Chapter 2 Properties of Matter Chemistry 1

Pure Substances Matter that always has exactly the same composition Every sample the same b/c substance has a fixed, uniform composition 2 categories Element – Ex: Iron (Fe), Copper (Cu), Gold (Au) 2. Compound – Ex: Water, Sugar, Table Salt

Elements Substance that can’t be broken down into a simpler substance Only contains 1 type of atom so has a fixed compositon Atom – smallest particle of an element Room temp (68oF) = most elements are solid Elements: 1 or 2 letters (1st capitalized, 2nd lowercase) Based on Latin names

Compounds Substance made of 2 or more elements in a fixed proportion Can be broken down into simpler substances Compound properties different than elements’ properties that make up compound

Mixtures A mixture is a blend of two or more kinds of matter, each of which retains its own identity and properties. mixed together physically can usually be separated * Homogeneous mixtures are called solutions uniform in composition (salt-water solution) * Heterogeneous mixtures * not uniform throughout (clay-water mixture)

Chapter 1 Classification of Matter

Homogeneous vs. Heterogeneous Not always easy to tell the difference Observe the properties of a mixture Size of the particles in mixture effect the properties Based on the size of its larges particles: solution, suspension, or colloid Solution – homogenous mixture Liquids do not separate into layers over time If poured thru a filter, substances are not trapped Can see thru b/c light passes without being scattered in all directions Very Small particles

Suspensions – heterogeneous mixture “shake well before use” Separate into layers Trapped by a filter Can scatter light in all directions = cloudy Large particles Colloid Contains intermediate particles Do not separate into layers Cannot use a filter to separate Examples: milk and fog *Scattering of light is a property that can be used to distinguish colloids and suspensions from solutions

https://www.youtube.com/watch?v=Vt7lN4QPU0k

Physical Properties 2.2

Physical Properties Characteristic of a material that can be observed or measured without changing composition Viscosity, conductivity, malleability, hardness, melting point, boiling point, density Viscosity its resistance to flow The higher the viscosity, the slower the substance flows Usually decreases when heated Conductivity Ability for heat flow High conductivity = good conductor  metals If good conductor of heat, normally good conductor of electricity

Physical Properties Cont…. Malleability Ability of a solid to be hammered without shattering Most metals are malleable Solids that shatter = brittle Hardness See what materials scratch the other Diamond = hardness known material What do you use to sharpen a knife? Melting/Boiling Point Melting Point – Substance changes from a solid to a liquid Water = 0oC Wax has low melting point Boiling Point – Substance boils Water = 100oC

Density Can be used to test purity d = m/v Test purity of methanol (fuel) d = m/v

Using Physical Properties 2.2 Identifying Material Decide which properties to test Run tests on sample of unknown Compare with previous data reported Choose Materials Wouldn’t want a shoelace from wood (must be flexible and durable)

Using Properties to Separate Mixtures Filtration – process that separates materials based on the size of their particles Small particles can pass thru a strainer Ex: brewing coffee Distillation – process that separates the substance in a solution based (liquid)on their boiling points Ex: fresh water for a submarine Subs can only hold water for about 10 day  convert seawater to fresh water

Recognizing Physical Changes Occurs when some of the properties of a material change but the substance remains the same Ex: phase changes Cutting Crumpling Some can be reversed, some can not

https://www.youtube.com/watch?v=U5lwgmYr36U

Chemical Properties 2.3

Observing Chemical Properties 2.3 Ability to produce a change in the composition of matter Can only be observed when sample is changing to a different substance Ex: Candles Burning Candle = made of paraffin = made of C & H When candle burns, C combines with air to from Carbon Dioxide and H combines with the air to form water.

Chemical Properties Flammability Reactivity Materials ability to burn in the presence of oxygen Ex: paper and gasoline Reactivity How readily a substance combines chemically with other substance Ex: N – extremely low reactivity Ex: O – highly reactive element (rust iron & Oxygen)

Recognizing Chemical Changes Substance reacts and forms one or more new substances Change in Color Jewelry darkens Matches turn black Rust Production of Gas Mix vinegar with baking soda = bubbles of carbon dioxide Baking powder + acid in a cake recipe = bubbles of carbon dioxide Formation of a Precipitate Formation of any solid that separates from a liquid mixture Curdling of milk (lemon juice & milk)

Is a Change Chemical or Physical? Can not be POSITIVE a chemical change has occurred when you see bubbles, color change, or precipitate Ex: water boiling = physical change Iron heated = gray  red = physical change Ask: are different substances present after the change? Chemical Change = Composition of matter changes Physical Change = Composition of matter is the same

Physical vs. Chemical rusting iron chemical dissolving in water Examples: rusting iron dissolving in water burning a log melting ice grinding spices chemical physical

https://www.youtube.com/watch?v=37pir0ej_SE