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 |
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Definitions
Protons |
positive charge, large mass, in the atom nucleus, top left number |
Neutrons |
neutral charge, large mass, in the atom nucleus, subtract the number of protons from the bottom right number |
Electrons |
negative charge, very tiny mass, in the outer shells, top left number |
Anion |
negatively charged ion |
Cation |
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. |
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Important Observations
Metals |
silvery grey except copper which is pinky orange. Copper metal formed in a displacement reaction is reddy-brown. |
Gas |
oxygen, hydrogen, and carbon dioxide are all colourless. |
Carbonates |
white solids except copper carbonate which is a green solid and silver carbonate which is a yellow solid. |
Hydroxides |
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 |
Hydrogen |
gas burns with a squeaky pop |
Carbon Dioxide |
gas turns colourless limewater cloudy/milky |
Oxygen |
gas relights a glowing splint |
Water |
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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