The freezing point of an aqueous saturated
solution of I, is -0.0024°C. More than this
can dissolve in a KI solution because of the
following equilibrium 12(09) + ling) 15/09)
0.1 M KI solution dissolves 12.5 g/L of l..
Calculate the equilibrium constant K for the
above equilibrium. Also calculate the
freezing point of the resulting solution.
Assume molarity to be equal to molality and
also assume that conc. ofl in all saturated Solutions is same.
[K for water=1.86 K kg mol']
Answers
Answer:
Dissolved organic matter (DOM) is found in all freshwaters globally, by dissolving in
rainwaterduring its path through soil and on to oceans via. rivers and streams. To provide
potable water fit for human consumption, selected streams and rivers are used by either direct
abstraction, or by diversion into reservoirs prior to treatment. For ca.100 years, chlorine and
its compounds have been used by water treatment companies to disinfect water. However,
research has shown that reactions between chlorine and DOM can produce compounds
(disinfection by-products, or DBPs) which may be hazardous to human health. This thesis
explores the relationship between catchment character, organic matter concentration, and the
potential formation of DBPs. In particular, trihalomethanes (THMs) were measured as these
are currently the only regulated DBPs in the UK. To achieve this, water samples were
collected quarterly over one year from two contrasting catchments, to study seasonal
variations in DOM concentration and character. A third catchment was also sampled, with
similar catchment characters to the first two catchments, to determine whether geographical
location and land use types affected the data.
Each catchment was studied to see if catchment characteristics (e.g. class of vegetation, soil
type or bedrock) could be mapped using a Geographical Information Systems (GIS)
approach), to observe any effects on DOM and/or the DBPs found in treated water, with the
aim of producing a risk assessment map to aid the choice of future abstraction locations for
drinking water. Hence, samples were chlorinated and chloraminatedin the laboratory before
being analysed for DBP formation and residual chlorine concentrations were measured.
Catchment specific GIS derived data were statistically analysed with water chemistry data,
and detected relationships were explored statistically.
Major findings include medium to strong positive correlations between the standardised
THM4 (STHM4 – the concentration of THM4 formed from 1 mg L-1
dissolved organic
carbon (DOC)) concentration and geology, where an increase of the area of inland rock in a
catchment increases STHM4 concentration. Medium strength positive correlations were
found between STHM4 and vegetation classes, where, as the area of acid grassland, and
heather increase, so does the concentration of STHM4. Negative relationships were
discovered showing the obverse, where, as loamy and clayey floodplain soils with naturally
high groundwater increased in area, STHM4 concentration dropped (at the Hampshire Avonand Conwy catchments combined). The occurrence of coniferous woodland in a catchment
was found to correlate with the CHCl3 formation potential of waters (Pearsons, f=0.530,
p=<0.05, n=20), supporting findings in published literature.
Laboratory based chlorination and chloramination of sample waters, followed by gas
chromatography provided DBP data, specifically THM4. These data show that more
chloroform was formed after chlorination than chloramination, and that chloramination
formed 3 times more CHBr3 (another THM4 compound) than chlorination, under laboratory
formation potential conditions. Results showed that the chlorination of water prior to DOM
removal could result in a THM4 concentrations 5 times greater than the current UK
regulatory limit, per mg L-1 dissolved organic carbon (DOC), whereas chloramination forms
ca.5 times less than the current UK regulation per 1 mg L-1 DOC. However, chlorination of
water prior to DOM removal is never done in practice, so this data provides information on
the composition of the organic matter and whether DOM from a specific catchment contains