School of Engineering Department of Civil Engineering

___________________________________________

CIE 425 Environmental Engineering Lab

pH-Alkalinity & Acidity

Lab Report#: 1 Section: M11

By: Omar Fares Roy Fares Paolo el Khoury

Due Date: Monday 13 October 2014 Grade:

/20 ABSTRACT:

In this experiment we measure the alkalinity and acidity of a given solutions by using titration agents.The different end points are determined by changes in pH which can be recognized using different indicators. The data we obtained lead to certain results that are to be illogical .Our samples had very low alkalinity and acidity meaning that the addition of small amounts of base or acid will lead to a major pH variation.

Introduction:Acidity and alkalinity measurements are used to assist in establishing levels of chemical treatment to control scale, corrosion, and other adverse chemical equilibrium.

Levels of acidity or alkalinity are critical in establishing solubility of some metals, their toxicity, and the buffering capacity of some water sources such as lakes, pounds, natural tanks, water behind dams….

The case of the use of water in daily shores in societies, water shouldn’t be acidic or basic , it should fall in certain range of PH around 7 to be safe for

usage.

Three test methods cover the determination of acidity or alkalinity of all types of water:

1

Background and Theory:(i) Alkalinity: The alkalinity of the water is a measure of its capacity to neutralize acids. The alkalinity of natural waters is due primarily to the salts of week acids. Bicarbonates represent the major form of alkalinity. alkalinity of many surface waters constitute of carbonates, bicarbonate and hydroxide contents, it is assumed to be an indicator of these constituents as well. Alkalinity in excess of alkaline earth metal concentrations is significant in determining the suitability of water for irrigation. Alkalinity measurements are used in the interpretation and control of water and wastewater treatment processes. Raw domestic wastewater has an alkalinity less than or only slightly greater than that of the water supply. (ii) Acidity: Acids contribute to corrosiveness and influence chemical reaction rates, chemical speciation and biological processes. Acidity of water is its quantitative capacity to react with a strong base to a designated pH. The measured value may vary significantly with the end point pH used in the determination. When the chemical composition of the sample is known study mineral acids, weak acids such as carbonic and acetic and hydrolyzing salts such as iron or aluminum sulfate may contribute to the measured acidity according to the method of determination. Mineral acidity: It is measured by titration to a pH of about 3.5, the methyl orange end point (also known as methyl orange acidity). Total acidity: Titration of a sample to the phenolphthalein end point of pH 8.3 measures mineral acidity plus acidity due to weak acids, thus this is called as total acidity (or phenolphthalein acidity). In water analysis, this test does not bear significant importance because methyl orange acidity invariably remains absent in the raw water and even phenolphthalein acidity (that too principally due to the excessive-prevalence of dissolved carbon dioxide and carbonic acids) normally does not exist to a significant extent in the raw water.

List of Equipment and chemicals:- Beakers- pH meter- Magnetic stirrer (with a stirring bar)

2

- Buffer solution- Distilled water- Burette (or pipette) - Indicators: phenolphthalein and methyl orange- H2SO4 solution (0.1 N)- NaOH solution (0.1 N)

Procedure

PH Experiment:

Before the pH of a solution can be measured, the pH meter must first be calibrated (once every few hours). Place the buffer solution of pH = 7.0 (that comes with the pH meter) in a small beaker, then place the electrode of the pH meter into the beaker and measure the pH of the solution. If the pH meter shows a pH of 7.0, this means that it is calibrated. If the pH meter shows a pH different from 7.0, use the analog knob (dial) to change the intercept manually on the pH meter in order to change the displayed pH until it displays a pH of 7.0.

Then, place some distilled water in another beaker and place the electrode in that beaker in order to clean it before using it on another solution. Measure the pH of the different solutions by placing the electrode in the beaker and stirring by hand.

Alkalinity Experiment:

Alkalinity is the capacity to neutralize acids which is caused by ions in solution which can accept hydrogen ions and thus neutralize them tending to maintain the same pH, i.e. buffer solution. Total alkalinity (TA) measures alkalinity from OH-, HCO3-, and CO32-, whereas phenolphthalein alkalinity (PA) measures alkalinity measures alkalinity contributed by only OH- and CO32- ions.

Place a 50 ml of a basic solution (NaOH) into a beaker and add a few drops of phenolphthalein into it. Place a stirring bar in the beaker, place the beaker on a magnetic stirrer and turn the stirrer on. Place a burette (or pipette) containing an

3

acidic solution (titrant) of H2SO4 (0.5 N) over the beaker. The solution in the beaker is now pink in color. Place the electrode of the pH meter in the beaker (pH was 11.33) and start adding the titrant onto the solution in the beaker one drop at a time and observe the pH value displayed as well as the color of the solution. Continue adding drops of titrant into the beaker until the pH displayed becomes 8.3 (i.e. until the solution becomes colorless). Record the volume of titrant (2.6 ml) used until now under PA, ml. Then, add a few drops of methyl orange onto the same sample in the beaker (the color becomes yellow) and continue adding the titrant until the pH becomes 4.5 (i.e. until the color becomes pinkish-orange). Stop the titration and record the volume of titrant (2.9 ml) used until now under TA, ml.

Acidity Experiment:

Acidity is the capacity to neutralize bases which is usually used to describe a water that has a high content of mineral acids.

Place a 50 ml of an acidic solution (H2SO4) into a beaker and add a few drops of methyl orange into it. Place a stirring bar in the beaker, place the beaker on a magnetic stirrer and turn the stirrer on. Place a burette (or pipette) containing a basic solution (titrant) of NaOH (0.1 N) over the beaker. The solution in the beaker is now pinkish-orange in color. Place the electrode of the pH meter in the beaker (pH was 1.79) and start adding the titrant onto the solution in the beaker one drop at a time and observe the pH value displayed as well as the color of the solution. Continue adding drops of titrant into the beaker until the pH displayed becomes 4.5 (i.e. until the solution becomes yellow in color). Record the volume of titrant (10.4 ml) used until now under MA, ml. Then, add a few drops of phenolphthalein onto the same sample in the beaker (the color remains yellow) and continue adding the titrant until the pH becomes 8.3 (i.e. until the color becomes pink). Stop the titration and record the volume of titrant (10.8 ml) used until now under CDA, ml.

4

ResultspHSample pH Acid/Neutral/Base

NaOH 8.86 Base

NaCl 8.69 Base

Tape water 7.95 Base

Ethanol 6.00 Acid

5

H2SO4 2.36 Acid

CaCO3 7.27 Neutral

LitmusRed Litmus Blue Litmus Yellow Litmus

NaOH Blue No change Blue

H2SO4 No change Red Red

Calculations:Alkalinity

Vs: Volume of sample in mL=50mL Vt: Volume of H2So4 added in mL ,

For PA=31 mL For TA=37 mL

N: the normality of the titrant (H2SO4)=1

Phenolphthalein alkalinity, mg/L as CaCO3 = (PA) = (N) ×(Vs ×10-3)/Vt = (0.1 × 50 ×10 -3)/31 = 1.61×10 -4 mg/L

Total alkalinity, mg/L as CaCO3= (TA)= (N) × (Vs×10-3)/Vt

6

= (0.1 × 50 × 10-3)/39 = 1.35×10-4 mg/L

Approximately P=T, then from table 1 in the handout we can determine the type of alkalinity:Titrationresults

Types of Alkalinity as CaCO3

OH- HCO3- CO3

2-

P=T T=1.35×10-4

mg/L0 0

Acidity:Vs: Volume of sample in mL = 50 mLVt: Volume of NaOH added in mL, For MA= 55 mL For CDA= 57.5 MlN : the normality of the titrant (NaOH)=0.3Mineral Acidity, mg/L as CaCO3= (MA) = (N) × (Vs×10-3)/Vt

= (0.3 × 50 ×10-3)/55 = 2.73×10-4 mg/L

CO2 Acidity, mg/L as CaCO3= (CDA) = (N) * (Vs*10-3)/Vt

= (0.3 * 50 * 10-3)/57.5 = 2.61*10-4 mg/L

DISCUSSIONIn the experiment performed we computed the alkalinity and acidity of a water sample.These 2 parameters are very important in determining water quality.Acidity isa measure of an aggregate property of water and

7

can be interpreted in terms f specific substances only when the chemical composition of the sample is known.Acidity may contribute to corrosiveness and influence chemical reaction rates ,chemical speciation and biological process. In addition to effects on human beings,  water with high alkalinity can cause other problems. Bicarbonates and carbonates can clog the nozzles of pesticide sprayers and drip tube irrigation systems with obvious effects.  In general, water for irrigation should have a pH between 5.0 and 7.0. Water with pH below 7.0 is termed "acidic" and water with pH above 7.0 is termed "basic"; pH 7.0 is "neutral"

The values obtained in our experiment are very low compared to these values.With a very large error.This huge error might be due to an error in the given formula or to an error in its application .Concerning the experimental procedure many errors related to accuracy and precision may have occurred.Such errors can be due to the presence of some residues of other solutions in the beakers and titration devices.In addition volume readings and end point determination may not be precise.

APPENDIX1.described above2.Water can have a wide pH range. Phenolphthalein which is colorless below 8.3 will not colorate in water with pH less than 8.33.Because we are measuring two alkalinity values for the same sample.Each alkalinity value corresponds to a different pH.Since methyl

8

orange changes color at a pH of 4.5 which coincides with the TA end point , we select this solution as our indicator.4.No to measure the pH of a solution it is not necessary to know its volume because 1ml of solution has the same pH as 1L of the same solution.5.PA has an end point with a pH=8.3 starting from a sample with higher pH.TA requires from us to reach pH of 8.3 starting with a sample of pH greater than 4.6.Hence it is impossible to measure TA from a sample used in PA6.Yes chloride is a negatively charged ion that is able to accept a proton hence it will contribute to alkalinity.7. Alkalinity is a measure of the amount of acid required to drop the pH to approximately 8.3 . Higher alkalinity resists acidic changes in pH high pH indicates high alkalinity

References

http://www.veoliawaterstna.com/crownsolutions/ressources/documents/2/21951,Water-pp393-394.pdfhttp://www.advancedaquarist.com/2002/5/chemistryhttp://web.iitd.ac.in/

9