Chemistry: Chemical Changes

Limewater + Carbon Dioxide Yields Calcium Carbonate (chalk) + Water

Baking Soda + Vinegar Yields Carbon Dioxide + Water + Sodium Acetate + Carbonic acid

Phenolphthalein/Water and Baking Soda mixed together then add Calcium Chloride! Wow!

Chemical changes result in the formation of one or more new substances with new chemical and physical properties. Evidences that a chemical change may have occurred include: 

● Color change 

○ When a substance changes color, the chemical composition of the substance may have changed (for example, iron turns to a reddish-brown when it rusts, clothes change color when bleach is added, apples turn brown when they react with oxygen in the air, or marshmallows turn black when burned). 

○ It is possible to have a color change without a chemical change (for example, adding food coloring to water). 

● Temperature change 

○ When a substance is combined with another substance, there may be an increase or decrease in temperature (for example, when wood burns to ash and gases, the temperature increases). 

○ It is possible to have a temperature change without a chemical change usually due to a heat source (for example, warming of the water in a pot). 

● Formation of a precipitate 

○ When two solutions are combined, they may form a new solid substance. This solid substance is called a precipitate and indicates that a chemical change has occurred. 

○ For example when carbon dioxide is combined with aqueous calcium hydroxide (limewater), solid calcium carbonate (chalk) is formed as the precipitate. 

○ The precipitate may be in the form of very small particles, appearing as cloudiness in the solution or as a solid which settles to the bottom of the container. 

● Formation of a gas 

○ When solid or liquid substances are combined, they may form gas bubbles or smoke indicating that a chemical reaction has taken place.

○ For example when vinegar is added to baking soda, it forms carbon dioxide bubbles. 

○ It is possible to form gas without a chemical change (for example, when water is heated to boiling). 

Chemistry: Physical Changes

Physical changes do not change the composition of a substance, only the physical properties. 

Evidences of a physical change include: 

● Change in state of matter 

○ When a substance changes from one state of matter to another (for example, changing from solid to liquid, from liquid to solid, or from liquid to gas), the composition of the substance remains the same. 

○ Examples of change in state might include: melting of ice cream, hardening of melted wax, or evaporating of water from wet clothes. 

● Change in size or shape 

○ When a substance changes in size or shape (for example, cutting, tearing, dissolving, stretching, or wrinkling), its composition remains the same. 

○ Examples of change in size or shape might include: shredding paper, dissolving sugar in water, stretching a rubber band, wadding up a piece of paper, or denting a piece of metal. 

Chemistry: Chemical Properties

Chemical properties can be recognized only when substances react or do not react chemically with one another, that is, when they undergo a change in composition. 

The following chemical properties can be used to help identify a substance: 

The ability of a substance to rust is a chemical property that involves a substance reacting slowly with oxygen. The process is called rusting.

The ability to burn involves a substance reacting quickly with oxygen to produce light and heat. This process is called burning.

Chemistry: Element Lab

Physical and chemical properties can be used to classify and identify substances. 

Metals and nonmetals are two major groups of elements that have different physical properties. 

 Physical properties of metals include: 

● Luster—Having a shiny surface or reflecting light brightly 

● Conductors—Heat and electricity move through them easily 

● Malleable—Ability to be hammered into different shapes 

● Ductile—Ability to be drawn into a wire 

● High density—Heavy for their size 

 Physical properties of nonmetals include: 

● Dull—Not shiny 

● Nonconductors—Heat and electricity do not move through them easily 

● Brittle—Break or shatter easily (solids) 

Physical properties can be observed and measured without changing the kind of matter being studied. The following physical properties can be used to help identify a substance:

Melting Point: 

● The temperature at which a solid can change to a liquid 

● Unchanging under constant conditions 

● Example: Ice melts to form liquid water at 0 oC (32o F). 

Boiling Point: 

● The temperature at which a liquid changes from a liquid to a gas. 

● Boiling begins when bubbles form throughout, grow larger, rise to the surface, and burst. 

● As long as the substance is boiling the temperature of the liquid remains constant (at the boiling point). 

● Boiling point is unchanging under constant conditions for a given substance. 

● Example: The boiling point for pure water at sea level is 100oC ( 212o F). 

Density: 

● The relationship between the mass of a material and its volume 

● Substances that are denser contain more matter in a given volume

●The density of a substance is unchanging no matter how large or small the sample of the substance. 

● Example: ○ Lead is a very heavy, dense metal. The density of lead is much greater than the density of the very light metal, aluminum. ○ Generally, metals have a heavier density than nonmetals. 

Conductivity: 

● The ability to act as an electrical conductor or an electrical insulator is based on the solid’s ability to complete an electric circuit, i.e., conduct electricity. 

● Materials with high conductivity are called electrical conductors because they allow current to flow easily. 

● Materials with low conductivity are called electrical insulators (nonconductors) because they do not allow current to flow. 

● Example: Most metals are electrical conductors while nonmetals are electrical insulators. 

Color: 

● Color can be used to help identify a substance, along with other properties. 

● By itself, color is not a significant identifier of a substance. 

● Absence of color is also a physical property. 

Hardness: 

● The relative resistance of a metal or other material to denting, scratching, or bending. 

Magnetism:

● The property of reacting to the forces exerted by magnets 

Chemistry: Matter

Elements
● Elements are pure substances that cannot be changed into simpler substances.
● Elements are composed of one kind of atom.
● Examples: Hydrogen, Oxygen, Carbon

Compounds
● Compounds are pure substances that are composed of two or more atoms that are chemically combined.
● Compounds can only be changed into simpler substances called elements by chemical changes.

Mixtures
● Mixtures are composed of two or more different substances that retain their own individual properties and are combined physically (mixed together).
● Mixtures can be separated by physical means (filtration, sifting, or evaporation).
● Mixtures may be heterogeneous or homogeneous.
          ○ In a heterogeneous mixture, which is not uniform throughout, the component substances can be visibly distinguished.
          ○ In a homogeneous mixture, which is uniform throughout, the substances are evenly mixed and cannot be visibly distinguished. The particles of the substances are so small that they cannot be easily seen. Another name for a homogeneous mixture is a solution. Examples: Rock, Air, Blood, Italian Salad dressing, Ocean water

Chemistry: Periodic Table of Elements

Atoms

●The atom is composed of subatomic particles: protons, neutrons, and electrons that affect the properties of an atom. 

● Protons and neutrons have about the same mass. 

● Protons have a positive charge, while neutrons have no charge. 

● Electrons have a negative charge. 

● Protons and neutrons are tightly bound in a tiny nucleus. 

● The nucleus is located in the center of the atom with the electrons moving in random patterns in the space around the nucleus.

The Periodic Table

●The periodic table is used to organize all of the elements. 

● Every periodic table will have a square for each element with the element name, chemical/element symbol, atomic number, and atomic mass.

Chemical/element symbols 

● Each element has a different symbol. 

● Symbols are written with one, two, or three letters. 

●The first letter is always capitalized. 

Atomic Number 

● The atomic number of an element is equal to the number of protons. 

● The atomic number is a whole number. 

● The atomic number is always the same for a given element. 

● The elements on the periodic table are arranged numerically by increasing atomic number. 

Atomic Mass 

● The atomic mass is an average sum of the number of the protons and the number of neutrons in the nucleus of the atom. 

● Since the atomic mass of an element is an average, it is usually not a whole number. 

Periods 

● A horizontal row on the periodic table is called a period. 

Families/Groups

● Families, also called groups, are vertical columns of elements on the periodic table 

● They are numbered 1-18. 

● Elements in the same family have similar properties. 

Metalloids 

● There is a zigzag line on the right side of the periodic table that separates the metals from the nonmetals. Metalloids are found along this zigzag line. 

● Elements identified as metalloids have properties (characteristics) of both metals and nonmetals. 

Metals 

● Metals are generally located on the left side of the zigzag line. 

● Examples of metals are: Sodium (Na), Calcium (Ca), Iron (Fe), and Aluminum (Al). ● The majority of elements are metals. 

Nonmetals 

● Nonmetals, with the exception of Hydrogen (H), are located on the right side of the zigzag line on the periodic table. 

● Examples of nonmetals are: Chlorine (Cl), Oxygen (O), Sulfur (S), and Iodine (I).

Periodic Table Battleship:

Chemistry: Indicators - pH paper, litmus paper, and phenolphthalein

Litmus paper 

 Has a special dye on it that changes colors in the presence of an acid or base. 

 Blue litmus paper turns red in an acid, and stays blue in a base. 

 Red litmus paper turns blue in a base, and stays red in an acid. 

Phenolphthalein 

 Is used to test for the presence of a base. 

 It is a colorless chemical that turns magenta (bright pink) in a base, and stays colorless in neutral or acidic solutions. 

pH paper

Has a range of colors depending on the pH of the solution. 

 The color of the paper is compared to the chart on the vial to determine the pH.