what is chemical analysis?
● the process of determining the composition of a substance by identifying its parts
● has many impt applications in our society
○ analysis of drinking water
○ analysis of food
○ in the forensic investigation of crimes
● can be divided into 2 broad categories
○ qualitative analysis: to identify elements and compounds present in an
unknown substance (what is present)
○ quantitative analysis: to measure the concentration of elements and
compounds present (how much is present) (not the focus)
● in QA: we are interested in 2 things:
○ determine the name of a given unknown substance
○ determine the ions (cations & anions) that are present in a given unknown
substance
● QA is carried out using chemical reactions & chemical test reagents
● these reactions mostly involve observable changes including:
○ formation of a precipitate
○ evolution of a gas
○ colour change
in carrying out Qualitative Analysis
to determine the identity of an unknown substance, we can carry out:
● physical test/preliminary examination
○ colour
○ solubiliity
○ smell
○ pH
● chemical tests
○ tests for cations (NaOH & NH3)
○ tests for anions
○ tests for gases
■ precipitation
■ acid-base reaction
○ tests for oxidising & reducing agents
■ redox
● thermal decomposition (application for solid unknown only)
thermal decomposition
eg1: CuCO3 (s) [green]→ CuO (s) [black] + CO2 (g)
eg2: Zn(NO3)2 (s)→ 2ZnO (s) [yellow when hot, white when cold]+ 4NO2 (g) + O2 (g)
test for cations
● reagents used
○ aqeuous sodium hydorxide, NaOH
○ aqeuous ammonia, NH3
● how to add the reagents to an unknown solution
○ add a few drops
○ add in excess
● how to observe?
○ colour of ppt
how can we further differentitate Na+ and K+, since solutions containing