C2: Chemistry

Annotations:

• Atoms: Mass number: top number, protons + neutrons Atomic number: bottom number, protons
• Compounds: One or two atoms formed together
• Isotopes: Different forms of the same element which have the same number of protons but a different number of neutrons

1. Ions and Formulas

   Annotations:

   • Groups that lose electrons: 1, 2 Groups that gain electrons: 6, 7 Gaining an electron becomes negative, Losing an electron becomes positive
   • Formulas: - Must have positively charged part, negatively charged part and then equal 0 Sodium Chloride:                               Na+ (+1) and Cl (-1)                          (+1) + (-1) = 0                                So it is balanced as NaCl                                           Magnesium Chloride:                         Mg2+ (+2) and Cl- (-1)                       (+2) + ( -1) = 1                                    So it is unbalanced and requires 2 Chloride atoms making MgCl2
2. Electronic Structure

1. Bonding

   Annotations:

   • Covalent Bonding: sharing electrons to make full outer shells and reach noble gas configuraton
2. Substances

   Annotations:

   • Simple Molecular Substances: - Very strong covalent bonds - Forces of attraction between molecules are very weak - Low melting and boiling points - No ions or electrical charge so do not conduct electricity
   • Giant Covalent Structures (Macromolecules): - Similar to lattices but no charged ions - All atoms strongly covalently bonded - Very high melting and boiling points - Do not conduct electricity (except molten graphite) - Examples are graphite and diamond

Annotations:

• - Giant structure - Sea of free (delocalised) electrons coming from the outer shell of every metal atom in the structure - This allows good conduction of heat and electricity - Electrostatic attraction between positive metal ions and negative electrons - Allow layers to slide over each other
• Alloys: - Stronger - Mixture of two metals - Distorts structure stopping layers from sliding over each other

Annotations:

• Smart Materials: - Behave differently depending on the conditions - Have remembered shapes that can go back to after being bent
• Nanoparticles: - Tiny particles - Fullerenes Fullerenes can be used to make nanotubes
• Nanotubes: - Huge surface area to volume ratio (catalyst use) - Use as sensors - Stronger, lighter building materials - Don't leave white marks in suncream or deodorant - Absorbed easier; drug use - Lubricant use - Conductors could be used in electric circuits

1. Relative Formula Mass

   Annotations:

   • Relative Atomic Mass: How heavy different atoms are in relation to carbon-12 in Ar
   • Relative Formula Mass: All the relative atomic masses added together MgCl2 --> 24 + (35.5 x 2) = 95Mr
   • Moles: Equal to its Mr in grams Mr x Moles = Mass (g)
2. Formula Mass Calculations

   Annotations:

   • Percentage Mass of an Element in a Compound: Ar x No. of atoms  /                    Mr (of compound)                    then x 100                             
   • Empirical Formula: Experimental mass  /                     Ar                                                   then x 10                                    then /4   Then the two numbers you get are put to the right side of the element in the abbreviated equation                                                                                         
3. Calculating Masses in Reactions

   Annotations:

   • Work out Mr then divide or multiply accordingly

Annotations:

• Percentage Yield: Comparing the actual and predicted yield Actual yield (g) /                             Predicted yield (g)                          then x 100 Shows the overall success of the experiment
• Reversible Reactions: You never get a 100% yield, reactants are always lost, this happens particularly in reversible reactions as the reactant never completely change ammonium chloride <--> ammonia + hydrogen chloride

Annotations:

• Exothermic: Energy is transferred to the surrounding usually in the form of heat and usually shown by a rise in temperature (e.g. combustion) - Oxidisation - Neutralisation
• Endothermic: Energy is taken in from the surroundings usually in the form of heat and usually shown byy a fall in temperature - Less common - Thermal decompositions: heat + calcium carbonate decomposes to make quick lime
• Can be reversible: hydrated copper sulphate --> anhydrous copper sulphate + water (ENDOTHERMIC) anhydrous copper sulphate + water --> hydrated copper sulphate (EXOTHERMIC)

Annotations:

• pH scale: 1-2-3-4-5-6-7-8-9-10-11-12-13-14 Acids  ...  Neutral      ...     Alkalis  Red    ...  Green        ...     Purple Indicator: dye that changes colour
• Bases: Alkali is a base that dissolves in water Bases and acids neutralise
• Acids: H+ ions Alkalis: OH- ions Acid + base --> salt + water State symbols: (s) - solid, (l) - liquid, (g) - gas, (aq) - dissolved in water {aqueous}

Annotations:

• Acid + metal --> salt + hydrogen Hydrochloric acids produce chloride salts Sulfuric acids will always product sulfate salts Nitric acids produce nitrate salts when neutralised but with metals it can produce nitrogen oxide.

Annotations:

• Combination of meatl and acid names the salt e.g. hydrochloric acid + copper oxide -->  copper chloride

1. Oxides

   Annotations:

   • Acid + metal oxide --> salt + water
2. Hydroxides

   Annotations:

   • Acid + metal hydroxide --> salt + water
3. Ammonia

   Annotations:

   • Can be neutralised with HNO3 to make fertiliser Ammonia dissolves in water to produce an alkaline solution, when reacted with nitric acid you get a neutral salt - ammonium nitrate NH3 (aq) + HNO3 (aq) --> NH4NO3 (aq) [no water is produced]

1. Ionic

   Annotations:

   • Bonding: - Atoms lose or gain electrons to form charged particles (ions) - Shells with one electron lose it, shells with one electron off noble gas configuration gain one
   • Compound Structure: - Giant regular lattice - Very strong electrostatic forces of attraction between oppositely charged ions
   • Compound Properties:- High melting points (due to strong attraction between ions)- High boiling point (due to strong attraction between ions) - Ions freely move and carry electric current when compound is melted - Dissolve easily, similar reaction to melting
2. Covalent

   Annotations:

   • See Covalent; Bonding

Annotations:

• Properties of Plastics: Bonds between different molecules  determine the properties of the plastic Weak Forces: - Individual tangled chains of polymers, held by weak intermolecular forces are free to slide over each other Strong Forces: - Crosslinks hold the chains firmly together The properties are determined by the starting materials and reaction conditions

Annotations:

• Paper Chromatography: Artificial colours can be separated using paper chromatography where it runs through solvent
• Machines: (Instrumental methods) Advantages: - Very sensitive - Very fast and can be automated - Very accurate
• Gas Chromatography: Used to identify substances - Gas carries substances through column - Different speeds separate them - Time taken to reach detector (retention time) recorded - Graph is drawn to show peaks when substances arrive - Mass spectrometer also identifies substance as they leave the column - Graphs show relative molecular mass

Annotations:

• Affecting Factors: - Temperature - Concentration - Use of catalysts - Surface area (of solids) - Pressure (of gases)

1. Measuring Reaction Rate

   Annotations:

   • Measuring how quickly a product is made or how quickly the reactants are used up Rate of reaction =                              Amount of reactant used or product formed/ Time
   • Precipitation: "X" under beaker and the quicker clouds cover the "X" the quicker the rate of reaction
   • Change in Mass: Measure how much gas was given off by weighing the beaker throughout the whole reaction, the quicker the mass drops, the quicker the reaction rate
   • The Volume of Gas Given off: Use a gas syringe to measure the amount of gas given off, the more gas given off in a time interval, the quicker the rate of the reaction
2. Collision Theory

   Annotations:

   • More collision = faster reaction Temperature: particles gain energy and move more Concentration/Pressure: particles closer Surface Area: separates particles
3. Reaction Rate Experiments

   Annotations:

   • Hydrochloric Acid and Marble Chips:Measure carbon dioxide given off using a gas syringeBreak up marble chips each time, eventually using powdered chalk Graph: x = time, y = amount of gas evolved
   • Magnesium Metal and Dilute Hydrochloric Acid:Use a mass balance (scales) to measure amount of hydrogen gas given off Repeat with increased concentrations Graph: x = time, y = loss in mass
   • Sodium Thiosulfate and Hydrochloride Acid: Use paper marked with an "X" that will disappear due to the yellow and cloudy precipitate formed This can be done at different temperatures Graph: x = time taken for mark to disappear, y = temperature
   • Decomposition of Hydrogen Peroxide: 2H2O2 (aq) --> 2H2o (l) + O2 (g) Usually quite slow but Manganese(IV) oxide catalyst speeds it up. Could also use potato peel or blood Use a gas syringe to measure the oxygen gas given off Better catalysts give steeper graphs on the graph: x = time, y = volume of gas given off
4. Catalysts

   Annotations:

   • A substance which speeds up a reaction, without being changed or used up Solid catalysts give a surface to stick to increasing successful collisions
   • Reducing Costs:- Less energy needed- Can work it at a much lower temperature - Reuse them
   • Disadvantages:- Expensive - Specific for certain reactions - Poisoned by impurities

1. Electrolysis of Sodium Chloride
2. Aluminium Extraction
3. Electroplating