QUANTITATIVE ANALYSIS Determining amount of ions present in samples

Gravimetric analysis 1.63 g fertiliser is added to mL water. Excess BaCl 2 is added until no further ppt forms After filtering and drying to constant mass, sample weighed 1.81 g Calculate percent sulphate Describe how the reliability and accuracy of the procedure could be improved. Calculate percent sulphur

Gravimetric Analysis Find the % Mg ions in 250 mL sea water Done by adding excess NaOH to form g of ppt

HSC Question: Evaluate the use of gravimetric analysis in determining the chemical composition of materials such as lawn fertilisers.

Instrumental Analysis

Cathode lamp

AAS Cathode lamp is specific for the element to be measured Eg. To test lead in water sample use a lead cathode; the lamp will generate wavelengths that are specific to lead Absorbance (A) α Concentration (c) Standard Solutions Prepare a series of dilutions of a standard solution containing the metal to be analysed Nebuliser The diluted standards and unknown are aspirated into the flame; light is absorbed by the hot atoms

Measuring Absorption The light passes through a monochromator (mirrors & diffraction grating) which selects a single wavelength The intensity of this selected beam is measured It is compared to the reference beam (with no sample) and converted into an electrical signal A = kc The greater the concentration, the greater the amount of light absorbed.

Calibration graph A control blank (containing only solvent) is used; zero concentration = zero absorbance

HSC Question: Assess the impact of AAS on the scientific understanding of the effects of trace elements.