C8 Chemical Analysis

Purity

contains only one compound or element

How does the boiling/ melting point tell you how pure a substance is?

pure substance will boil/melt at a specific temperature

test by measuring bpt and comparing to boiling point of the substance form a data book

closer the value is to the actual value the more purer the substance

impurities will lower the melting point/ increase bpt and increase the melting range

Formulations

useful mixture of compound and substances that do not react together

produce a useful and desirable characteristics or properties to suit a particular function

medicine- altering the formulation ensures the drug is delivered to the correct part of body at the right concentration

Chromatography

method used to separate mixtures of soluble substances and to identify substances

Mobile Phase

Stationary Phase

where the molecules can move - liquid or gas - solvent (water)

where the molecules cant move- solid or thick liquid chromatography

During Chromatography the substances in the sample ..

The ____ moves through the …

constantly move between mobile and stationary phase to form an equilibrium between the two phases

mobile phase 

stationary phase and anything dissolved in the mobile phase moves with it

What determines how quickly a chemical moves in chromatography?

how it’s distributed  between the phases - more time in the mobile phase than stationary phase will move further.

Chromatography

where do components normally separate ?

stationary phase

Why might the number of spots change?

different solvents because the distribution of the chemicals will change

pure substance only 1 spot because only one substance

why does the time each molecule spends in each phase depend on?

how soluble they are in the solvent

how attracted to the paper they are

molecules with higher solubility and less attracted to paper will spend more time in mobile phase - further up the paper.

rf value

distance travelled by substance (Baseline to centre of spot) / distance travelled by solvent

Why is chromatography carried out?

to see if a certain substance is present in a mixture

run a pure sample of that substance alongside the unknown mixture . If rf values of the reference and one of the spots in the mixture match the substance may be present

rf value is dependent on the solvent . If the solvent changes so will the rf value 

Chromotography required practical

1. draw a pencil line across the chromatography paper, 1 - 2 cm from the bottom

2. use a pipette to add small spots of each ink to the line on the paper

3. place the paper into a container with a suitable solvent in the bottom

4. allow the solvent to move through the paper, but remove the chromatogram before it reaches the top

5. allow the chromatogram to dry, then measure the distance travelled by each spot and by the solvent

6. Calculate R_f value

chlorine

bleaches damp litmus paper turning it white 

oxygen

glowing splint relights

Carbon Dioxide

Bubbling Co2 through limewater causes solution to turn cloudy

Hydorgen

lit splint at the open end of a test tube containing hydrogen creates a squeaky pop sound

(hydrogen burning quickly with oxygen)

Carbonates

test

substance containing CO_3^2- ions

add acid then connect to lime water

Test sulfate ions

add hydrochloric acid and 2 drops of Barium chloride solution if present a white precipitate will form

Test Halides

add nitric acid and silver nitrate solution

chloride - white precipitate

bromide - cream precipitate

iodide - yellow precipitate

Flame tests

Lithium ions

Sodium Ions

Potassium ions

calcium ions

Copper ions

crimson yellow lilac orange-red green 

Flame test

clean wire loop and dip into a sample of solid compound being tested

Place loop into flame of Bunsen burner set to roaring blue flame

observe colour and record in a table

only works for sample with 1 metal ion

if multiple some colours blocked by the colours of other ions.

metal hydroxides

insoluble and precipitate out of a solution when formed

metal hydroxide test

add a few drops of sodium hydroxide solution to solution

Calcium green

copper blue

iron green 

iron 3 brown

aluminium white then redissolves to form a colourless solution

Magnesium white

Metal hydroxide ionic equation

only show ions involved in precipitation reaction

do not show sodium or sulfate ions (spectator)

Cu²⁺ + 2OH^- → Cu(OH)₂

Fe_³⁺ + 3OH^{- →} Fe(OH)₃

flame emission spectroscopy

instrumental method of analysis - identify ions an their concentration.

sample placed in a flame.

As ions heat up their electrons become excited and move to a higher energy level.

When the electrons drop back to their original energy level they transfer energy as light which passes through a spectroscope which can detect wavelengths of light to produce a line spectrum

To identify the metal present the spectrum is compared with reference spectra from known metal ions 

what does the combination of wavelengths depend on?

ion charge and electron arrangement

since no 2 ions have the same charge and electron arrangement different ions emit different wavelengths of light so each ion produces a different pattern of wavelengths and different line spectrum.

What does the intensity of the spectrum indicate

concentration of that ion

Why is flame emission spectroscopy more useful than flame tests?

identify different ions in mixtures

flame tests only work for substances containing a single metal ion

Advantages of using a machine

verry sensitive can detect smallest amounts of substances

very fast and tests can be automated

verry accurate