R-ATCHE-17

Primary standards generally also have to be easy to measure

e.g. $HCl$ - Can't measure this because its a gas!

Make up an approximate solution from concentrated $HCl$

• Standardise HCl using primary $Na_{2}CO_{3}$ by titration
• This gives us a standardised solution of $HCl$ which we can then use as a primary standard for another titration.

Aliquot: the things in the conical flask.

Rinsing:

• Conical flask - rinse with $H_{2}O$! NOT the solution, we are looking to equalise, hence when we put in say $20mL$ of our primary standard, we know the exact moles inside and can dilute it. IF we rinsed with the solution, then we no longer accurately know the moles inside the aliquot.

• Burette: final rinse with the thing you intend to put in the burette

• Pipette: final rinse with the thing you intend to put in the pipette

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