Hardness Titration 2

What is the average hardness that is acceptable for drinking water in America?

• 250 mg/Liter

• 500 mg/Liter

• 350 mg/Liter

• 1000 mg/Liter

True or False:

Hardness can be measured by independant determination of Calcium and Magnesium along with a calculation of CaCO₃. Please respond with all answers that apply.

• True along with equivalent from the metals assay.

• True but without equivalent from the metals assay.

• False

• True, along with the equivalent from the metal assay, but this is not normally how it is done at Cove.

What is the most common method for determining hardness?

• A titration involving an indicator that changes from blue to red in color

• A titration involving an EDTA containing reagent that produces a color change when Calcium and Magnesium ions have complexed with EDTA

• A calculation based on Calcium and Magnesium only.

• A titration involving a substance that can enhance the pH balance.

Why is it necessary to add an inhibitor before performing a titration for hardness?

• This addition will help maintain the freshness of the sample

• This addition is just part of the protocol so it should always be done.

• This addition does not really do much but help the buffer work.

• This is done to stabilize the pH of the sample because both EDTA and the indicator are weak acids and could throw off the results.

How must one measure hardness a sample of water known to have too high of a concentration of metals?

• Use an EDTA- containing agent

• Add buffers to the sample

• Add multiple inhibitors to the sample

• Use a non EDTA method such as hardness by calculation

What is recommended to wear when working with effluent samples and reagents?

• Safety glasses, a mask, an OSU cap, and a lab coat

• Safety glasses, an OSU T-shirt, and a lab coat

• latex gloves, safety glasses, covered shoes, lab coat, and a mask when samples have a very bad odor.

• safety glasses, lab coat, and latex gloves

Necessary equipment for testing hardness include:

Please select all that apply:

• plastic cups, 50 mL graduated cylinder

• 10 mL graduated cylinder, 10 mL, 100 mL, and 50 mL syringes

• Magnetic stirrer, stirring bar, and Titration Burette

• 50 mL beaker, 10 mL beaker, and thermometer

True or False:

Water samples that will be tested for hardness should be stored at 4 to -2 degrees celsius and analyzed within 6 months. Samples should always be at room temperature before testing the hardness.

• True

• False

What is true about how Quality Control should be handled? Please select all answers that apply...

• Standard checks are run every 10 samples, or once per batch and are recorded in the log book

• Standard recovery should be 100 + or - 10% and a duplicate error should < or = 10%

• See Cove Aquatic Lab manual section 3, page 40

• Blank and duplicate analysis are run every 20 samples or once per batch if less than 20 samples are run and please see Cove Aquatic Toxicity Laboratory Manual for more information

What is the endpoint color change with a water EDTA hardness titration?

• pure blue to red

• red to pure blue

• pure blue to red to yellow

• Pure green to red