13.3. To make up an approximate 0.1 M solution of sodium hydroxide, to standardise it (i.e. obtain the exact concentration) with a standard hydrochloric acid solution Flashcards
Why is it important not to allow solid sodium hydroxide to come in contact with your skin?
Solid sodium hydroxide is corrosive and causes severe burns.
How is it possible to standardise the NaOH in this experiment when the HCl is not a primary standard?
Even though the HCl is not a primary standard, the concentration of the solution is known from theprevious experiment, i.e. the HCl solution is a standard solution.
What is the purpose of the white tile under the burette during the titration?
The white tile enables us to detect colour changes more easily.
Why is the volumetric flask inverted several times?
To ensure that the solution is homogeneous, i.e. that the solution is the same concentration throughout.
Outline the correct precautions for using a pipette.
The main points:
- Rinse out the pipette with water to remove any impurities.
- Rinse out the pipette with the liquid it will contain so as to remove any drops of water.
- Fill the pipette using a pipette filler.
- Avoid bubbles of air entering the pipette when it is being filled.
- Ensure that the bottom of the meniscus is level with the graduation mark.
- Touch the tip of the pipette against the side of the flask when the discharge is complete.
- Do not blow out the liquid remaining in the tip of the pipette into the conical flask.
Draw a diagram to illustrate the shape of the meniscus of the HCl in the burette.
See Chemistry Live!, page 157, Fig 13.15.
If the two accurate titrations do not agree to within 0.1 cm3, what must be done?
If they do not agree, further titrations should be carried out until agreement to within 0.1 cm3 is obtained.
Why is the indicator left out when performing a titration to isolate a sample of the sodium chloride?
The indicator would contaminate the sample.
