Chem Practical 1 Finding The Concentration Of HCL in Solution Flashcards
State method to find the concentration of a solution of HCL
Wash the 250 cm³ volumetric flask with distilled water.
Use a pipette to transfer 25.0 cm³ of hydrochloric acid into the flask and dilute it to the mark with deionized water.
Prepare for titration: fill the burette with sodium hydroxide solution and place the diluted HCl in a conical flask with 2 drops of phenolphthalein indicator.
Add sodium hydroxide from the burette to the conical flask slowly, swirling until the pink color just fades.
Repeat titration until two concordant titres (within 0.05 cm³) are obtained
Use mean titre and concentration to get moles of NAOH then use balanced equation to obtain moles of HCL ,we have the volume of HCL (25cm3) now we can get concentration
Safety precautions for finding the concentration of HCL
Wear eye protection, as phenolphthalein is flammable and hydrochloric acid is an irritant.
Why is it important to have a titre around 25 cm³ rather than 10 cm³?
Larger titres reduce percentage error in measurements.
What is the role of phenolphthalein in this experiment
It acts as an indicator, turning pink in alkaline conditions and colorless in acidic conditions.
Explain how CO₂ in the air could affect results
CO₂ reacts with sodium hydroxide to form sodium carbonate, reducing its concentration and leading to an inaccurate titre.
What is the purpose of the titration experiment?
Phenolphthalein, an indicator, is added to the acid to signal the endpoint of the reaction. Initially, the solution remains colorless because it is acidic. As NaOH is slowly added, the acid is neutralized, and the solution will briefly turn pink (alkaline) before the color fades completely when neutralization is complete. The volume of NaOH (titre) needed to neutralize the HCl is measured. This data is then used to calculate the concentration of HCl using the balanced equation and formulas for moles and concentration.
How do you prepare 250 cm³ of a 0.0500 mol dm⁻³ solution of butanedioic acid?
Calculate the mass needed:
Mass
=
0.0500
×
0.250
×
118
=
1.475
g
Mass=0.0500×0.250×118=1.475g
Weigh 1.475 g of butanedioic acid.
Dissolve in ~100 cm³ distilled water in a beaker.
Transfer to a 250 cm³ volumetric flask using a funnel.
Rinse the beaker and funnel with distilled water.
Add distilled water to the flask until the meniscus reaches 250 cm³.
Stopper and invert the flask to mix thoroughly.
The titre was found for sodium hydroxide however it was inaccurate suggest why
Carbon dioxide reacted with sodium hydroxide forming sodium carbonate which decreases the concentration meaning titre recorded would be to large
