What cations are responsible for water hardness?
The cations responsible for water hardness are Ca2+ and Mg2+.
Experimental Procedure, Part A.1. Calculate the mass of disodium ethylenediaminetetraacetate (molar mass = 372.24 g/mol) required to prepare 250 mL of 0.010 M solution. Show the calculation. Express the mass to the correct number of significant figures.
![card image](../uploads/119/20/69c107f6_144910d43f1__8000_00000232.png)
Experimental Procedure, Part A.3. A 25.7-mL volume of prepared Na2H2Y solution titrates 25.0 mL of standard 0.0107 M Ca2+ solution to Eriochrome Black T endpoint. What is the molar concentration of the Na2H2Y solution?
![card image](../uploads/120/21/69c107f6_144910d43f1__8000_00000239.png)
Which hardening ion Ca2+ or Mg2+ , binds more tightly to (forms a stronger complex ion with) the Eriochrome Black T indicator used for today's analysis?
Periodic trends show that as you move down the rows the lattice energy decrease. Therefore, Mg should have a higher lattice energy then Ca and because of this Mg will form a stronger complex ion with the Black T indicator.
What is the color change at the endpoint?
Sky Blue.
Calculate the moles of hardening ions in the water sample.
![card image](../uploads/121/22/69c107f6_144910d43f1__8000_00000240.png)
Assuming the hardness is due exclusively to CaCO3, express the hardness in mg CaCO3/L sample.
![card image](../uploads/122/23/69c107f6_144910d43f1__8000_00000241.png)
What is the hardness concentration expressed in ppm CaCO3
1 mg CaCO3/L = 1 ppm
356.3 ppm of CaCO3
Classify the hardness of this water according to Table 9.1.
Very hard water
Determine the number of moles of hardening ions present in a 100-mL volume sample that has a hardness of 58 ppm CaCO3.
![card image](../uploads/123/24/69c107f6_144910d43f1__8000_00000242.png)
Determine the number of moles of hardening ions present in a 100-mL volume sample that has a hardness of 58 ppm CaCO3.
![card image](../uploads/124/25/69c107f6_144910d43f1__8000_00000243.png)
What volume of the 0.100 M Na2H2Y is need to reach the Eriochorme Black T endpoint for the analysis of the solution.
![card image](../uploads/125/26/69c107f6_144910d43f1__8000_00000244.png)
Water hardness is also commonly expressed in units of grains/gallons, where 1 grain/gallon equals 17.1 ppm CaCO3. Express the hardness of this "slightly hard" water sample in grains/gallon.
58 ppm/ 17.1 ppm = 3.39 gpg