chemical analysis

pure susbtance

a single element or compound not mixed with any other substance

mixture ( a substance that contains 2 or more different substances that aren’t joined together)

element ( one type of atom)

compound (2 or more types of atoms chemically bonded 4

pure elements and compounds melt at specif temps

• measure the melting point

• pure substances have a sharp melting substances

• and impure melt over a broader range of temperatures

formulations

a mixture designed as a useful product (paint, medicine, makeup, alloys, NPK fetilliser)

mix together components that have a particular purpose in carefully measured quantaties to make sure the product has the desired characteristics

impure substacnes

lowers melting point

and raises the BP

The more impurity the greater the difference in MP and BP

in liquids, an impurity dillutes the conc of a liquid, decreasing the number of molecules that can vaporise at any given temp

decreasng vol increases the pressure as a higher temp required to get enough molecules to vaporise to allow boiling to occur

impurities in a solid disrupt the repeating pattern of forces that holds a solid togethere, smaller amounts of energy is requird to melt the part of the solid surrounding the impurity so the melting point isn’t as high

chromatogrpahy

method used to separate mixtures

also useful in indentifying certain substances

chromotogprahy paper

pencil line

dyes across the line

placed into solvent

solute- what dissolves

solvent- does the dissolving

solubility- how easy it dissolves

2 phases of chromatogrpahy

mobilephase- the solvent that carries the different substances

stationary- non moving phase ( the paper _

RF VALUE to identify unknown val

measure distance moved by substances / distance moved my solvent

both measured from pencil line (one to dye) and (one to the paper)

value always between 0 and 1

mixtures separate into different spots depending on the solvent , but pure compounds produce a single spot

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

2. use a pipette or capillary tube 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

hydrogen test oxygen

lit splint at neck of test tube containing gas, presence of hydrogen is a squeaky pop sound

glowing spliint, 02 presence the splint re lits

carbon, buble gas through aq solution of lime water, if present lime water turns cloudy

chlorine, damp blue litmus paper onto gas, if bleached turns white

flame tests

identifies some metal ions

dip nichrome wire into hcl (nichrome is unreactive

heat the wire in a blue bunsen flame until it ives no colour (reomve contaminant metal ions)

dip wire into water

dip wet wire into substance being dissolved

put into blue bunsen flame (note colour)

lithium - crimson

na- yellow

potassium - lilac

calcium- orange-red

copper- green

when metal compounds heated electrons in metal ions absorb energy

electrons promoted to higher energy level

electrons drop back to their ground state and release excess energy but as light and not heat

different amounts of energy released produces different colours of light

identifying metal ions

mixture of different ions, and the flame colours can be masked because of the different colours being mixed together (problems in flame test)

metal hydroxide tests

add sodium hydroxide to solution

observe the colour of the precipitate that forms

aluminium- white

calcium- white

magnesium- white

copper- blue

iron 2 - green

iron 3 - brown

the 3 that form white, add more sodium hydroxide so its excess, only aluminium dissolves again, and calcium and magnesium dont

carbonate ions

react carbonates with dilute acid, forming co2 gas

now bubble the gas through limewater

if present limewwater turns cloudt

halide ions

add nitric acid and silver nitrate to the solution (nitric because hcl has chloride ions in it)

precipitates

silver chloride - white

silver bromide - cream

silver iodide- yellow

remeber trend of colours

testing sulfate ions

barium chloride solution and dilute hcl

white precip forms

baso4

insturmenta methods

-more accurate than flame tests

-more sensitive

-rapid tests

Flame emission spectroscopy analyses metal ions in solutions

-expensive

-special training to use them

sample put into flame

light passed through spectroscope

spectroscope gives a line spectrum thats analaysed to identify the metal ions in the solution

the concentration of the metal ions in the solution can also be found