Chapter 15: Analysing Water for Salts Flashcards
What is qualitative analysis?
Qualitative analysis is the process of finding what substances are present in a sample.
What is quantitative analysis?
Quantitative analysis is the process of measuring the quantity of a substance in a sample.
What is the most common salt found in water?
Sodium chloride, NaCl.
What causes hardness in water? What is a major cause of hardness?
Hardness makes water difficult to lather, and unsuitable for use in boilers and high-temperature applications.
Dissolved calcium and magnesium ions in water cause hardness.
What is a contaminant?
A contaminant is an unwanted substance that makes water unsuitable for an intended use.
Explain four ways contaminants enter water.
Direct discharge from factories and other sources.
Stormwater run-off: Water flows over the surface, coming into contact with contaminated soil, dissolving soluble components.
Contaminated air contact: Components of contaminated air dissolve or react with water.
Contaminated ground water contact
What are organometallic contaminants? Give an example.
Organometallic compounds are formed when organic molecules react with some heavy metals. These can be environmentally dangerous.
An example of one of these compounds is methyl mercury, a toxic compound that was being released into the water by a chemical company in Japan back in 1956.
Why is it necessary to have strict protocols for the collection of water samples?
These protocols exist in order to produce accurate analytical results. They are applied before, during, and after sampling takes place.
What is the electrical conductivity analytical method?
Measured in EC units, electrical conductivity is a quick and cheap method that measures the overall salt content of a water sample.
What is colorimetric analysis?
Colorimetric analysis is a technique in which colour levels are compared with a set of standards; the intensity of the colour depends on the component being analysed.
How does an instrumental colorimeter work?
It compares the colour in the test sample with colours produced in samples of known concentrations that have been treated identically.
It involves shining light of a complementary colour through the solution and measuring the amount absorbed.
From the readings produced, a graph of absorbance versus concentration may be produced and the sample with the unknown concentration may be determined.
Why is light of a complementary colour used in an instrumental colorimeter?
Light of a complementary colour to the test cell is used to obtain more accurate results.
How is UV-visible spectroscopy different to colorimetry?
UV-visible spectroscopy measures the absorption of light at a particular frequency. It is far more selective and less likely to suffer interference from similarly coloured compounds.
How does atomic absorption spectroscopy work?
In AAS,
