2.1 determination of concentration of HCl

what errors could occur during this experiment ?

• Some of the weighed NaHCO 3 may not be transferred from the weighing boat

• The colour change may not be clearly visible during the titration

How would you improve this experiment ?

• Place a white tile underneath the conical flask.

• Use the weighing by difference technique

what are some of the precautions you must take ?

• wear gloves

• wear googles

• handle glassware gently

what are the hazards within this experiment ?

• hydrochloric acid – causes severe skin burns and eye damage.

• methyl orange – toxic if swallowed.

why do we use a funnel ?

• safely and efficiently transfer the titrant solution into the narrow opening of the burette without spilling

why do we use a volumetric flask ?

• Precise Concentration

• Reduced Spillage

why do we rinse the beaker and glass rod with water and add it to the volumetric flask ?

• To ensure all the solute is transferred

Describe how you would make a standard solution ?

Weigh

2.10g

2.10g

of sodium hydrogencarbonate into a weighing boat then transfer to a

250cm3Add a small volume of distilled water to the beaker and stir until the solid completely dissolves.

• Transfer the solution to a

  250cm3

  250cm3

  volumetric flask using a funnel.

• Rinse the beaker and the glass rod with distilled water, adding the washings to the volumetric flask.

• Fill the volumetric flask up to the graduated line using distilled water.

• Stopper the flask and invert a few times to mix the solution

Describe how you would titrate the standard solution ?

Use a pipette and pipette filler to tran

of the standard

NaHCO3

NaHCO3

solution to a

250cm3

250cm3

conical flask.

• Add two or three drops of methyl orange to the flask.

• Fill the burette with hydrochloric acid (ensuring there is no air bubble) and record the initial burette reading.

• Add the hydrochloric acid from the burette to the conical flask until the end point is reached. Add the acid dropwise as you near the end point. At the end point, the solution will change from yellow to orange in colour.

• Record the final burette reading. The volume of

  HCl

  HCl

  added is the difference between the initial and final readings.

• Repeat until two concordant results are obtained.

what is a standard solution ?

a solution of known concentration

when transferring one solution to another beaker how would you ensure as much of the dissolved substance has been transferred ?

• rinse the glass rod and beaker with water and add to volumetric flask

what are three things required to take an accurate reading ?

1) Read at the bottom of the meniscus

2)Allow any reading on the wal of the biuret to settle before taking any readings

3)Ensure there are no air bubbles