Identifying Unknowns
Testing for Identification Although non-characteristic properties can be shared by many different substances, they can still be useful in helping to identify an unknown Substances will have different combinations of noncharacteristic properties Some non-characteristic properties can be used to determine a characteristic one (volume & mass are used to calculate density)
Testing for Identification The following are some of the tests that you will be doing in order to identify unknown substances this year! Electrical conductivity Magnetism Presence of water ph level Presence of glucose Presence of protein Presence of fat Presence of hydrogen gas Presence of oxygen gas Presence of carbon dioxide gas Metallic lustre Malleability Mass Volume Colour
Electrical Conductivity How: Conductivity meter Possible outcomes: Light turns on = Substance conducts! Keep in mind that some substances are better conductors than others
Presence of Water (H 2 O) How: Cobalt chloride paper Possible outcomes: Turns light pink = There s water present in the solution! Stays blue = No water present
Acid, Base or Neutral How: Red and blue litmus paper Possible outcomes: Red Red, Blue Blue = neutral Red Blue, Blue Blue = base Red Red, Blue Red = acid
Presence of Glucose How: Glucose test paper Possible outcomes: Stays yellow = No glucose Turns green = Glucose is present in the solution
Presence of Protein How: Biuret solution (protein test solution) Possible outcomes: Turns blue = No protein Turns purple = Protein is present in the solution
Protein or no protein? Protein No protein Protein
Presence of Fat How: Alcohol test Possible outcomes: Stays transparent = No fat Turns white and cloudy = Fat is present in the solution
Presence of Hydrogen Gas How: Lit splint test Possible outcomes: A popping sound = Hydrogen gas is present
Presence of Oxygen Gas How: Glowing splint test Possible outcomes: The splint reignites = Oxygen gas is present The splint extinguishes = No oxygen gas is present
Presence of Carbon Dioxide Gas How: Limewater (CaOH 2 ) test Possible outcomes: Limewater stays transparent and colourless = No carbon dioxide is present Limewater becomes white and cloudy = Carbon dioxide is present
Physical vs Chemical Changes
Physical vs Chemical Changes Physical Changes Affects the form of a chemical substance, but does not alter the chemical composition You can separate mixtures by physical means such as melting, cooling, bending, stretching and other means Also includes phase changes
Physical vs Chemical Changes Phase changes Gas to liquid Liquid to gas Gas to solid Solid to gas Liquid to solid Solid to liquid Condensation Evaporation Deposition Sublimation Freezing Melting
Physical vs Chemical Changes Chemical Changes Changes the entire chemical composition of the substance
Chemical or Physical Change? Physical Chemical Physical
Signs of a Chemical Change What are some signs of a chemical change? 1. Precipitation (formation of a solid) 2. Release of gas (bubbles without heating) 3. Change in colour 4. Production of light 5. Release of heat
Types of Chemical changes Chemical changes involve chemical reactions We represent these in the form of equations Reactants Products The substances on the left are the reactants, and on the right are the products
Types of Chemical changes There are several different types of chemical reactions: Synthesis reactions Decomposition reactions Oxidation reactions Precipitation reactions
Synthesis Reactions When two or more substances combine to produce a new substance
Decomposition Reactions When a compound is broken down into two or more substances Basically the opposite of a synthesis reaction
Oxidation Reactions Any reaction where oxygen is one of the reactants One of these has to be O 2
Precipitation Reactions When two solutions are combined to form a new solid substance (the precipitate) that is insoluble in the solution Insoluble: cannot be dissolved