Experiment 5

• Experiment 5 is entitled acidity of water
• Objectives: 1) to measure the mineral and total acidity of water
• Why is water’s pH important? 1) It provides an adequate environment for organisms to survive (aquatic creatures prefer a pH range of 6.5-9.0). 2)It can affect the solubility and toxicity of chemicals and heavy metals in the water.
• Acidity of Water -is its quantitative capacity to react with a strong base to a designated pH.
• Functions of an acidic water: • Acids contribute to corrosiveness and influence chemical reaction rates, chemical speciation and biological processes. • Control or remove corrosion-producing substances
• Causes of Acidity: •the presence of strong mineral acids, weak acids (carbonic and acetic acids) and hydrolyzing salts such as that from ferric and aluminum sulfates. • Dissolved carbon dioxide
• Human Factors Influencing pH ● Acid rain ● Point Source Pollution ● Mining ● Increased concentrations of carbon dioxide
• Natural Factors Influencing pH ● Calcium Carbonate ● Ground water ● Precipitation ● Photosynthesis and Respiration ● Season
• Acidity is expressed in pH values, mgCaCO3/L
• How does one measure acidity of water? Titrimetric Methods
• Two types of acidity: mineral acidity and total acidity
• Mineral Acidity -Mineral acidity refers to the strength of mineral acids.
• Total Acidity - measures mineral acidity plus acidity due to weak acids. - the measure of the total number of hydrogen ions present in a substance in the form of fixed and volatile acids
• The pH level of mineral acidity is 3.5 and it's indicator is methyl orange indicator
• The pH level of total acidity is 8.3 and it's indicator is phenolphthalein indicator
• Total acidity is higher than mineral acidity
• Mineral acidity is due to strong mineral acids, like sulfuric acid (H2SO4), Hydrochloric acid (HCl), and nitric acid (HNO3)
• Total acidity is due to strong mineral acids, weak acids and hydrolyzing salts
• Formula for MA and TA (Volume of NaOH in L)(Molarity of NaOH)(1 mol CaCO3 / 1 mol NaOH)(100.09 g / 1 mol CaCO3)(1 mg / 0.001 g) / volume of sample in liters
• CO2 Acidity = TA - MA
• In methyl orange indicator it turn orange in acid and yellow in base, 3.1 - 4.4
• In phenolphthalein it turn colorless in acid and reddish pink in basic, 8.3 - 10
• Calibration is add all the numbers of drops in every trial then divide it
• Sodium thiosulfate (Na2 S2 O3 ) solution is added to the water sample before the addition of indicator and the titration to remove residual chlorine. Residual free available chlorine in the sample may bleach the indicator.
• Sodium hydroxide (NaOH) is used as titrant
• NaOH + H± = H2O + Na±
• CO2 + H2O = H2CO3
• H2CO3 + Ca2± = 2H± + CaCO3