Mixtures, Elements, Compounds and Atoms

Definitions

• A mixture consists of two or more pure substances not chemically combined.
• An element refers to a pure substance that cannot be simplified using chemical methods.
• A compound is a pure substance made up of chemically combined elements.
• Physical properties are determined without changing the substance.
• Chemical properties describe a substance's ability to react or change into another substance.
• A physical change does not produce new substances.
• A chemical change results in the production of new substances.
• An atom is the smallest part of an element that retains its chemical properties.
• An element comprises only one type of atom.
• A molecule is the smallest part of an element or compound that can exist independently in standard conditions.
• Isotopes are atoms of the same element with different numbers of neutrons.
• Relative isotopic mass is the mass of an atom of that isotope on the ¹²C = 12.0000 scale.
• Relative atomic mass is the weighted average of the relative isotopic masses of naturally occurring isotopes on the ¹²C = 12.0000 scale.
• An ionic bond involves strong non-directional electrostatic attraction between oppositely charged ions.
• An ionic bond forms through the transfer of one or more electrons from one atom (or group of atoms) to another.
• An ionic compound consists of ions and is electrically neutral.
• A metallic bond is a strong non-directional electrostatic attraction between delocalized electrons and metal ions.
• A covalent bond involves strong directional electrostatic attraction between shared electrons and the nuclei of bonded atoms; it forms by sharing outermost shell electrons between atoms.
• Molecular formulas show the actual number of each type of atom in a molecule.
• Structural formulas show how constituent atoms are linked in a molecule.
• A dative covalent bond occurs when both electrons of the shared pair come from the same atom.
• A mole is the amount of substance containing the same number of formula units as atoms in exactly 12.0 g of carbon-12.
• An acid is a covalent molecular compound that ionizes to give H+ as the only cation.
• A strong acid completely ionizes to give H+ ions.
• A weak acid slightly ionizes to give H+ ions.
• A base reacts with acid to give salt and water only.
• An alkali is a base that is soluble in water, reacting with acid to give salt and water only.
• A strong alkali completely dissociates in water.
• A weak alkali only slightly ionizes in water.
• An electrolyte conducts electricity when melted or dissolved in water.
• A standard solution has an accurately known molarity.
• The equivalence point in acid-alkali titration is where the acid and alkali have just completely reacted.
• The end point is where the indicator changes color sharply.
• A functional group is an atom or group of atoms responsible for most of a compound's chemical properties.
• A free radical is an atom or a group of atoms with at least one unpaired electron.
• Cracking is the process of breaking down large molecules (usually long-chain carbon compounds) into smaller ones.
• Electronegativity is the power of an atom in a molecule to attract bonding electrons.

Octet Rule and Energy

• The octet rule indicates that atoms tend to attain the stable electronic configuration of the nearest noble gas.
• The number of protons increases across a period, which can attract bonding electrons more effectively.
• The law of conservation of energy states that energy cannot be created or destroyed, only changed from one form to another, and the total energy of a system and its surroundings remains constant.
• Enthalpy change is the heat change of a reaction at constant pressure.
• Standard enthalpy change of combustion applies when one mole of a substance is completely burnt in oxygen under standard conditions.
• Standard enthalpy change of neutralization applies when one mole of water is produced from neutralization of an acid and an alkali under standard conditions.
• Standard enthalpy change of formation applies when one mole of substance forms from its constituent elements in their standard states under standard conditions.
• Hess's Law: The overall enthalpy change of a chemical reaction is the same, regardless of the route, provided that the initial and final states are the same.
• Avogadro's law states that equal volumes of gases contain the same number of molecules when measured at the same temperature and pressure.

Polymerization and Isomers

• Addition polymerization: Monomer molecules join repeatedly to form polymer molecules without eliminating small molecules.
• Condensation polymerization: Monomer molecules join repeatedly to form polymer molecules with the elimination of small molecules.
• Markovnikov's rule: In an addition reaction, when HX is added to an alkene, the H atom attaches to the carbon atom of the C=C double bond that already has the most H atoms.
• Isomers are molecules with the same molecular formula but different structural or spatial arrangements.
• Structural isomers have the same molecular formula but differ in the order of atoms.
• Stereoisomers have the same order of atoms but differ in their spatial arrangement.
• Enantiomers are molecules that are non-superimposable mirror images of each other.
• A detergent is a substance that enhances the cleaning properties of water.

Solutions and General Info

• A saturated solution contains the maximum amount of solute at a specific temperature.
• A saturated solution can be demonstrated by removing a drop with a glass rod; solid forms if any solute precipitates when the drop cools.
• Water purity is tested by observing its boiling point, which should be exactly 100°C under 1 atm.
• Atomic size decreases across a period.
• Atomic number increases, the number of protons in the nucleus increases, more electrons are added to the outermost shell, and electrons experience greater attraction from the nucleus across a period.
• Filtration setup involves a beaker with a solution, poured over a glass rod.
• Sulfur dioxide (SO₂) is tested using filter paper soaked with acidified potassium dichromate; the paper changes from orange to green.
• In experiments use a glass rod.
• In fractional distillation, carbon dioxide cannot be liquefied.
• Water in a test tube removes hydrogen chloride gas.
• Concentrated sulfuric acid is a drying agent.
• The accuracy of an experiment can be improved by lowering the concentration of the standard solution or increasing the mass of the sample.

Flame Tests and Limewater

• Flame test procedure:
  • Moisten a platinum wire with concentrated hydrochloric acid.
  • Dip the wire into a crushed sample.
  • Heat the end of the wire strongly in a non-luminous flame.
• Limewater preparation:
  • Dissolve excess calcium oxide in distilled water.
  • Filter the mixture and collect the filtrate, which is limewater.

Odor and Slanting Positions

• Odors can be removed if the volatile reactants convert into involatile products.
• Boiling tubes are clamped in a slanting position to prevent cracking from the backflow of cold condensed water.
• Keep the delivery tube's free end above the liquid to prevent sucking water back.

Safety and Reactions

• Excess hydrogen should be burned since it is flammable and explosive.
• Al₂O₃ cannot be determined through certain reactions.
• Aluminium is a stronger reducing agent than hydrogen; the oxide of aluminium cannot be reduced by hydrogen.
• Rusting is the reaction of iron with water and oxygen, forming a reddish-brown solid (hydrated iron(III) oxide).
• Rusting rate increases with: presence of acid, mobile ions, higher temperatures, and connection to less reactive metals.

Electroplating and Coatings

• Uneven surfaces increase rusting due to weaker metallic bonds.
• Metals are cleaned with organic solvents to remove grease and increase electrical conductivity for electroplating.
• Agar slows diffusion of blue patches around a nail for observation.
• Coatings made of metal or metal oxide protect iron from water and oxygen.
• Zinc, being more reactive, provides sacrificial protection to iron by losing electrons.
• Connect the object to the negative terminal of a D.C. source for cathodic protection.

Corrosion

• Anodization thickens the protective oxide layer on aluminum, preventing contact with oxygen and water.
• In anodization, connect the aluminum object to the positive terminal of a DC supply as the anode; use an aluminum sheet as the cathode, and dilute sulfuric acid as the electrolyte.
• Anodized aluminum can be easily dyed for attractive colors.

Carbon Reduction and Metals

• Extracting metals involves using a crucible lid, a crucible, a pipeclay triangle, and a mixture of metal oxide and coke, heated on a tripod.
• A precaution is to avoid heating wet sand directly: steam production may occur too quickly, pushing most products to cross through any metal that reacts.
• In metal reactions with steam, remove the delivery tube before stopping to prevent sucking back of water and damage to the tube.
• Hydrogen gas will only react with Magnesium to give H₂.
• Metallic bonds cause high melting points.
• The electrons experience greater attraction from the nucleus.
• The reaction of iron with water and oxygen gives a reddish-brown solid (hydrated iron(III) oxide).

Metal Reactions and Properties

• A metal oxide is more stable than B metal oxide signifies A is more reactive than B in reactions.
• Zinc oxide (ZnO) turns yellow when hot, and white when cold.
• Lead(II) oxide (PbO) is orange when hot, and yellow when cold.
• Metals have strong metallic bonds.

Acidic and Alkaline

• The heat released from a weak acid is lower than a strong acid because energy is reabsorbed.
• Precipitates that dissolve in excess sodium hydroxide include aluminum, zinc, and lead.
• Precipitates that dissolve in excess ammonia include silver, zinc, and copper.
• The basicity of an acid is the maximum number of hydrogen ions produced by one molecule.
• Carboxylic acids cannot be written as H⁺(aq).
• Nitric acid decomposition accelerates with light.
• The filter should contain the substance being analyzed and the added reagent is too slow.
• Diluting with water will cause the acid to splash since the acid is exothermic.
• Methyl orange indicator indicates a red colour from the acidic properties, a yellow colour for the alkaline properties.
• Add excess of carbonate/hydroxide to ensure there is no contamination.

Crystallization

• Heat to evaporate water to obtain a saturated solution.
• Let aside to room temperature and allow the water to cool slowly.
• This is because solubility decreases in this environment.
• Filter the crystals off and prevent any from being lost.

Standard and Hydrateds

• Preparing a stand solution can be done as follows:
  • Add known mass sodium Carbonate to a beaker.
  • Add what is dissolved in the distilled water to a volumetric flask.
  • Stopper the flask with contents well mixed.
• Hydrated salt turn color when heated strongly in a test tube.
• An acid soil can be diluted with slaked lime.
• An alkaline soil can be diluted with ammonium sulphate.
• Insoluble salt is dissolved in excess volume and known concentration of acid.
• The titration must be with known volume of acid and sodium hydroxide to make it dilute.

Organic Chemistry

• In a compound, the UV light is need to break the x-x bond.
• Methane products are formed from further substitution, where they are each the same general formula.
• Remnants are formed and subjected to heat for long time (petroleum and natural gas).
• Incomplete combustion and N2 reactions occur at high temperature.

Petroleum and Cracking

• Petroleum fractional distillation separates alkanes.
• The bottom ones have a higher temperature which condenses at different levels.

Fractional Distillation

• From top to bottom, increasing the gas by measuring vapor and at high temperature.
• Cracking with alenes makes a useful fuel

Alcohol Properties

• Water cannot be counted with
• The functional group is an akyalene group of alcohols
• Some reactions of alcohol are performed under high catalyst