Acid/Base Titrations Flashcards
What is meant by a solution?
A uniform mixture of two substances.
e.g. Sea water
Distinguish between ‘concentrated’ and ‘dilute’ solutions.
- Concentrated solutions contain a relatively large amount of solute per litre of solution.
- Dilute solutions contain relatively less solute per litre solution.
Define ‘concentration’.
The amount of solute per set amount solution.
Denoted by ‘M’ - moles per litre solution or ‘molarity’
To what does ‘p.p.m.’ refer?
What is it used for?
Parts of solute per million parts solution. It is often used for extremely dilute solutions (composition of water).
(1 ppm = 1 mg per litre)
What is a standard solution?
A solution whose concentration is accurately known.
What are primary standards and what are they used for?
- They are water-soluble substances that are pure and stable.
- They are used to make up standard solutions.
(Anhydrous sodium carbonate is usually used due to its purity, stability, and solubility in water)
For what purpose is a volumetric flask used?
When it is filled to the calibration mark, the volume of the substance is then accurately known.
Describe the procedure of setting up a burette.
- Wash the burette w/ deionized water then with the solution (prevents dilution/contamination).
- Allow some solution to flow through the tap into a waste beaker (removes air bubbles).
- Clamp vertically and read meniscus at eye level for accuracy.
Why is a wash bottle normally used in titration experiments?
It is used for accuracy - so that no solution is lost when being dissolved or transferred to a new container.
Describe the preparation of a pipette for the titration.
- Rinse with deionized water then with solution.
- Always use a pipette filler (toxic substances).
- Touch the side of the conical flask and release the solution.
- Ignore last drop as it is already accounted for in the graduation.
Describe the preparation of a titration (conical) flask for the titration.
- Wash with deionized water ONLY (no extra moles added).
- Place over white tile to observe colour change clearly.
- Wash down the sides of the flask with deionized water while swirling (during titration) to ensure accurate colour change.
What occurs during a ‘titration’?
Two known volumes of two substances are added to each other.
One is a standard solution (concentration is known).
One is added to a burette (acid) and dropped steadily into a beaker of the other (base).
An indicator is added that changes colour at the end point.
The volume of the burette substance needed to change the colour is used to calculate the concentration of one of the substances.
This is done using the formula:
V1 x M1 x n2 = V2 x M2 x n1
What are the applications of acid-base titrations?
- Can be used to find concentration of everyday acids/bases.
- Can be used to quantify water of crystallisation in hydrated sodium carbonate.
- Can be used in preparation of a salt.
- Can be used to determine Mr of an acid/base.
Why is it that dilute (or at least not highly concentrated) substances are used for titrations?
If a highly concentrated substance is used, the colour change may occur far too quickly in the titration, increasing error margin.
What volume of ethanol exists in a 500ml can of beer with 4% (v/v)?
4% (v/v) means 4cm^3 ethanol in 100cm^3 beer.
Beer has a density of roughly 1g/cm^3, so 500ml = 500cm^3.
4cm^3 x 5 = 20cm^3 ethanol in 500ml beer.
