chem yr 10 exam

Chemistry yr 10 exam prep


Organic chemistry 


Crude oil (unprocessed oil)

  • Created from the remains of tiny sea animals and plants ( its a fossil fuel)

  • A mixture of hydrocarbons with different chain lengths


Fractional distillation

  • Separation of crude oil into useful fractions with similar boiling points

E.g. petrol, kerosene, diesel 

  • Less intermolecular force (shorter molecule) means less energy to break apart into a gas and lower boiling point

  • Crude oil heated so it turns to vapor form and can be pumped into the colom that is hot at the bottom and cool at the top

  • Small molecules with low boiling points condense much higher in the colom where it's cooler than large molecules with larger molecules therefore hydrocarbons with similar boiling points are collected in the same tray


Fractions: mixtures of hydrocarbons with similar boiling points


Hydrocarbons

  • Simplest organic molecule (4 covalent bonds)


homologous series: family of hydrocarbon molecules in which each member has 1 extra carbon and 2 extra hydrogen atoms from a previous member of the series


Alkane homologous series

  • Saturated hydrocarbon because bonded with 4 other atoms

e.g.

  • Methane                                 - ethane

  • Propane                                  - butane

  • Pentane                                  - hexane

  • Heptane                                  - hexane

  • Nonane                                   - decane



Alkene

  • Each member has one double bind within the carbon chain

  • Unsacturated as carbon atoms bonded to less than 4 other atoms


Alkynes

  • Each member has one triple bind within the carbon chain

  • Unsacturated as carbon atoms bonded to less than 4 other atoms


Naming Hydrocarbon branches

Steps to follow:

1.  Identify the longest carbon atom chain in the molecule (if an alkene or alkyne the longest chain chain must include the double or triple bond). This tells you the main stem name for the molecule.

2.  Number the C atoms in the longest chain, starting from the end closest to the side chains.

3.  Side chains are given a name ending with the suffix ‘-yl’ (eg -a one carbon side chain is called ‘methyl’, a two carbon side chain is ‘ethyl’)

4.  Each side chain is given a number to show to which carbon in the main chain it is attached.


Isomers

  • Molecules with same molecular formula but different structural formula


Hydroxyl functional group

  • Contains oxygen and hydrogen atom joined by a single covalent bond

  • Hydroxyl attached to alkane material referred to as an alkonol


Analytical chemistry 


Gravimetric analysis

  • Quantitative analysis of substances based on the measurement of mass

  • Used to measure the concentration of an analyte (substance to be analysed) in a sample

  1. Sample is weighed

  2. Sample is heated to evaporate water

  3. Sample is cooled in a dessicator

  4. Sample is reweighed

  5. Step 2 - 4 is repeated until constant mass obtained so the experiment is accurate


  • Errors that could occur is incomplete precipitation 


Specialised glassware and dilution

  • Burettes: accurately measure volume of one solution into another, read from bottom of meniscus

  • Pipettes: accurately dispense a known volume of solution


Meniscus: curved surface if liquid container


Volumetric analysis


Accurate data

  • degree to which a measurement is close to its true value


Precise data

  • degree to which repeated measurements are close to each other


Indicator solution in volumetric analysis

  • Used to visually signal the end point of a reaction


General science skills


Fair test

  • One variable changed at a time whilst all other are kept constant

  • Experiment should be repeated to ensure results are reliable


Systematic error

  • Consistent, repeatable inaccuracy by a faulty instrument or experiment flaw

Random error

  • Unpredictable fluctuation due to chance or uncontrolled variables


Chemical reactions


Types of chemical reactions

  • Combustion

  • Decomposition

  • Combination

  • Precipitation

  • Displacement 


Specific reactions

  • Neutralisation

  • Acids and metals

  • Acids and carbonates 


Steps to use when writing and balancing equations:

  1. Write the word equation

  2. Write the unbalanced equation by replacing the chemical names with chemical formula

  3. Write down the number of atoms that there are for each element on each side of the equation

  4. Place coefficients in front of each reactant and product to balance the number of atoms of each element on either side of the equation

  5. Check that the correct state is indicated for each reactant and product


Combustion


  • Metal + oxygen —> metal oxide

  • Hydrocarbon + excess oxygen —> carbon dioxide + water


Decomposition reactions

  •  Reaction which one compound breaks into at least two products

  • Reactants decompose into parts

E.g. AB —> A + B


Combination (synthesis) reactions

  • Two or more simple form more complex products 

  • Reactants may be elements or compounds but the product is always a compound

E.g. A + B —> AB


  • To determine if a gas is carbon dioxide you can bubble the gas through lime water or place a lit splint into the gas

  • Exothermic reactions release heat

  • A chemical reaction has occurred when there is a change in colour, change of state (gas, solid, liquid), change in temperature etc.


Neutralisation

  • A reaction where an acid and a base react in an aqueous solution to produce salt and water

Acid + base —> salt + water


Ex.

Acid + active metal —> salt + hydrogen

Acid + metal carbonate —> salt + water + carbon dioxide


Key acids (must memorise)

  • Hydrochloric acid HCI

  • Nitric acid HNO3

  • Sluferic acid H2SO4


How to identify gas


Carbon dioxide 

  • bubble gas through lime water - turns cloudy

  • Put a lighted splint into a sample of the gas - extinguishes 


Hydrogen

  • Put a lighted splint into a sample of the gas - pop sound 


Oxygen

  • Put a glowing splint into a sample of the gas - relights


Precipitate

  • Solid that forms as a result of a chemical reaction in an aqueous solution

  • Only occurs if one product is insoluble


  1. Identify reactants

  2. Split reactants into positive and negative ions

  3. Possible products are found by swapping positive and negative ions in reactants

  4. Write and balance equation 

  5. Solubility rules to find if a product is insoluble

(one product soluble = reaction, both products soluble = no reaction)


Spectator ions

  • Ions that don't undergo a change 

  • No chemical change and on both sides of equation

  • All spectator ions should be removed from the equation


Formula for common molecules

Water: H₂O

Carbon dioxide: CO₂

Methane: CH₄

Oxygen: O₂

Hydrogen: H₂

Nitrogen: N₂

Carbon monoxide: CO


Metal displacement

  • A metal added to a solution with a less reactive metal and displaces the less reactive metal, becoming an elemental metal

  • More reactive metal forms ions in new solution


Chemical patterns


Protons

  • Located in the nucleus

  • Positive charge

  • Mass of 1


Neutron

  • Located in nucleus

  • Neutral charge

  • Mass of 1


electron

  • Located surrounding nucleus

  • Negative charge

  • Mass of 0.0005


Metalloids

  • Can behave both like metals and non metals


Neutrons: mass # - atomic #

Atomic #: protons

  • # of protons on an atom and determine place on the periodic table

Mass #: atomic # + # neutrons

  • Total number of protons and neutrons in an atoms nucleus


Electron configuration

  • Low energy electrons closer to nucleus and most stable

  • High energy electrons furthest fron nucleus and least stable

  • 4 shell pattern: 2,8,8,2

  • Elements in same group have same # of valence electrons

  • # valence electrons is # of units in the group # 


Energy of electrons

  • When an electron temporarily has an energy greater than it’s ground state, it occupies an excited state for a short period of time

  • They emit a photon with the same energy as the one absorbed when returning back to a ground state

  • Emission is observed as coloured light


Periodic table

  • Group number: how many valence electrons an atom has

  • Period number: how many electron shall an atom has

  • Group 18: noble gases

  • Transition metals is the middle part of the periodic table


Ions

  • Atoms with incomplete outer shells, making them unstable and reactive

  • When unstable atoms can gain or lose electrons to obtaon a full valence shell

  • Atoms that lose electrons are positive ions and are called cations

  • Atoms that gain electrons are negative ions and are called anions


Ions from metals

  • Metals lose electrons to match number of valence electrons of the nearest noble gas

  • positive ions form when the number of electrons is less than the number of protons

Ex.

Group 1 metals —> ion 1+

Group 2 metals —> ion 2+

Group 13 metals —> ion 3+


Ions from non metals

  • Gain electrons to match number of valence electrons of nearest noble gas

  • Negative ions form when the number of electrons is more than the number or protons

Ex.

Group 17 non metals —> ion 1+

Group 16 non metals —> ion 2+ 

Group 15 non metals —> ion 3+


Polyatomic ions (moecular ion)

  • Set of 2+ atoms that can behave as a 

          Single unit with a net charge thats not 0

(highlighted ions must be memorised)


Ionic bonding

  • Compounds that contain ions

  • Formed by a reaction between metals 

non metals

  • 1+ electrons are transferred from each

Metal to each non metal so they end up 

With full outer shells and are stable

  • Negative and positive ions are strongly

Attracted to eachother, the attraction is

Called ionic bond


Ionic lattice 

  • Oppositley charged ions arrange in a repeating pattern, alternation to form an ionic lattice

  • When an ionic substance melts the lattice is broken and is free to move around and can conduct electricity

  • Ionic compounds have high melting points because ionic bonds are strong and need lots of energy to be broken

  • Since water is a polar molecule (positive on one side and negative on the other) each side will stract the opposite charge of ions and break up the lattice (lattice dissolves in water)


Covalent bonding 

  • Only between non metals

  • Atoms try attain nobles gas structure by sharing electrons that are attracted by both nuclei - forming a covalent bond

  • Forms molecules (molecular compounds) 

  • No charged molecules (ions)

  • Attraction between molecules is weak so they have low melting and boiling points


Elements: pure substance composed on one type of atom

Compound: formed by 2+ different elements chemically bonded tgth

Molecules: formed by 2+ of the same atoms chemically bonded together


Isotopes: atoms of the same element with different number of neutrons but same number of protons

Malleability: ability of a metal to be molded/ deformed into a different shape

Ductility: ability for metal to be stretched