Determining the hardness of water using the titrator

Name 6

Determiningthe hardness of water using the titrator

Thehardness of water is determined by the amount of metallic ions thatare dissolved in it. Hard water is known to contain a high amount ofions while soft water contains minimum amounts of ions. Althoughwater may contain different types of ions (such as SO42-

Ca2+,HCO3, and MG 2+),calcium ions are the most common (Hands-OnLabs, Inc 3). Thehardness of water is expressed in terms of the concentration ofcalcium carbonate dissolved in water. Soft water has a concentrationof between 0-60 mg/L of calcium carbonate while hard water has aconcentration value of between 121 and 180 mg/L of calcium carbonate(SchoolToday 2).This means that the nature of the local tap water can be successfullydetermined in the present experiment by determining the concentrationof calcium carbonate.


Theexperiment was performed in three phases. The first stage involvedthe testing of the indicator, which was accomplished by preparing thebuffer solution. A few grains of EBTR powder were then dipped intothe prepared solution and observations made. The second stage of theexperiment involved the process of titration. The titrator was heldin position and few drops of EDTA solution added into the 500 mlbeaker. The third stage of the experiment involved water titrationwhere buffer solution and tap water were poured into the beaker. TheEDTA solution was then added drop wise into the beaker using thetitrator. Each drop of EDTA was released after 5 seconds until thechange of color to light blue was observed. The process was repeatedin two trials.


Table1: Observations


Initial EDTA Volume (mL)

Final EDTA Volume (mL)

Volume of EDTA used (mL)

Trial 1




Trial 2




Trial 3




Average volume of EDTA used (mL)



Hardnessof the water = (0.4767 mg/mL) x 100 = 47.67 mg/L of CaCO3

Thevalue of the average volume of the EDTA was multiplied by 100 becausethe EDTA’s concentration had been adjusted to so that the amount ofthe EDTA used for each trial of titration represented a given amountof mg / 10 mL of water hardness.


Thepurpose of the experiment was the determination of the hardness oftap water that is supplied locally by assessing the concentration ofsome unknown amount of calcium carbonate in the tap water. Titrationwas used because it is among the most accurate methods of determiningthe concentration of calcium carbonate and other analytes. The valueof 47.67 mg/L of CaCO3 indicates that the tap water was soft becauseits concentration of calcium carbonate was within the range of 0-60mg/L.

Therewere several possible sources of error in the present experiment. Forexample, vigorous swirling could lead to splashing out of thesolution, which could reduce the accuracy of the results. The secondpossible source of error is the possibility of the presence ofresidual compounds in the beaker, which could compromise the accuracyof results. Another possible source of error is the presence of airbubbles in a titrator, which could interfere with the accuracy of theresults.


Thepurpose of the present experiment was to determine the hardness ofthe tap water using the process of titration. The experiment wasperformed in three trials with the objective of reducing the effectof errors. The concentration of EDTA was adjusted in order tosimplify calculations and values recorded during the calculation. Thehardness of the local tap water (47.67 mg/L of CaCO3) was obtainedmultiplying the average value of the volume of EDTA obtained by 100.Trials are important in an experiment because they minimize theeffect of error. This is because the average value of the threetrials is likely to have a minimum error compared to each of theindividual trials.

Answersto additional questions:

1.Based on your analysis of the local water, how could you classify itshardness?

Thelocal tap water could be classified as soft water. This is becauseits hardness value is within the range of 0-60 mg / L (Tiwari 1).From the calculations, the hardness of the local tap water was 47.67mg / L, which indicates that it is soft water.

2.How much amount of calcium could you consume by drinking eight ounceglasses of the local tap water? (One ounce of fluid = 29.57 mL, whichis approximately 30 mL).

8fluid ounce = 8 x 29.57 mL = 236.56 mL

236.56mL x 47.67 mg/mL = 11276.82 mg of calcium

Thisimplies that a person taking eight ounces of the local tap water willconsume about 11,276.82 mg of calcium.

3).Look up the minimum daily requirements of calcium and compute thepercentage of the daily requirements that will be met by consuming1.0 liters of the local tap water.

Therecommended amount of calcium is between 1,000 and 1,500 mg.


1liter = 1,000 mL

47.67mg / ML * 1,000 mL

=47,670 mg of calcium

(47,670mg / 1,500 mg) * 100

=3,178 % of the daily requirements of calcium

d).suppose the air bubble was initially trapped in the tip of atitrator. During the process of titration, air bubble was passed froma titrator. Will the hardness of tap water be reported too low, toohigh, or remain unchanged? Explain.

Thehardness of the tap water will be reported as being too low. The airbubble in the burette would influence the amount of EDTA, which willmake the amount of EDTA lower. This means that the amount reportedvalue of water hardness will also be low.

4).the endpoint was overshot. This made the solution to turn blueinstantly. How will the error affect the value of hardness reported,too low or too high? Explain.

Thevalue of water hardness that is reported will be too high if theendpoint was overshot. The change of color to blue instantly meansthat the amount of EDTA was more than the amount that would beneeded. Therefore, the value of water hardness that is reported willbe too high.


Hands-OnLabs, Inc. Determinationof water hardness using a titrator.Englewood, CO: Hands-On Labs, Inc, 2012.

SchoolToday. Hard water or soft water? SchoolToday.2014. Web. 19 July 2015.

Tiwari,N. Hard water versus soft water. Chemistry.2014. Web. 19 July 2015.