Titrations

What is a titration?

A chemical process through reacting a substance with known concentration and volume to determine a substance with unknown concentration

What is a primary standard?

A solid acid or base that meets a criteria

What are the properties of primary standards?

• Readily available in high purities

• Precise formula

• Doesn’t react with surrounds (air/water) hygroscopic and deliquescent

• Has a high molar mass

• Soluble in water

Can hydrochloric acid be an appropriate primary standard?

No because it is volatile and difficult to store in a stable state or pure state

Examples of primary standards

Oxalic acid dihydrate (H₂C₂O₄ . 2H₂O), Anhydrous sodium carbonate (Na₂CO₃)

What is a standard solution?

Concentration is precisely known
Prepared by dissolving a primary standard in a specific volume of solvent

What is a standardised solution?

Concentration is accurately determined by titrating against a primary standard

Label the parts of the tritration equipment and how it works (method)

What will the pH curve look like for a strong acid and a strong base?

correct

What will the pH curve look like for a strong acid and a weak base?

Correct

What will the pH curve look like for a weak acid and a strong base?

correct

What is the end point?

The point the indicator changes colour in a titration

*It is the whole bar*

What is the equivalence point?

When the titrants are equivalent to the stoichiometric amount

When should the indicator Bromothymol Blue be used?

Strong acid and Strong base

Because the equivalence point is around 7

Because it is a neutral salt

When should the indicator Methyl Orange be used?

Strong acid and Weak base

Because the equivalence point is around 4

Because it is an acidic salt

When should the indicator Phenolphthalein be used?

Weak acid and Strong base

Because the equivalence point is around 10
Because it is a basic salt

What are random errors?

Small fluctuations of positive and negative direction of the experimental value away from the theoretical value

Examples of random errors

Judging the endpoint

Reading the starting volume of burette

How to minimise a random error?

Take multiple trials

What are systematic errors?

Consistent deviations in the same direction of the experimental value away from the theoretical value

Examples of systematic errors

Not taring scales

Wrong indicator choice

How to minimise a systematic error?

Use calibrated equipment

Special systematic error

The indicator is a weak acid so you need more hydroxide to neutralise

What is a indicator usually?

A weak acid

What is the indicator equation?

HIn + H₂O → In^- + H₃O⁺

When answering questions on indicator choice what to include?

• Name of salt

• Strength of acids

• Acidity of salt

• equivalence point, end point

• hydrolysis equation

• indicator choice

• colour change

What is an aliquot?

A small sample of a larger whole

What is an analyte?

A substance whose chemical components are being identified and measured

What is a titrant?

A solution of known concentration that is added (titrated) to another solution

What is a titre?

The strength of a solution or the concentration of a substance in solution

What is a concordant titrant?

Titrant volumes which results are 0.1ml apart

When titrating A against B what is known and unknown?

Solution A is placed in the flask and is known

Solution B is placed in the burette and is unknown

Strong acids

Hydrochloric acid, Sulfuric acid, nitric acid

Method

1. Rinse

2. pipette

3. indicator

4. burette

5. Titrate

6. trials

Methyl orange colours

red acid

yellow base

Bromothymol blue colours

yellow acid

blue base

Accuracy

how close a measured value is to the true value

Precision

The more closely a set of measurements agree with each other