Cape Chemistry Reminders

Relative Atomic Mass

Relative Atomic Mass

This is the average mass of an atom of an element according to 1/12 of the mass of carbon-12

Ionic Bonding

This is the electrostatic attraction between two oppositely charged atoms forming a lattice. This usually involves the attraction between a metal and non-metal

Covalent bonding

This is force of attraction between the nuclei of two neighboring atoms and a pair of electrons between them.

Metallic Bonding

This is the sharing of free electrons among the lattice of positively charged metal ions.

Law of Conservation of Mass

states that masses cannot be created or destroyed. This means that the combined masses of the product of the reaction is equal amounts to the combined masses of the starting reactants.

Law of Definite Proportions

states that different samples of a pure substance will contain the same proportions of the same element by mass.

Mole

This is the amount of substance which has the same number of particles as there atom in exactly 12g of carbon-12 isotope.

Empirical Formula

This is the simplest formula showing the relative amount of atoms in a compound. It is the simplest of a mole ratio of elements in a compound

Molecular formula

It tells the actual number of atoms of element a molecule present in a compound. This only for molecular substances. It is a simple whole number multiple of the empirical formula

Avagadro’s Law

states that at the same volume all gases of the same pressure and temperature has equal number of molecules.

R.T.P.

1 mole= 24

S.T.P.

1 mole = 22.4

Concentration of a solution

refers to the amount of solute dissolved in a specific solvent to create a solution.

An electron is stable when…..

its wavelength or multiple of it, is exactly fit around a nucleus at a particular distance

Titration

This is a method of analysis that allows you to determine the precise endpoint of a reaction and therefore the precise quantity of reactants in the titration flask.

A burette is used for…..

deliver the second reactant to the flask

An indicator or pH meter is used to…

detect the endpoint of a reaction.

The standard solution of a titrant

is a solution of known concentration that is required to react quantitatively with another solution of unknown concentration.

Primary standard

this is a substance of high purity used to prepare the concentration of the standard solution in the volumetric analysis.

Properties of primary standard

high purity, stable towards air, absence of water of crystallization, high formula weight, soluble in titration medium

Why cant sodium hydroxide be a primary standard?

This is because it is impure, hydroscopic, absorbs oxygen in air. It also absorbs moisture in air

Preparing a Standard Solution by Dilution

Fill clean dry burette with more concentrated solution.

Run calculated volume of the more concentrated solution in the volumetric flask

Make solution up to the mark with distilled water. Invert several times

Equivalence Point

This is when both solutions are the same number of moles.

Endpoint

This is when there is a color change and it signals that the reaction is complete.

Use of Titration

to determine the amount of substance in an unknown solution

Determining concentration of solution of alkali

1. Fill the burette with the acid known concentration (after washing with acid).

2. Record initial reading

3. Put a known volume of the alkali into a flask using a pipette

4. Add an acid-base indicator into the flask with the alkali

5. Add slowly the acid from the burette until the indicator color change (endpoint)

Heat of fusion

This is the amount of energy required to change one gram of a solid to a liquid without changing its temperature.

Vapor pressure is called Saturated vapor pressure when

the molecules reach a dynamic equilibrium for this is when the rate of evaporation is equal to the rate of condensation

When does a liquid boils

This is when the saturate vapor pressure is equal to external pressure hence called vaporization.

Boyle’s Law

The volume of a fixed mass of gas is inversely proportional to pressure at constant temperature. P= k/V

Charles Law

The volume of fixed mass of gas is directly proportional to the absolute temperature at constant pressure.

Absolute Zero

This is the temperature at which the volume of the gas becomes zero if it did not condense.

Constant Volume Law

The the pressure of a fixed mass of gas is directly proportional to temperature at constant volume

Ideal Gas

This is a gas which obeys the general gas equation of PV=nRT and other gas laws at all temperature and pressure

When do real gases approach ideal gas behaviour

In high temperatures and low pressure

When do real gases