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ncea level1 chemistry exam summary sheet with definitions, example questions, answers, etc.

Decomp­osition Reactions

Metal Carbonates
when metal carbonates decompose they form a metal oxide and carbon dioxide gas.
eg. when solid green copper carbonate is heated, a black solid and a colourless gas is formed. The gas turns limewater cloudy when bubbled through it.
copper carbonate --> copper oxide + carbon dioxide
an exception of this rule is silver carbonate, which decomposes to form silver metal, carbon dioxide, and oxygen.
Metal Hydroxides
when metal hydroxides decompose they form a metal oxide and water.
eg. when solid white calcium hydroxide is heated, a white solid and a colourless liquid is formed. The liquid turns blue cobolt chloride paper pink.
calcium hydroxide --> calcium oxide + water
Metal Hydrogen Carbonates (bicar­bon­ates)
when metal hydrogen carbonates decompose they form a metal carbonate, carbon dioxide, and water.
eg. sodium bicarb­onate --> sodium carbonate + carbon dioxide + water
Catalytic Decomp­osition
a catalyst reduces the amount of energy needed for a reaction to proceed. They allow reactions to take place at room temper­ature that would otherwise require higher temper­atures.
Hydrogen peroxide: the decomp­osition can be sped up by the catalyst manganese dioxide (MnO₂).

Combin­ati­on/­Syn­thesis Reactions

Chemical reactions where the atoms of one element react with the atoms of another element to form a single compound.
element A + element B --> element AB
Combin­ation Reactions with Oxygen
-sometimes called oxidation reactions
-when heat/light is produced it is also known as combus­tio­n/b­urning
-the product is more stable than the reactants
-can have a unique flame colour (see important observ­ations)
Ionic Compounds
when metal elements combine with non-metal elements.
-valence electrons are transf­erred from the metal to the non-metal
-the metal forms a positive ion and the non-metal forms a negative ion
-the ions are held together by electr­ostatic forces of attraction (posit­ive­-ne­gative)
Covalent Compounds
when non-metals combine with other non-me­tals.
-bonding electrons are shared so that each atom has a stable full valence electron shell


positive charge, large mass, in the atom nucleus, top left number
neutral charge, large mass, in the atom nucleus, subtract the number of protons from the bottom right number
negative charge, very tiny mass, in the outer shells, top left number
negatively charged ion
positively charged ion
The number of protons deciphers the atom. The number of neutrons can change to create isotropes.
When forming equations, always put the cation first eg. Na + Cl --> NaCl not ClNa

Chemical Reactions

'During a chemical reaction matter cannot be created nor destro­yed.'
This is the law of conser­vation of mass.
This means that the reactants and products shown in a chemical equation must balance.
Eg. 4Fe +3O₂--­>2Fe₂O₃
In this equation, the 4 is a coeffi­cient. These are whole numbers that multiply the following atom/m­ole­cule.
In this equation, the 2 is a subscript. These are whole numbers that represent the number of atoms/­mol­ecules immedi­ately proceeding it.

Precip­itation Reactions

soluble means dissol­vable
-some ionic salts will readily dissolve in water- these are soluble
-when they dissolve the ions dissociate (break apart into their + and - ions)
-other ionic salts will only sparingly dissolve in water- these are considered insoluble
AB + CD --> AD + BC
-a precip­itate will only form if one of the products formed is insoluble
-you will observe the solution becoming cloudy and typically white solids will form
eg. lead nitrate + sodium carbonate --> lead carbonate + sodium nitrate
colourless solution of lead nitrate mixed with colourless solution of sodium carbonate forms white precip­itate of lead carbonate in a colourless solution of sodium nitrate.
two soluble solutions were mixed together which allowed ions to exchange, forming the insoluble lead carbon­ation as a precip­itate.
lead carbonate is insoluble because lead ions and carbonate ions are more attracted to each other than they are to water.

Important Observ­ations

silvery grey except copper which is pinky orange. Copper metal formed in a displa­cement reaction is reddy-­brown.
oxygen, hydrogen, and carbon dioxide are all colour­less.
white solids except copper carbonate which is a green solid and silver carbonate which is a yellow solid.
white solids except iron (II) hydroxide which is a green solid, iron (III) hydroxide which is an orange/red solid, and copper hydroxide which is a blue solid.
Hydrogen peroxide is a colourless liquid.
Manganese dioxide is a black solid which catalyses the decomp­osition of hydrogen peroxide into water and oxygen gas.
Combin­ation Reaction Observ­ations
Magnesium burns with a bright light to form a grey-white ash of MgO.
Sulfur; yellow non-metal- burns with a blue flame to form a colourless gas with a suffoc­ating, choking odour, SO₂.
Carbon; black non-metal- burns with a yellowy flame to make a colourless gas CO₂.
Iron + Sulfur react when heated- glows and forms a black non-ma­gnetic solid of FeS.
Hydrogen; colourless gas + O₂ will explode with a small flame. After heating the solid glows a red-hot and a black solid is formed.
Tests for Products Observ­ations
gas burns with a squeaky pop
Carbon Dioxide
gas turns colourless limewater cloudy­/milky
gas relights a glowing splint
turns blue cobolt chloride paper pink

Displa­cement Reactions

when a single atom 'displ­aces' another metal ion from within a compound.
More reactive metals on the activity series replace a less reactive metal ion from the compound. Ag is the least reactive metal.
metal A +compound BC --> compound AC +element B
eg. Mg+FeS­O₄-­->F­e+MgSO₄ because magnesium is more reactive than iron
To form an ionic equation, we get rid of the negative ion (spectator ion) because it is not involved in the reaction.
eg. to form Mg + Fe2+ --> Fe + Mg2+*
*the 2+ is written as a little number top right of the element.


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