Question

There are many different primary standards that could be used in a standardization titration.

1. What are the criteria of a primary standard?

2. What are three other primary standards besides citric acid?

3. Is citric acid a greener standard than these?

    Please explain this to me, I don't understand it.

Answer 1

1. primary standard solution: A solution of accurately known concentration, prepared using standard substances in one of several ways. A primary standard is a substance of known high purity which may be dissolved in a known volume of solvent to give a primary standard solution.

Features of a primary standard include:

1. High purity
2. Stability (low reactivity)
3. Low hygroscopicity (to minimize weight changes due to humidity)
4. High equivalent weight (to minimize weighing errors)^[3]
5. Non-toxicity
6. Ready and cheap availability

2) The three other primary standards besides citric acid are

• Benzoic acid for standardisation of waterless basic solutions: ethanolic sodium and potassium hydroxide, TBAH, and alkali methanolates in methanol, isopropanol, or DMF
• Potassium bromate (KBrO₃) for standardisation of sodium thiosulfate solutions
• Potassium hydrogen phthalate (usually called KHP) for standardisation of aqueous base and perchloric acid in acetic acid solutions

3) Yes, citric acid is a greener standard than the above mentioned compounds.