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Explain the need for primary and secondary standards in analysis

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Introduction

´╗┐Ardit Cenalia Unit 19 | M1 Explain the need for primary and secondary standards in analysis What is primary standard? A primary standard is a solution of which a concentrated is made from a primary standard. I.E. the substance available in a sufficiently pure from which requires no determination of concentration. A primary standard is one that can be determined to a high level of precision, and reliability. For instance, a typical acid-base titration can be done to determine the concentration of an unknown HCl solution. ...read more.

Middle

Potassium permanganate is an example of a secondary standard. It has to be standardised first, but then it can be used for quantitative analysis, A primary standard substance will not always be used in standardisation; this is because primary standard is a reagent which is very pure, representative of the number of moles the substance contains and easily weighed. For example sodium chloride is used as a primary standard for silver nitrate reaction. For example potassium hydrogen phthalate is used as a primary standard but because weak acid, wouldn?t be used to standardise a weak alkaline, like ammonia solution. ...read more.

Conclusion

Consequence of not having a standard substance. In a reaction between sulphate acid and sodium hydroxide, it is important to know the concentration of one of the reactants in order to determine the concentration of the unknown , base also on mole ration. NaOH+H2SO4ï Na2SO4+2H2O If the volume of sodium hydroxide is known = 25xm3, titre value of acid = 12.80cm3, concentration of sodium hydroxide = 0.5 mole. Number of mole of NaOH = (0.5X25)/1000 =0.0125 moles. Number of moles of H2SO4 = 0.0125/2 = 0.00625 Concentration of H2SO4 = (0.00625X1000)/12.80 = 0.48828125mol/dm3 It is important to know the standard substance by finding its concentration and the use this to find the know concentration. ...read more.

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