Analysis of Tap water (Hardness)
50.00 mL of tap water was transferred to a 250 mL erlenmyer flask. 10mL of NH3/NH4^+ ph 10 buffer was added to the flask, as well as 6 drops of eriochrome black T indicator. This soln was then titrated with EDTA soln(0.00641M)
Given equations:
1. Ca^2+ + Mg^2+ --> Ca^2+ + Mg(Indicator)
2. Mg(Indicator) + Ca^2+ + EDTA^4- --> CaEDTA^2- + MgEDTA^2- + free indicator
QUESTION TO BE ANSWERED
For the volume of titrant used (9.95 mL) calculate the:
a) Ca^2+ + Mg^2+ in sample (mol)
b)[Ca^2+] + [Mg^2+] of sample (M)
The equations 1 & 2 were given, and I believe we are supposed to make an equation for the reaction from this i.e. add them so that:
Ca^2+ + Mg^2+ + EDTA --> MgEDTS^2- + CaEDTA-
So by using the given volume of titrant (EDTA=9.95 mL) we could find the mol of Ca and Mg...i'm just not sure how to go about doing this (the stoichiometry is confusing me since the concentration they are looking for is Ca and Mg added...)
moles EDTA = M x L.
moles Ca + moles Mg = moles EDTA
molarity Ca + Mg = moles/0.050 L = ??
thank you so much for your help!!
To calculate the amount of Ca^2+ and Mg^2+ in the sample, we need to use the stoichiometry of the reaction between the metal ions and EDTA. Let's break down the steps to find the answers to parts a) and b):
Step 1: Calculate the moles of EDTA used
Given:
Volume of EDTA solution used = 9.95 mL = 0.00995 L
Concentration of EDTA solution = 0.00641 M
Moles of EDTA used = concentration * volume
Moles of EDTA used = 0.00641 M * 0.00995 L
Step 2: Use stoichiometry to find the moles of Ca and Mg
From the balanced equation: Ca^2+ + Mg^2+ + EDTA -> MgEDTS^2- + CaEDTA-
We can see that for every 1 mole of EDTA, we react with 1 mole of Ca^2+ and 1 mole of Mg^2+.
Thus, the moles of Ca and Mg are equal to the moles of EDTA used.
Step 3: Calculate the moles of Ca^2+ and Mg^2+ in the sample
The moles of Ca^2+ + Mg^2+ in the sample = Moles of Ca + Moles of Mg
(assuming equal concentrations of Ca^2+ and Mg^2+ in the sample)
Step 4: Calculate the molar concentration of Ca^2+ + Mg^2+ in the sample
Now that we have the moles of Ca^2+ + Mg^2+ in the sample, we can calculate the concentration using the volume of water used (50.00 mL = 0.0500 L) to dilute the sample.
Molar concentration of Ca^2+ + Mg^2+ in the sample (M) = (moles of Ca^2+ + Mg^2+) / volume of water used
By following these steps, you should be able to calculate the answers to parts a) and b) using the given information.