Chemical Analysis

Testing Ionic Compounds

• Ionic compounds are made up of

• Positive Ions (cations)

• Negative Ions (Anions)

• Tests are carried out to find specific ions

Flame Tests - Positive Metals Ions

• Lithium ions Li⁺ gives a crimson flame

• Sodium Ions Na⁺ gives a yellow flame

• Potassium ions K⁺ gives a lilac flame

• Calcium ions Ca²⁺give an orange-red flame

• Copper ions Cu²⁺ give a green flame

Steps for flame test

1. Clean a nichrome wire loop by dipping it in some HCL and the holding it in a blue flame from a bunsen burner until it burns without any colour

2. Dip the loop into sample and put back into the flame record the colour of the flame

3. Colours can be used to detect and identify different ions only works for samples that contain a single metal ion

4. If sample texted contains a mixture of metal ions multiple flame colours will be present hinding each other

Precipitation reactions - Positive Metal Ions

•  Calcium Ca²⁺ → White

• Copper(II) Cu²⁺ →  Blue

• Iron (II) Fe²⁺ → Green

• Iron (III) Fe³⁺ → Brown

• Aluminium Al³⁺ → White first,then redissolves in excess NaOH to form a colourless solution

• Magneisum Mg²⁺ → White

Positive Metal Ions - IONIC EQUATIONS

• Ca²⁺ 2OH^- →Ca(OH)₂

• format is (aq)+(aq) —> (s)

• Just put the metal and charge + (number of charge)OH^-

• plus element(OH)₂

Testing for carbonate ions - negative ions

• carbonate reacts with dilute acid you get salt water and carbon dioxide

• you can use co2 test for carbonate ions if you react a substance with an acid and it gives off a gas that turns limewater cloudy then the gas is c02 and the substance must contain carbonate ions

• acid and carbonate ions will produce co2 then it will go through the pipe and go into limewater which will make it cloudy

Testing for halide ions - negative ions (aq,aq = s)

• Chloride Cl^- - White - Ag⁺ +Cl^- → AgCl

• Bromide Br^- - Cream - Ag⁺ +Br^- → AgBr

• Iodide I^- - Yellow - Ag⁺ +l^- → AgI

• Important to use dilute nitric acid rather than HCL as chloride ions would be present meaning that a white percipitate will always be formed

Flame Emission Spectroscopy Steps/Expolkanation

• Sample placed in flame

• Ions heat up and their electrons become excited

• When electrons drop back to their original energy level they transfer energy as light

• light passes through a spectroscope which can detect different wavelengths of light to produce a line spectrum

• combination of wavelengths emitted by an ions depends on its charge and its electron arragment

• since no two ions have the same charge and same electron arrangement different ions emit different wavelengths of light

• so each ion has a different line spectrum

Flame Emission spectroscopy of mixtures

• it can be used to identify different ions in mixtures

• more useful than flame tests which only work for substances that contain a single metal ion

• it can also give quantitative results in numerical form

• intensity of spectrum indicates concentration of ion

Precipitate

a solid that forms and separates from a liquid solution due to a chemical reaction

Instrumental Methods

Methods that are accurate,sensitive rapid and can be automated 

Advtages of flame emission spectroscopy vs flame tests

• can detect multiple ions at once

• can determine the concentration of ions

• quantitative

• very sensitive

• very fast 

• very accurate

Disadvantages of flame emission spectroscopy vs flame tests

• expensive

• measurement errors

• destructive

• only identifies the presence of elements/ions doesnt identify compounds

• large machinery required

Chromatography

Analytical method used to seperate the substances in a mixture

2 Phases in Chromatography

• Mobile Phase - Molecules can move - this is a liquid or gas

• Stationary Phase - Molecules cant move - this is a solid or really thick liquid

Theory of Paper Chromatography

• Substaances in the sample constantly move between mobile and stationary phases

• Equilibrium formed between two phases

• Mobile phase moves through stationary phase and anything dissolved in MP moves with it

• The distribution of phases determines how quick the chemical moves

How do components separate?

• Seperates through stationary phase as long as components spend different amount of time in mobile phase

• No’ of spots formed change in different solvents

• Due to distribution of chemicals

• Pure substance will only ever form one spot in any solvent as long as there is one substance in sample

Time spent in each phase depends on

• How soluble they are in the solvent

• How attracted they are to the paper

• eg. higher solubility in solvent but less attracted to paper spends more time in mobile phase (further up)

Rf Value

• Result calleds chromatogram

• Is the ration between the distance travlled by the dissolved substance (baseline to centre of spot) and distance travelled by solvent

Rf Value Equation

Rf Value = distance travelled by substance (B)/ distance travlled by solvent (A)

Identifying substances using chromatography

• Often carried out to see if certain substance spresent in a mixture

• Pure sample of substance alongside unknown mixture

• Rf values of refrences and on of mixtures spots match substance may be present

• Rf values can change depending on solvent

Test for Chlorine

• Chlorine bleaches lamp litmus paper

• Turning it white may turn red at first

• Due to chlorine being acidic

Test for Oxygen

• Glowing splint inside test tube containing the gas

• If present it we relight the glowing splint

Test for Hydrogen

• Lit splint at open end of test tube containing hydrogen

• “squeaky pop”

Test for Carbon Dioxide

• limewater (solution of calcium hydroxide and water)

• Bubble gas through it

• Solution will turn cloudy if Co2 present

• Cloudiness formed by formation of calcium carbonate

Formulation

• manfucatured in chemical industry

• to transform raw active ingridients

• into safe,effective,stable,and usable final products for consumers across various sectors