7. Using Quantitative Analysis Flashcards
What is the use of buffers?
To maintain optimal pH in a system
What is a buffer made up of?
A weak acid and conjugate base or a weak base and conjugate acid
What happens when a strong acid is added to a buffer?
The equilibrium in HA(aq) + H2O(l) ⇌ A−(aq) + H3O+(aq) has an increased concentration of H3O+ ions, meaning the equilibrium will be shifted to the left due to Le Chatelier’s principle, reducing this concentration.
What happens when a strong base is added to a buffer.?
The addition of OH- ions will react with the H3O+ ions in the solution. This will disturb the equilibrium in HA(aq) + H2O(l) ⇌ A−(aq) + H3O+(aq), as there is a decrease in H3O+ and increase in H2O, meaning the equilibrium will shift to the right.
What is the buffer capacity?
The amount of acid or base that can be added before significant change occurs in the pH ([A-]/[HA] is outside of the range 1/10 to 10).
What affects buffer capacity?
The number of moles of weak acid to strong base should be equal, and the actual amount of buffer in the solution.
What are some steps used in titrations of acid to increase validity and reliability?
- Conditioning of burette
- Use of specific indicator
- Repetition
- White paper placed under flask
- Rinse with deionised water
What acid-base titrations use methyl orange, and what is its pH range?
Strong acid - Weak base, 3.1–4.4
What acid-base titrations use phenolphthalein, and what is its pH range?
Weak acid - Strong base, 8.3–10.0
What acid-base titrations use bromothymol blue, and what is its pH range?
Strong acid - Strong base, 6.2–7.6
What does conditioning the burette involve?
Coating the inside of a burette with titrant to ensure the concentration is not compromised
What is the titrant?
The solution in the burette being added
What is the analyte/titrand?
The unknown solution
