Understanding Hydrogen Bonds

• Hydrogen bonds are attraction forces between polar molecules.
• It's an attraction between hydrogen atoms bonded with nitrogen, oxygen, or fluorine, and another molecule containing nitrogen, oxygen, or fluorine.
• Hydrogen bonds occur only between water molecules.
• A hydrogen bond is stronger than a covalent bond. It can occur between NH3 and H2O, resulting from strong attractive forces.
• It results from strong attractive forces in ionic compounds

Physical properties

• Hydrogen bonds contribute to high melting and boiling points.
• Hydrogen bonds are stronger than Van der Waals forces.
• The presence hydrogen bonds means more heat energy is needed to overcome them during melting or boiling, thus they increase melting and boiling points
• Covalent molecules like NH3, HF, HCl, and C2H5OH dissolve quickly in water.
• A dative bond shares electron pairs originating from a single atom.
• Example: +O2 and Nitrogen, where a pair of valence electrons are not involved.
• H2O forms a hydroxonium ion, and ammonium ions.

Metallic Bonds

• Metal atoms arrange closely in layers.
• Each metal donates valence electrons to form positively charged ions.
• These electrons don't belong to any one metal atom.
• Valence electrons are delocalized and move freely around the metal structure.
• Electrostatic forces between positive metal ions and the "sea" of electrons form the metallic bond.

Electrical Conductivity of Metal

• Metals conduct electricity in the "sea" of electrons.
• Ionic and covalent compounds have differing electrical conductivity.
• Ionic compounds conduct when molten. Something has to be free to move.
• Metallic compounds have lower melting points and are volatile.

Acids and Bases

• Acids are chemical substances that ionize in water, producing hydrogen ions (H+).
• Alkalis (bases) are soluble in water and ionize to produce hydroxide ions (OH-).
• Bases ionize in water, producing hydroxide ions (OH-).

The Role of Water in Acids and Bases

• Acids ionize in water to form hydronium ions, turning litmus paper red.
• Strong acids ionize completely in water, such as HCl, H2SO4, and HNO3.
• Weak acids ionize partially in water, like ethanoic acid, phosphoric acid, and carbonic acid.
• Alkalies ionize in water to form hydroxide ions, turning litmus paper blue.
• Strong alkalies ionize completely in water. (NaOH, Ba(OH)2, KOH.)
• Weak alkalies ionize partially in water such as NH3.

pH Values

• Acids have a pH value between 0 and 6.
• A higher concentration of H+ ions means a lower pH value.
• The equation for pH is pH = -log10[H+].
• [H+] = 10-pH
• Alkalines have a pH value between 8 and 14.
• A higher concentration of OH- ions means a higher pH value.
• The equation for pOH is pOH = -log10[OH-].
• [OH-] = 10-pOH

Acidic Solution Dilution

• When an acidic solution is diluted:
  • the concentration of H+ ions decreases
  • the pH value increases
  • the degree of acidity decreases

Chemical Properties

• Acid+reactive metal -> salt + H2
• Acid + base -> salt + water
• Acid + metal carbonate -> salt + H2O + CO2
• Alkali + acid -> salt + H2O
• Alkali+ammonium salt -> salt + H2O + Ammonia gas
• Alkali+ metal ion -> metal hydroxide

Concentration of Aqueous Solutions

• A solution is a mixture formed by dissolving a solute in a solvent.
• The equation for a solution is: solute + solvent = solution.
• Concentration is the quantity of solute in 1 dm3 of solution.
• Molarity = number of moles of solute present in 1 dm3 of solution.
• Molarity formula is: number of moles of solute divided by volume

Preparing a Standard Solution

• Weighing method: involves calculating the mass of solute needed for a specific concentration and volume.
• Dilution method: determine moles of solute, add water to change concentration
• Solid substances to prepare include hydrated oxalic acid, anhydrous sodium carbonate.
• NaOH not used when preparing standard solution. It reacts with CO2 in air and absorbs water from the atmosphere
• M1V1 = M2V2 can be used for both standard solutions and neutralizations

Neutralization (Acid-Base Reactions)

• Neutralization is an ion reaction between a base and an acid.
• acid + alkali -> salt +water which is also H+ + 0H- -> H20
• Spectator ions (Na+, Cl-) from eliminate
• The ionic equation is: H+ + OH- → H2O
• An acid reaction combines with on ion from an acid combine with on ion from alkaline

Acid-Base Titration

• This is used to determine the concentration of an acid or alkali of unknown concentration.
• Appropriate indicators include:
  • litmus
  • methyl orange
  • phenolphthalein
  • UI

Applications of Acid-Base Titration

• Compost: to neutralize acidity or alkalinity.
• Agriculture: to manage soil pH.
• Fertilizer production: to measure percentage of nitrogen.
• Medicine: use of antacids for indigestion.
• Industry: in electroplating, energy production, and chemical synthesis.
• Salt: an ionic compound formed when H+ ion in the replaced by a metal/ammonium ion

Salt Properties

• A salt crystal is formed by replacing the H+ in an acid w/ metal ion or ammonium ion
• Physical properties of crystalline salts.
  • fixed geometrical shape
  • flat faces