Standard Solution Preparation

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Primary standard characteristics include:

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1. **Purity**: Must be $100\%$ pure so the mass weighed represents the moles exactly.
2. **Stability**: Must be stable at room temperature and towards oxygen/moisture/light so its concentration doesn't change over time.
3. **Hygroscopy**: Should **not** absorb moisture from the air (non-hygroscopic), as moisture would add unknown weight.
4. **Equivalent Weight**: A **high molar mass** is preferred because it reduces the relative error during weighing on an analytical balance.
5. **Examples**: Potassium Dichromate ($K_2Cr_2O_7$), Oxalic Acid, Sodium Carbonate. (Note: $NaOH$ and $KMnO_4$ are NOT primary standards).

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