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Chemistry 113 Lab 10
Terms in this set (11)
Example of a sedimentary rock containing Ca²⁺
Limestone (CaCo₃), dolomite (CaMg(CO₃)₂) and gypsum (CaSO₄∙2H₂O)
What is meant by the hardness of water
Water that contains a large combined concentration of Ca²⁺ and Mg²⁺
Why scale formation is the bane of industry
It narrows pipes, blocks jets and tubes, and evaporator surfaces. The hard layer interferes with heat transfer in boilers, leading to gross energy inefficiencies and can lead to metal corrosion and structural weakness. The harder the water, the greater the problem.
A common method of softening water
Evaporating the solvent (water) and examining the residue of the nonvolatile solids that remains (total dissolved solids)
Why some salad dressings contain EDTA-chelated calcium
- Used as a preservative
- The calcium chelate removes any trace iron or copper ions that promote the spoilage of the oil
The difference between "Total Dissolved Solids" analysis and "Divalent Cation Analysis"
The divalent cation concentration of water is often referred to as the hardness of water. TDS is related to hardness but is not identical to the hardness of a sample. For example, a water sample with a high TDS would be considered "hard" water.
What happens when a hard water sample is treated with a "cation exchange resin"? Why would you want to do this?
When a hard water is treated with cation exchange resin, calcium, manganese, iron and magnesium ions are exchanged for sodium or potassium ions. It can be used in separation, purification and decontamination processes.
Explain how an AA analysis is carried out and the principles behind how it works.
Atomic Absorption analysis is a procedure to determine the chemical elements using the absorption of light by free atoms in the gaseous state.
What is the "Beer-Lambert Law" and what is its significance in AA?
The Beer-Lambert Law states that if monochromatic radiation is allowed to fall on a solution, then the amount of light absorbed or transmitted is an exponential function of the concentration of the absorbing substance and of the length of the path of light through the sample.
What is the purpose of the "standards" that are run as part of an AA analysis?
Standards are analyzed by AA and the absorbance of each is recorded. The standards are then reanalyzed to see how closely they match the correct values. This helps measure the instrument's accuracy.
What is the problem with analyzing a sample whose absorbance exceeds 1 absorbance unit? What will be done in this experiment to compensate for this problem?
If the sample exceeds one absorbance unit, there is little light transmitted for the PMT to detect. To combat this, the solution can be diluted.
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