Water hardness, conductivity, and ions Flashcards
Water that contains excessive amounts of minerals can cause what in beverages?
Cloudiness
Hard water
Water the has a high mineral content, primarily calcium and magnesium
What do water softeners do?
Exchange sodium ions for the calcium and magnesium ions.
Analytical methods for minerals
Complexiometric titrations, precipitation titrations, colorimetric methods, ion selective methods, atomic absorption spectroscopy, inductively coupled plasma - atomic emission spectroscopy, ashing
EDTA complexiometric titration
Forms stable 1:1 complexes with mineral ions, stability of complex increases with valence of the mineral, complexation equilibrium is strongly pH dependent, with decreasing pH the chelation sites of EDTA become protonated. Calmagite and Eriochrome Black T (EBT) change from pink to blue when excess EDTA removes calcium and magnesium. pH must be 10 or more, but the ions precipitate at pH=12, so an ammonia buffer at pH=10 is used.
Conductivity
A measure of a substance’s ability to conduct and electrical current.
Conductivity can be measured by……
Applying an alternating electrical current to two electrodes immersed in a solution, and measuring the resulting voltage.
What is the SI unit of conductivity?
Siemens per meter and in standard it is mho per meter.
Precipitation titration
When at least one product if a titration is an insoluble precipitate.
Mohr Method
Estimation of salt concentration by directly titrating (forward titration) the chloride ions with silver nitrate. Bromide can also react with the silver nitrate and throw off the titration. The titration should be carried out at pH 6.5-9 because the accuracy of the end point is affected at low pH. The silver first reacts with the Cl and then with the chromate in potassium chromate to form an orange precipitate.
Volhard method
A back titration used for the estimation of salt. Chlorieds are first precipitated with excess silver nitrate, and the excess silver is titrated with potassium or sodium thiocyanate. The end point is when the thiocyanate reacts with available iron cations to produce a red colored complex.
Mohr Method
Estimation of salt concentration by directly titrating (forward titration) the chloride ions with silver nitrate. Bromide can also react with the silver nitrate and throw off the titration. The titration should be carried out at pH 6.5-9 because the accuracy of the end point is affected at low pH. The silver first reacts with the Cl and then with the chromate in potassium chromate to form an orange precipitate.
Volhard method
A back titration used for the estimation of salt. Chlorieds are first precipitated with excess silver nitrate, and the excess silver is titrated with potassium or sodium thiocyanate. The end point is when the thiocyanate reacts with available iron cations to produce a red colored complex.
When do you use the Mohr method and when do you use the Volhard method
Mohr is used when the solution is neutral or basic, Volhard is used when it is acidic.
Chloride analyzer
Determination of chlorides by argentimetry. Silver ions are generated by passing a constant current between two silver electrodes. The end point is detected when excess silver ions cause a change in soltion conductivity which is detected by sensing electrodes.
