What is pH?

 pH can be defined as 

  •  Concentration or Potential of hydrogen iron 
  •  It's measures value which indicates the degree of acidity of an aqueous solution.

pH term is used to define the scale of acidity or alkaline in liquid.

 acid liquid has lower pH value and basic liquid have higher pH value at room temperature. 

 pH value can be measure between 0 to 14

There are two types of pH 

 ACID: Acid substance always donates hydrogen ions. because when an acid is dissolved in water. the balance between hydrogen ions of acid and hydroxide ions of water is shifted. now there are more hydrogen irons than hydroxide ion in the solution, this kind of solution will make. 

 Characteristics of Acid
  
1. Sour taste
2. Unpleasant 
3. inedible/undrinkable
4. bases turn blue litmus paper red 

 The degree of acidity is due to the presence of H+ ions

 Example:  tomato juice,  black coffee, urine, milk, acetic acid(vinegar)


BASE: A Base substance always accepts hydrogen ions. because when a base is dissolved in water,  the balance between hydrogen ions of acid and hydroxide ions of water is shifted to the site way. now there are more hydroxide irons than hydrogen ion in the solution, this kind of solution will make.

Characteristics of BASE 

 1. Bitter taste
2. Feels like "soap water"
3. Bases turn red litmus paper blue.

 The degree of alkalinity is due to the presence of OH- ions

 examples: sodium bicarbonate(baking soda) 


 pH calculation 

 Basic Eqution of pH :

  log  __1___  = log(1) - log(H30+) = - log (H30+)
        [H30+]

 Thus the pH defines as the negative logarithm of hydrogen ion concentration.
pH scale
  • A scale developed to measure the concentration of hydrogen ion in a solution is known as pH scale where p in pH implies ‘potenz’ in German.
  • pH scale ranges from 0 (highly acidic) – 14 (highly alkaline).
  • The pH of a neutral solution is 7.
  • Acidic solution is represented by a value of less than 7 on the pH scale.
  • Whereas basic solution is represented by a value greater than 7 on the pH scale.
  •  An increase in OH– ions concentration in the solution results in increase in the strength of alkali hence the value of pH increases.
  • Acids giving rise to more H+ ions are strong acids whereas those giving rise to less H+ ions are termed as weak acids.
  • Similarly bases giving rise to more OH- ions are strong bases whereas those giving rise to less OH- ions are termed as weak bases.
  • Salts of a strong acid and a strong base are neutral with pH value of 7.
  • Salts of strong acid and weak base are acidic with a pH value of less than 7.
  • Salts of a strong base and weak acid are basic in nature, with a pH value of more than 7.


  pH Use
  • Environment and water utilities 
  • Tap water 
  • Industrial water  
  • Wastewater 
  • Chemical process
  • Swimming pools
  • Nuclear power plant 
  • Food and beverage industries
  • Pharmaceutical and cosmetic industry


 Buffer solution 

  • Buffer solutions are used to calibrate ph meter because they resist change in ph.
  • when you use ph meter to measure ph, you want to be sure that if the meter says ph=7 the ph is really is 7.00
  • Buffers are mixtures of compounds that resist changes in ph by their presence upon 
  •  the addition of small quantities of acid or alkali 

 Types of buffer 

Acidic buffer: it is a combination of the weak acid and its salt with a strong base
  • ex: CH3COOH/CH3COONA, H2CO3/NaHCO3, H3PO4/NaH2PO4, HCOOH/HCOONa
Basic buffer: it is a combination of a weak base and its salt with the strong acid

  • ex: NH4OH/NH4CL , NH3/NH4CL , NH3/(NH4)2CO3

 INECESSITY OF A BUFFER SYSTEM 


  • It is necessary to prepare a definite PH solution and stored 
  • Sometimes the preservation of this solution is more difficult than its preparation 
  • If the solution comes in the contact with air, it will absorb co2 and becomes acidic.
  • If the solution is stored in a glass bottle, alkaline impurities from the glass may be an effect on pH.  
  • In general case buffer solution packed in plastic bottle or pouch as per ml(milliliters)
  • It is necessary to maintain the temperature of the buffer solution while measuring or calibration that temperature instruction chart mention on the bottle or in the sheet.
  • Don't use previous buffer solution for next measurement after so long  


Electrode


  • ph electrode measurements made by comparing the reading with sample and Ph buffer define solution
  • When a pH sensing electrode comes in contact with the sample, a potential develops across the sensing membrane surface and that membrane potential varies with Ph.second electrode is unvarying.it fix with its PH buffer

  • Calibration of the seconde electrode has fixed their pH value with reference to this electrode, ph of the sample will measure the difference between two electrodes generate MV and that MV converted to Ph units shows on the display