Week 4 Primary standards, Secondary standards solutions, Standardization, Stoichiometric relationship, pH calculations

Primary Standards Primary standards are those chemical reagents having high percent purity, stability toward air, having high molecular mass, readily solubility in the solvent, having medium cost and readily availability. A few primary standards are as follow, Potassium hydrogen phthalate (KHP) is used as a primary standard for standardization of NaOH Na2CO3 is used as a primary standard for standardization of HCl Na2C2O4 is used as a primary standard for standardization of KMnO4 Zn pellets or Mg ribbons are used as a primary standard for standardization of EDTA

What is acid-base titration? A TITRATION WHICH DEALS WITH A REACTION INVOLVING ACID AND A BASE. What is a titration? The act of adding standard solution in small quantities to the test solution till the reaction is complete is termed titration.

What is a standard solution? A standard solution is one whose concentration is precisely known. What is a test solution? A test solution is one whose concentration is to be estimated

How hard is it to make 500 mL of 0.1 M NaOH? Should not be that hard right?!! Calculate the weight of NaOH (2.0 g) Weigh out the NaOH on the balance Dissolve it in 500 mL of water in a volumetric flask Hold on! We have a problem here!!

Equivalence point – the point at which the reaction is complete Titrations (Review) In a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete. Equivalence point – the point at which the reaction is complete Indicator – substance that changes color at (or near) the equivalence point Slowly add base to unknown acid UNTIL The indicator changes color (pink)

Calculation of pH Acids are those chemical reagents on dissolution in water produce hydrogen ion (H+). Acids may be strong acids like HCL, H2SO4, and HNO3 or may be weak acids like acetic acid etc. The strong acid is that which completely dissociate into hydrogen ion while the weak acid is that which partially dissociate into hydrogen ion. For acidic solution its strength of acidity can be calculated in term of pH. Experimentally pH can be measured by using an instrument called pH-meter.

For strong acidic solution the pH can be calculated as: Example: Calculate the pH for 0.1M HCl solution Example: Calculate the pH of 0.1N H2SO4 solution.

Example: Calculate the pH for 0. 001N CH3COOH solution of 250ml volume Example: Calculate the pH for 0.001N CH3COOH solution of 250ml volume. Ka value for acetic acid is 1.75 x 105- at 25 Co

Example: Calculate the pOH and pH for 0.01N NaOH of 250ml volume.