Question

A student titrates 25.00 ml. of tap water using 4.86 mL of 0.020 M EDTA. Calculate the hardness of the water

Answer 1

Answer:

0.0038 M

Explanation:

Hardness of the water is generally due to the presence of $CaCO_3$ in water.

At equivalence point

Moles of $Ca^{2+}$ = Moles of EDTA

Considering

$Molarity_{Ca^{2+}}\times Volume_{Ca^{2+}}=Molarity_{EDTA}\times Volume_{EDTA}$

Given  that:

$Molarity_{EDTA}=0.020\ M$

$Volume_{EDTA}=4.86\ mL$

$Volume_{Water\ or\ Ca^{2+}}=25.00\ mL$

So,

$Molarity_{Ca^{2+}}\times 25=0.020\times 4.86$

$Molarity_{Ca^{2+}}=0.0038\ M$