Question

Experiment : Determination of Water Hardness Using a Titrator

EDTA 0.010 M used for the experiment

the titrator with 7–9 mL of distilled water. = I used 9mL

the graduated cylinder to measure exactly 10 mL of tap water from your faucet.

Add 5 drops of pH 10 buffer solution to the 10 mL of tap water in the beaker

Dip approximately 10 mm of a toothpick into the distilled water. Then, while toothpick is still damp, dip the toothpick into the EBT indicator powder.

Dip the EBT-covered toothpick end into the water in the beaker and carefully stir, to transfer all of the EBT from the toothpick into the water.

Carefully swirl the beaker for 30–60 seconds to fully dissolve the EBT into the water solution. The EBT indicator will cause the water solution to turn a pale purple-pink color.

Open the stopcock and add 1 drop of (EDTA 0.010 M) to the purple-pink water sample in the beaker. After the drop is added, gently swirl the beaker and observe the color for 5 seconds.

And repeat this trial 3 times of titration  

• Using the following equation, determine the average concentration (moles per liter) of Ca2+ ions present in your water. Record the concentration in Data Table 2.

mol Ca2+L =L EDTA × mol EDTAL × 1 mol Ca2+1 mol EDTA × 10.010 L water

Note: PPM is equivalent to mg/L for dilute solutions.

ppm CaCO3 = mol Ca2+1L×1 mol CaCO31 mol Ca2+×100.06 g CaCO31 mol CaCO3×1000 mg1g

Please help what should I be getting for these questions based on my results. explain also is 28 ppm Correct? For the first table

Average volume of EDTA USED (mL)	Concentration Ca+ ions per liter of water (mol/L)	Water Hardness (ppm CaCO3)
2.6 mL	0.02888 mol/L	28 ppm ? (not sure if this is correct)

  

Initial EDTA Volume mL	Final EDTA Volume mL	Total Volume used
9 ml	8 ml	1 ml
8 ml	7.7	0.3
7.7	6.4	1.3
	Average volume of EDTA Used mL =	2.6

QUESTIONS

1. Based on the analysis of your local water, would you classify its hardness as soft, moderate, hard, or very hard? Explain your answer.

2. Approximately how much calcium would you ingest by drinking eight 8-oz glasses of your local water? Hint: 1 oz (fluid ounce) = 29.57 mL.

3. Assume an average minimum daily requirement for calcium is 1,150 mg. Calculate what percentage of your daily requirements could be met by drinking 1.0 L of your local water.

Answer 1

The calculated values for concntratiion of Ca²⁺ and hardness are not correct.

Concentration of Ca²⁺ can be calculated from v₁s₁=v₂s₂ formula

where v₁ = volume of EDTA = 2.6 mL

v₂= volume of Ca2+ solution = 10.01 mL

s₁= Concentration of EDTA = 0.01 M (provided)

s₂= Concentration of Ca²⁺

Now Concentration of Ca²⁺ =s₂= v₁s₁/v₂ = 0.01x2.6/10.01 = 0.0026M

1000 mL of 1M EDTA = 100 g of CaCO₃ (molar mass of CaCO₃ = 100 g)

2.6 mL of 0.01M EDTA= 100x2.6x0.01/1000 = 0.0026 gm

Amount of CaCO₃ in 10 mL hard water solution= 0.0026 gm

Now, 1 ppm= 1 mg in 1 litre or 1 mg in 1000 mL

Therefore, Amount of CaCO₃ in 1000 mL hard water solution= 0.0026x1000/10 gm in  

= 0.0026x1000x1000/10 mg/mL

= 260 ppm

Hence from this value, we can say that the local water is hard. Since according to geological survey any water that has less than 60 ppm of CaCO3 mass equivalents is generally considered soft water.

8-oz = 8 x 29.57 mL =236.56 mL

Total CaCO₃ present in 236.56 mL water = 0.0026x236.56/10 = 0.0615 gm = 61.5 mg

In CaCO₃, 100 gm contain 40.078 gm of Ca

Hence, 0.0615 gm CaCO₃ contain = 40.078x0.0615/100 =0.024 gm of Ca

Therefore, Approximately 0.024 gm calcium can be ingest by drinking eight 8-oz glasses of local water.

1 L of local water contain 0.260 gm of CaCO3.

Hence, 0.26 gm CaCO₃ contain = 40.078x0.26/100 =0.104 gm of Ca

= 104 mg of Ca

Therefore percentage of daily requirement could be met by drinking 1 L water is = 104x100/1150 = 9.04%