All I need is help calculating the Hardness of the water as ppm CaCO 3 = from th

Question

All I need is help calculating the Hardness of the water  as ppm CaCO3= from the part IV data table. I just included the rest in case you needed the info

Part I:

i.Prepare working standard solution 600 ppm CaCO3 by pipetting 25 mL of the 2400 ppm solution into the 100 mL volumetric flask, then dilute to mark and mix well.

Part II:

i.Create a collect data from a blank solution. Start by adding 25 mL of distilled water into an Erlenmeyer flask. Pipet exactly 2 mL of the 4 mM Mg2+ solution, add 12 drops of the indicator solution, add NH3/NH4+ buffer until the pH of the solution is 10 using pH paper to check this.

ii.Titrate, record data, then repeat the titration on a second blank sample. Average the results ensuring that the two end point volumes vary within mL or less.

Part II Data

Trial

Titration Volume (mL)

1

1.2

2

1.0

Average:

1.1

Part III:

i.Standardize the EDTA Titrant. Begin by pipetting a 25 mL portion of the 600 ppm CaCO3 standard solution into an Erlenmeyer flask. Pipet 2 mL of the 4 mM Mg2+ solution, 12 drops of the indicator solution, and add NH3/NH4+ buffer until the pH is 10 as indicated by the pH paper.

ii.Titrate, record data, then subtract the average blank titration volume determined in step 2. Repeat process on a second standard solution, and average the results. The two endpoint volumes should vary within mL or less.

Part III Data

Trial

Total Volume (mL)

Total Volume – Volume from Blank (mL)

1

16.2

15.1

2

16.4

15.3

Average:

15.2

Part IV:

i.Titrate the laboratory unknown. Begin by obtaining 15 mL of the unknown from the instructor and place it into a 100 mL volumetric flask. Dilute to the mark and mix well. Pipet 25 mL of the diluted unknown into an Erlenmeyer flask. Pipet 2 mL of the 4 mM Mg2+ solution, 12 drops of the indicator solution, and add NH3/NH4+ buffer until the pH of the solution is 10 as indicated by the pH paper.

ii.Titrate, record data, and repeat on a second and third aliquot of the unknown. Subtract the blank volume determined in step 2 from each result.

iii.Calculate the hardness as ppm CaCO3 for each titration data, by proportion of volume used compared to the 600 ppm standard.

Determine the average, standard deviation, and the 95% confidence interval for this data.

              Part IV Data

Trial

Total Volume (mL)

Total Volume – Volume from Blank (mL)

1

10.7

10.7-1.1 = 9.6

2

9.8

9.8-1.1 = 8.7

3

10.2

10.2-1.1 = 9.1

           

            Calculations:

            Hardness as ppm CaCO3=

Part V:

i.Report the water hardness in the 15 mL unknown, and determine if the unknown is “hard” or “soft” water.

Trial

Titration Volume (mL)

1

1.2

2

1.0

Average:

1.1

Explanation / Answer

Calculation of the hardness as ppm CaCO3 involves following steps:

1. Calculate the molarity of standard calcium solution.

we have 600 ppm CaCO3 solution

so, 600 ppm = 600mg/L = 0.6g/L

divide this by molar mass of CaCO3 (100 g) to get the molarity.

so, 0.6g/L*1molCaCO3/100g*1molCa2+/1molCaCO3 = 0.006M Ca2+ solution

2. Calculate the molarity of EDTA(EDTA standardization):

you have molarity of calcium solution, so get the molarity of EDTA by using M1V1=M2V2

molarity of EDTA = 25mL*0.006M Ca2+/15.2 mL EDTA = 0.009868M EDTA

3. Calculate Ca2+ concentration in diluted unknown solution.

i) 25 mL of diluted unknown solution required 9.6 mL of 0.009868M EDTA

0.009868mol/L EDTA * 0.0096L/1 * 1molCa2+/1mol EDTA = 0.0000947moles ..............(EDTA reacts with Ca2+ in 1:1 ratio)

0.0000947mol Ca2+ *1molCaCO3/1mol Ca2+ * 100gCaCO3/1molCaCO3 = 0.00947g CaCO3

ppm CaCO3 = mg CaCO3/L solution = 0.00947g CaCO3*1000mgCaCO3/1g CaCO3 * 1/0.025L solution = 378.8mg/L

Thus, hardness as ppm CaCO3 = 378.8

ii) 25 mL of diluted unknown required 8.7 mL of 0.009868 M EDTA

follow the same steps as in i) and we get the value of ppm CaCO3 = 343.4 ppm

iii) 25 mL of diluted unknown required 9.1 mL of 0.009868 M EDTA

hardness as ppm CaCO3 = 359.2 ppm

by multiplying with dilution factor we get the hardness in the original sample that is in 15 mL.

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