What volume of EDTA is used in titrating the Ca2 in the hard water?

Chemistry
Tutor: None Selected Time limit: 1 Day

A 100mL sample of hard water is titrated with EDTA solution in Problem 2 (0.011M). The volume of EDTA required is 31.84 mL. (36.27 mL was needed to titrate Ca2+ in 25mL aliquots from the previous question.)

What's the volume of EDTA used in titrating the Ca2+ in the hard water?

Also, if the Ca2+ comes from CaCO3, how many moles of CaCO3 are there in 1 L of the water? How many grams of CaCO3 per liter?

What is the hardness of water in ppm CaCO3 of 1ppm CaCO3=1mg per L?

Aug 27th, 2015

Thank you for the opportunity to help you with your question!

Volume of EDTA required is 31.84 mL to titrate 100ml sample.

we need to get the moles of EDTA in 31.84ml

in 1000ml =0.011 moles

31.684ml = 31.84/1000 *0.011 moles = 3.534 *10^-4

reacting ratio of EDTA AND Ca2+ = 1:1

moles of caco3 that reacted = 3.534 *10^-4 moles

this moles are in 100ml of water

in 1000ml moles = 1000/100 * 3.534 *10^-4 moles = 3.534 *10^-3 moles

there are 3.534 *10^-3 moles of CaCO3 per litre of water

mass in grams = moles * molar mass

mass in grams = 3.534 *10^-3 * 100g/ mole

=0.3534 gram of CaCO3 per litre of water


ppm = mg/litre

0.3534*1000mg = 353.4 mg/liter = 353.4 ppm

Please let me know if you need any clarification. I'm always happy to answer your questions.
Aug 27th, 2015

Thank you! So just to clarify, the volume of EDTA that is USED in titration is the same as the volume REQUIRED (31.84)?

Aug 27th, 2015

yes it is. If you have further questions please ask me directly. I will be glad to assist

Aug 27th, 2015

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