Chemistry Fundamentals: Solutions and Acids-Bases

Molarity

• Molarity is an international standard unit of measure that quantifies the amount of a substance dissolved in a solution.
• It is defined as the number of moles of a dissolved substance (solute) per liter of solution.
• One mole equals 6.022 x 10^23 entities (Avogadro's number).

Gas Phase Solutions

• Four variables are needed to define the physical state of a gas: temperature, pressure, volume, and the amount of gas (expressed as the number of moles).
• The ideal gas law quantifies the relationships between these variables.
• At standard temperature and pressure (STP) conditions (0°C and 1 atm), one mole of gas occupies 22.4 liters.

Chemical Reactions

• To determine how much gas is reacted or produced in a chemical reaction, four basic steps are needed:
  1. Write out the basic chemical reaction of interest.
  2. Find the number of moles of the reactant.
  3. Balance the chemical reaction by adjusting the stoichiometric coefficients (mole ratios) based on the number of moles of the key reactant.
  4. Convert moles of product to liters.

Limiting and Excess Reactants

• Not all reactants are consumed completely in a chemical process.
• The limiting reactant governs the amount of excess reactant that will be consumed and the amount of product that will be generated.
• The molar ratios aid in determining which reactant is limiting and which is excessive.

Percent Composition

• The percent composition of a compound indicates the percent by mass of each element present in it.
• It is calculated by dividing the total amount of an element by the molecular mass of the compound, multiplied by 100%.
• Empirical formula is the basic formula for expressing the proportion of elements that make up a compound.

Hydrates

• A hydrate is a compound that contains water (chemically bonded molecules).
• When a hydrate is heated, the hydrate loses its water and the substance that is left over is called the anhydrate.
• To determine the empirical formula of a hydrate, the "n", which is the number of moles of water, must be determined.

Dissolution

• Dissolution is when a solute dissolves into a solvent and forms a homogeneous mixture called a solution.
• Factors affecting the rate of dissolution include polarity, temperature, pressure, and surface area of the solute.

Electrolytes and Nonelectrolytes

• An electrolyte is a substance that breaks into ions and forms an electrically conductive liquid when melted or dissolved.
• Nonelectrolytes are substances that neither break into ions nor form an electrically conductive liquid when melted or dissolved.
• Electrical conductivity of electrolyte solutions depends on the concentration of solutes (ions) in solution.

Solubility Curve

• A solubility curve is a pictorial representation of the solubility of a solute in a solvent.
• It represents the solubility limits of a given mass of solute in grams at a specific temperature in degrees Celsius.

Salts

• A salt is a chemical formed after a reaction when the hydrogen from acid is replaced, at least partly, by a cation.
• Salts are ionic compounds with a cation and an anion, and some are soluble in water.

Concentration Units

• Molarity (M) is the concentration of a solution expressed in moles of solute per liter of solution.
• Molality (m) is the concentration of a solution expressed in moles of solute per kilogram of solvent.

Colligative Properties

• Colligative properties are properties of solutions that only depend on the ratio of solute and solvent present in the solution.
• The four colligative properties are boiling point elevation, freezing point depression, vapor pressure, and osmotic pressure.

Saturated Solutions

• A saturated solution is a homogeneous mixture in which the dissolved substance is in dynamic equilibrium with its undissolved form.
• The solubility of a solute is the concentration needed to make a saturated solution (its maximum possible concentration).

Synthesis and Decomposition Reactions

• A synthesis reaction is a reaction in which two or more substances combine to form a new compound.
• A decomposition reaction is a reaction in which a compound separates into its elements or compounds.

Arrhenius Acids and Bases

• Arrhenius acids and bases can be defined by a substance's behavior when dissolved in water.### Arrhenius Acids and Bases

• An Arrhenius acid contains hydrogen ions, which combine with water molecules to form hydronium ions when dissolved in water.

• Hydronium ions are the key component of an Arrhenius acid.

• An Arrhenius base exists when a substance is dissolved in water and creates a hydroxide ion in the product.

Properties of Arrhenius Acids and Bases

• Arrhenius acids: react with bases, have pH values between 0 and 7, taste sour, smell sour, and turn litmus paper red.
• Arrhenius bases: feel slippery to the touch, taste soapy, have pH values greater than 7, and turn litmus paper blue.

Examples of Arrhenius Acids and Bases

• Notable Arrhenius acids: HCl, HBr, HI, and HF.
• Notable Arrhenius bases: NaOH, KOH, and LiOH.

Limitations of the Arrhenius Definition

• The need for water to be present in order to dissociate into either hydronium or hydroxide is a limitation of the Arrhenius definition.

Other Definitions of Acids and Bases

• Bronsted and Lowry defined an acid as any substance that can donate a proton and a base as any substance that can accept a proton.
• Lewis defined an acid as a substance that accepts an electron pair to form a covalent bond, and a base as a substance that donates an electron pair to form a covalent bond.

Acid-Base Reactions

• An acid-base reaction involves the reaction between an acid and a base to form their respective conjugate acid and conjugate base.
• There are four acid-base reaction conditions: strong acid-strong base, strong acid-weak base, weak acid-strong base, and weak acid-weak base.

Acid-Base Neutralization Reactions

• A neutral solution is formed when acids and bases of equivalent strength react quantitatively.
• Examples of real-life acid-base neutralization reactions: breathing into lime water, hydronium ion reaction with hydroxyl ion to form water, and baking powder in cookies.

Autoionization of Water

• Water molecules can ionize other water molecules to form hydronium ions and hydroxide ions.
• The equilibrium constant for the autoionization of water is called the Kw constant, and is 10^-14 at 25°C.
• The Kw constant allows us to determine the range of the pH scale.

pH Scale

• The pH scale ranges from 0-14.
• When the scale reads from 0-6, the solution is considered acidic.
• When the solution measures between 8-14, the solution is considered basic.
• When the scale measures a solution at 7, the solution is considered neutral.

Calculating pH

• pH can be calculated using the formula: pH = -log[H+].
• pH is the negative log of the hydrogen ion solution.
• pH can never be negative.