etc).

Recall: A chemical change occurs when a substance changes into something new. Foaming Bubbles New odor Heat production or drop in temperature New precipitate (solid formed from liquids)