Primary Standard and Secondary Standard

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PRIMARY STANDARD AND SECONDARY STANDARD BY, LIPSA SAMAL ASST. PROF (PA & QA), SPLS, CUTM Primary Standards A primary standard is a reagent having the known concentration and used to determine the concentration of the different analyte. Properties • extremely pure • stable • has no waters of hydration • has a high molecular weight. e.g, Some primary standards for titration of acids: sodium carbonate: mol wt. = 105.99 g/mol tris -(hydroxymethyl) amino methane (TRIS or THAM): mol wt. = 121.14 g/mol Some primary standards for titration of bases: potassium hydrogen phthalate (KHP): mol wt. = 204.23 g/mol potassium hydrogen iodate: mol wt. = 389.92 g/mol Some primary standards for redox titrations: potassium dichromate mol wt. = 294.19 g/mol SECONDARY STANDARD • secondary standard is a standard that is prepared in the laboratory for a specific compound or element analysis analysis. • Properties- standardized against a primary standard. • Unknown concentration. • Not pure e.g- Sodium hydroxide Potassium hydroxide Difference Between Primary and Secondary Standard Solution 1. Definition • Primary Standard Solution: Primary standard solutions are solutions made out of primary standard substances. • Secondary Standard Solution: Secondary standard solutions are solutions made specifically for a certain analysis. 2. Purity • Primary Standard Solution: Primary standard solutions are extremely pure (about 99.9%). • Secondary Standard Solution: Secondary standard solutions are not very pure. 3. Reactivity • Primary Standard Solution: Primarystandards are less or not reactive. • Secondary Standard Solution: Secondary standards are reactive than primary standards. 4. Water Absorption • Primary Standard Solution: Primarystandards are not hygroscopic. • Secondary Standard Solution:Secondary standards are somewhat hygroscopic. 5. Applications • Primary Standard Solution: Primary standard solutions are used to standardize secondary standards and other reagents. • Secondary Standard Solution: Secondary standard solutions are used for specific analytical experiments. THANK YOU.

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Titration of Aspirin Tablets
Bellevue College | CHEM& 161 Titration of Aspirin Tablets In this lab, you will determine the percent purity of two commercially available aspiring tablets using an acid-base titration. In general, an acid and a base react to produce a salt and water by transferring a proton (H+): HA (aq) + NaOH (aq) H2O (l) + NaA (aq) (1) acid base salt The active ingredient in aspirin, and the chemical for which aspirin is the common name, is acetylsalicylic acid. To determine the amount of aspirin (acetylsalicylic acid) in a sample, the precise volume and concentration of the NaOH, and the overall reaction, must be known. The NaOH serves as a secondary standard, because its concentration can change over time. To find the precise concentration of the NaOH, it must be titrated against a primary standard, an acid that dissolves completely in water, has a high molar mass, that remains pure upon standing, and is not hygroscopic (tending to attract water from the air). Because sodium hydroxide is hygroscopic, it draws water from its surroundings. This mean one cannot simply weigh out a sample of sodium hydroxide, dissolve it in water, and determine the number of moles of sodium hydroxide present using the mass recorded, since any sample of sodium hydroxide is likely to be a mixture of sodium hydroxide and water. Thus, the most common way to determine the concentration of any sodium hydroxide solution is by titration. Determining the precise concentration of NaOH using a primary standard is called standardization. You will first standardize your NaOH solution, and then use it to analyze aspirin tablets for their aspirin content and purity.
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