25mL of tap-water is titrated with .00500 M EDTA. 7.95mL of EDTA is required for complete reaction, Whatis the molarity of that total water hardness in the 25mL sample

mols EDTA = M x L = ?

mols EDTA = mols hardness (Ca + Mg)
M hardness = mols/L = mols from above/0.025L

To find the molarity of the total water hardness in the 25mL sample, we first need to understand the reaction that is taking place.

In this case, EDTA (ethylenediaminetetraacetic acid) is used as a complexometric titrant to titrate against water hardness ions (usually calcium and magnesium ions). EDTA forms a complex with these ions, and the reaction is as follows:

Ca2+ (or Mg2+) + EDTA ⇄ CaEDTA (or MgEDTA)

Given that 7.95mL of EDTA is required for complete reaction, we can use the concept of stoichiometry to determine the moles of EDTA reacted.

The moles of EDTA reacted can be calculated using the equation:

moles of EDTA = volume of EDTA (in L) × molarity of EDTA

To calculate the moles of EDTA reacted, we convert the volume of EDTA in mL to L:

7.95 mL × (1 L / 1000 mL) = 0.00795 L

Using the given molarity of EDTA (0.00500 M), we can calculate the moles of EDTA reacted:

moles of EDTA = 0.00795 L × 0.00500 M = 3.975 × 10^-5 moles

Now, since the stoichiometry of the reaction between EDTA and water hardness ions is 1:1, meaning that one mole of EDTA reacts with one mole of water hardness ions, the moles of EDTA reacted also represent the moles of water hardness ions present.

Since the volume of the water sample is given as 25 mL (or 0.025 L), we can calculate the molarity of the total water hardness:

Molarity of water hardness = moles of water hardness ions / volume of water (in L)

Molarity of water hardness = (3.975 × 10^-5 moles) / 0.025 L ≈ 0.00159 M

Therefore, the molarity of the total water hardness in the 25mL sample is approximately 0.00159 M.