What a Blast: Outcome 3

Neutralisation

a chemical reaction that happens when an acid and alkali mix together, forming a new substance

Neutralisation equation:

acid + base/alkali -> salt + water

Naming salts

The name of the salt contains 2 parts, derives partly from the acid & alkali

Naming salts example:

Sodium hydroxide (NaOH-) + hydrochloric acid (HCl+)

Sodium chloride (NaCl) + Water (H2O)

Acids with carbonates

Rocks that contain carbonates (limestone, calcium carbonates) react with acid in a predictable way, limestone is eroded

Evidence of reaction: acids with carbonates

If an acid is mixed with a metal carbonate, fizzing is seen. Fozzing is caused by bubbles of a gas made during the reaction.

What gas is produced when a metal carbonate reacts with an acid?

Carbon dioxide

How can we test if a rock contains a metal carbonate?

Carbon dioxide gas turns limewater cloudy.

If the gas produced during a reaction between an acid and a metal carbonate is bubbled into lime water, the limewater turns cloudy

Metal carbonates reacting with acid equation:

Acid + Metal carbonate -> Salt + Water + Carbon dioxide

Acids reacting with carbonates example:

Hydrochloric acid (HCl) + calcium carbonate (CaCO3)

Calcium chloride (CaCl) + Water (H2O) + Carbon dioxide (CO2)

Is there a change in mass when carbonates react with acids?

Yes! When an acid and a metal carbonate react in an open container, the carbon dioxide produced escapes into the air, and the mass in the container decreases.

This change in mass can be shown graphically.

Corrosion

General corrosion occurs when most or all of the atoms on the same metal surface are oxidized, damaging the entire surface. Most metals are easily oxidized: they tend to lose electrons to oxygen (and other substances) in the air or in water.

Do all metals corrode?

Metals behave differently when exposed to the environment.

For example, gold is an unreactive metal and does not corrode easily. On the other hand, Zinc is a fairly reactive mental and corrodes easily.

Despite being a very reactive metal, why doesn't aluminium corrode?

The outer aluminium atoms react with the atmosphere. This forms a thin layer of aluminium oxide on the metal's surface which protects the metal from corrosion.

What is rusting?

Rusting is the specific name given to the corrosion of iron. Rusting is a chemical reaction between iron, oxygen and water, and it's chemical name is hydrated iron oxide.

What can speed up the process of rusting and why?

Salt can speed up the process of rusting because it acts as an electrolyte (a material containing free ions that allows it to conduct electricity), causing iron to lose electrons more quickly and therefore speeding up the rusting process.

Combustion Reaction

A combustion reaction occurs when an element or a compound reacts with oxygen, often producing energy in the form of heat

What is needed for a combustion?

- Hydrogen

- Carbon

- Oxygen

- A hydrocarbon such as methane, propane, butane and octane

Combustion facts

- Combustion reaction involves oxidation and reduction

- Before a substance will burn, it must be heated to its ignition point or kindling temperature.

- Combustion reactions mostly have to do with burning and heating

Acid with metals reaction

Many metals react with acids to form a salt and hydrogen gas.

The salt will depend upon the metal and acid used:

- Hydrochloric acids metal chloride

- Sulphuric acid gives metal sulphate

- Nitric acid gives metal nitrate

Acid with metals equation

Metal + Acid -> Salt + Hydrogen gas

Evidence of reaction: metals with acid

some of these reactions show bubbles (hydrogen gas) being produced

Example, solve for metals with acids reaction:

Magnesium (Mg) + Sulphuric acid (H₂SO₄)=

Magnesium sulphate (MgSO₄) + Hydrogen gas (H2)

How can we predict how vigorous a metals with acids reaction will be?

We can use the activity of the metals to predict how vigorously a metal will react.

The more reactive the metal, the more vigorous the reaction. The least reactive metals do not react at all.

How do you write formula equations?

1. Write down the word equations

2. Replace words with the chemical formula (You will be given or need to look up the formula at this stage)

3. Check that they are equal numbers of each type of atom on both sides of the equation, if not then balance the equation by using more than one

Example: Magnesium + Hydrochloric acid -> Magnesium chloride + Hydrogen gas

Mg + HCl -> MgCl2 + H2

Precipitation Reactions

Forms an insoluble salt when two soluble salts combine.

The resulting solution is visibly cloudy due to the formation of small aggregation of the insoluble salt. This insoluble salt falls out of the solution and is unfiltered to form the precipitate.

This reaction is a double-replacement reaction

Soluble

Ionic compound dissociates in solution.

Symbol (aq)

Insoluble

Does note dissociate in solution, aka a precipitate

Symbol (s)

General precipitate reaction equation

AB + CD -> AD + CB

How can we predict precipitation reactions?

Solubility rule -> if an ion is soluble, then it remains in its aqueous ion form.

If an ion is insoluble, it forms a solid with an ion from the other reactant.

If all ions in a reaction are shown to be soluble, then no precipitation reaction occurs.

Balancing precipitation reactions

Precipitation reaction can be balanced by ensuring that an equal number of atoms are present on both sides of the equations.

Examples of precipitation reactions in real life are:

- precipitation in water pipes

- formation of kidney stones

- formation of the immune complex

Decomposition reaction

A chemical reaction in which a compound breaks down into two or more products.

The products may be any combination of elements and compound - but the reactants are compounds

General equation for the decomposition reaction is:

AB -> A + B

Example:

H2O can be broken down into...

H2O = H2 + O