Chemistry Salters B Elements of the Sea

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  • Created on: 12-04-13 11:10

Halogen

Benefits

Risks

Fluorine

Used to make plastics such as PTFE
Applied to toothpaste to strengthen tooth paste enamel
Used to make HCFC

Element is highly reactive and handling must be kept to a minimum.

Chlorine

An important intermediate in the manufacture of hyrdochloric acid and chlorinated solvents.
Used in the plastics industry (for PVC and polyurethanes)
Used in water treatments and to make pesticides, medicines and bleach.

Pesticides can accumulate in the environment (e.g. DDT)
CFCs destroy stratospheric ozone.

Bromine

Used in the manufacture of flame retardants, agricultural fumigants and in photography.

Organic Bromine compounds can destroy ozone in the stratosphere.

Iodine

Used in antiseptics, germicides and dyes.
Iodine 131 is used to detect thyroid disease.

Ions in Solid and solutions

Chem Ideas 5.1
Ionic equations
Ions in solution behave independently – and this includes when they are involved in chemical reactions.If two solutions react to form a solid, a precipitation reaction is said to have occurred.
Spectator ions do not take part in the reaction so are not included in the ionic equation.
These rules will help you to predict whether and ionic precipitation reaction will take place when two solutions are mixed.
All nitrates are soluble in water
all chlorides are soluble in water except AgCl and PbCl2
all sulfates are soluble in water except BaSO4, PbSO4 and SrSO4.
All sodium, potassium and ammonium salts are soluble in water.
All carbonates are insoluble in water except (NH4)2CO3 and those of group one.
Neutralisation reactions can also be summarised using ionic equations. When an acid and alkali reacts with sodium hydroxide the ions involvedand the products are:
H+(aq)+Cl-(aq)+Na+(aq)+OH-(aq) ->H2O(l)+Na+(aq) + Cl-(aq)
Ionic equation: H+(aq)+OH-(aq)->H2O(l).
Calculations of concentrations
Concentrations can be measured in grams per cubic decimetre (gdm-3)
Using concentrations in calculations

a titration is a method of quantitively finding the concentration of a solution by reacting a known volume of it with another solution of a known concentration. The end point of a reaction is often detected by the use of an indicator that changes colour.

·         A fixed volume of solution of unknown concentration is placed in a conical flask using a pipette.

·         A few drops of a suitable indicator are added to the mixture and placed on a white tile (to see the end point clearly).

·         The solution of known concentration is added slowly from a burette with constant swirling.

·         As you approach the end point, add the solution from a burette drop wise.

·         After a rough titration, accurate titrations follow until concordant results are gained.
Atoms and Ions
First Ionisation enthalpy
First ionisation enthalpy is the energy needed to remove one electron from each of one mole of isolated gaseous atoms of an element.One mole of gaseous ions with one positive charge is formed. Units are kJmol-1
X (g) ->X+ (g) +e-
The value of the 1st ionisation enthalpy is always positive – energy must be put in to remove the electron because it is…

Comments

Eleanor Rawsthorne

WOW! just came on here to look at the halogen risks and uses and this was the first thing I found :) absolute star, thanks :)

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