Chemistry II

Properties of Acids and Bases

Acid - a substance that promotes a chemical change and creates salt water with a base.

Base - any substance that causes chemical change and creates salt water with an acid.

Acids

• Acids ex. Vinegar, Lemon Juice (anything ending in acid obviously)

• Acids are corrosive; the more acidic (lower pH), the more corrosive

• Greater concentration of hydronium ions than hydroxide ions

• When aqueous, water is the solvent, and electric currents can be conducted

• When mixed with metals, it releases H2

• Blue litmus paper will turn red if a substance is an acid

Bases

• Bases ex: Baking Soda, anything that ends in hydroxide, blood, detergents

• Chalk, Bleach, Soap

• Greater concentration of hydroxide ions than hydronium ions 

• Often found in cleaners (very effective at removing grease and disinfecting)

• Found in many natural and Artificial flavorings

• Used to help neutralize the properties of an acid

• Bases are corrosive and can conduct electricity while also being able to neutralize acid’s properties.

• An indicator is a compound that changes color at different pH ranges when it reacts with acidic or basic solutions - it can tell you a rough estimate of the pH of your solution. 

• Red litmus paper will turn blue if a substance is a base

pH Scales and Indicators

pH Scale: stands for potential of hydrogen. A scale for measuring how acidic or basic an aqueous substance is

• Invented by Soren Peter Lauritz Sorensen in 1923

• 0-6= Acid (low pH)

• 8-14 = Base (high pH)

• 7 = neutral substance (water)

pH-  the measure of how acidic or basic water is.

pH indicators - solutions that are used to measure the approximate pH of a substance. These will change colors when mixed with a substance to symbolize the pH of that liquid

3 Ways to Measure pH Levels

1. pH Indicators - Using another liquid chemical to cause a reaction to estimate acidity

2. pH Testing Strips - Strips containing an indicator that changes color depending on the pH value

3. pH Meter - An electronic instrument with an electrode that is sensitive to the acidity of a solution

pH Meters are the most accurate/effective

Ionic Bonds

Key Things to Know:

• Ionic compounds typically have high melting and boiling points because they are strongly (electrostatically) attracted

• Metals first, non-metals second

• Metals form cations, or positive ions, since they are giving away electrons

• Nonmetals form anions, or negative ions, since they are gaining electrons

• Removing electrons = positive (+) charge

• Adding electrons = negative (-) charge

• When atoms exchange electrons, they have opposite charges

• Since opposites attract, they electrostatically bond

Valence Electrons - the key to bonding

An ionic bond is where valence electrons are transferred from one atom to another. (they like it very much when they get 8 valence electrons)

Ex.

Sodium -> one valence electrons

Chlorine -> seven valence electrons

Metals like to give away electrons, and nonmetals like to receive electrons

Sodium gives chlorine one valence electron, acquiring a positive charge and giving chlorine a negative charge.

Like charges repel, but opposite charges attract

Sodium and Chlorine form an ionic bond because of the electrostatic attraction between opposite charges

When Naming:

• Metals always come first in the name 

• Non-metals always are on the left (second)

EXAMPLE:

 Potassium + Chlorine = Potassium Chloride

• Potassium is first, it is the metal

• Chloride is second, it is a non-metal

• Notice how chloride ends in “ide.”

• 
  Chemical Reactions

  
  

  Signs of Chemical Reactions:

  • Change in temperature

  • Change in color

  • Bubbles (NOT boiling)

  • Formation of a precipitate (when a mixture of two liquids creates a solid)

  • Light (burning)

  • Smell/odor

  • The change is difficult to reverse

  
  

  *Physical changes are easier to reverse than chemical changes

  • In chemical reactions, a new substance is created

  • The substance has new physical AND chemical properties

  
  

  How to Speed up Chemical Reactions:

  • Lowering the volume of a reaction mixture/vessel (lesser amount of substances to react)

  • Increasing the number of particles (more concentration)

  • Temperature => faster-moving particles => speed up chemical reactions (molecules are more likely to bump into each other)

  • No clumps to increase surface area

  • Chemical catalysts lower the energy required for a reaction (lower the activation energy)

  
  

  *For a Chemical Reaction, particles must collide with the right orientation and enough energy

  
  
  

  Vocabulary:

  
  
  

  Physical property - A characteristic of matter that can be observed or measured without changing the identity of the matter (boiling point, density, surface tension, viscosity, color)

  
  

  Chemical property - A characteristic of matter that can only be observed when a substance is undergoing a chemical reaction (flammability, reactivity, acidity)

  
  

  pH - the measure of how acidic or basic an aqueous substance is.

  
  

  Chemical Reaction: a process in which atoms of one or more substances rearrange to form one or more new substances with new chemical AND physical properties.

  
  

  Atom - a small particle that is the building block of matter.

  
  

  Chemical Equation - a description of a reaction using element symbols and chemical formulas.

  
  

  Mass - the amount of matter in an object.

  
  

  Periodic Table - a chart of the elements arranged into rows and columns according to their physical and chemical properties.

  
  

  Law of Conservation of Mass - the law that states that matter can neither be created nor destroyed

  
  

  How does the Law of Conservation of Mass apply to chemical reactions? The total mass of the reactants before a chemical reaction is the same as the total mass of the products after the chemical reaction

  
  

  During a chemical reaction, atoms of elements or compounds rearrange and form different elements or compounds.

  
  

  • Atoms rearrange when connections between atoms break

  
  

  • Chemical formulas represent compounds

  
  

  • A chemical equation includes the substances that react and those that are formed in a chemical reaction

  
  

  • The starting substances in a chemical reaction are reactants 

  
  

  • The substances produced by the chemical reaction are products.

  
  
  
  

  The breakdown of one reactant into two or more products is one type of chemical reaction. Each type of chemical reaction follows a unique pattern in the way atoms in the reactants rearrange to form products.

  
  
  

  Combustion

  A chemical reaction in which a substance combines with oxygen and releases energy. Usually released as thermal and light energy. (usually something burning)

  
  
  

  Synthesis

  Chemical reaction in which two or more substances combine and form one compound. 

  (Ex: Mg reacts with Oxygen (O2) in air and forms magnesium oxide (MgO)

  Recognize two or more reactants form only one product

  
  

  Decomposition

  One compound breaks down and forms two or more substances. 

  (Ex: H2O2- Hydrogen Peroxide decomposes and forms water and oxygen gas H20 and O2)

  Recognize one reactant that forms two or more products 

  
  

  Replacement

  When an atom or a group of atoms replaces part of a compound. 

  
  

  Two types of replacement:

  
  

  1. Single replacement - one element replaces another element in a compound; an element and compound react and form a different element and different compound in this reaction

  
  

  2. Double replacement reaction - two elements switch places, forming two new compounds- two compounds react and form two new compounds in this reaction

Counting Atoms

1. The symbol of an element represents one atom of that element.

• Example: Ba=         Barium        )  

2.  A subscript is a number written in the lower right corner behind the symbol of an element. If there is more than one atom of the element, then a subscript is used to indicate the number of atoms. 

• Example: Cl₂ =      Cl = 2       )

3.  A subscript outside a bracket multiplies all the elements inside the brackets. 

• Example: Ca₃(PO₄)₂ = 

• Ca =     3_ 

• P =    2 _ 

• O =     8_ 

4.  A coefficient is a number written in front of a chemical symbol and indicates the number of atoms of that element or number of molecules.

• Example: 

  • 3C =         coefficients 

  • 2NaSO₄ =     Na = 2         S = 2            O = 8    .

5. A subscript is a number written after an atom in a formula and indicates the number of atoms of that kind in the molecule. 

• Example: 

  • H₂SO₄ The subscript of H = 2 and the subscript of O =    4   .

NOTE: A coefficient multiplies the number of atoms of each element in the formula

Balancing Chemical Equations

What does it mean to have a “balanced” chemical equation?

Mass of reactants = mass of products (same number and type of atom).

Balancing the equation in 3 easy steps! 

1. Count the total number of atoms of each element on the product AND reactant sides.

2. Adjust coefficients (the big numbers in front) in front of molecules until the number of atoms of every element matches on both sides

3. Check the equation by counting the number of atoms of every element on both sides. Once the number of atoms for each element matches on both sides, the equation is balanced.

Law of Conservation of Mass

States that matter can neither be created nor destroyed.

Mass is conserved in a reaction because atoms are conserved

Despite the rearrangement of atoms, the total number of atoms of each element stays the same on both sides of the chemical equation

Balancing Chemical Equations

Must have an equal amount of each atom on each side

How to balance

Count the atoms in the reactants and the products and then add coefficients to balance the number of atoms. A coefficient is a number placed in front of an element symbol or chemical formula, such as 2H20