Required Practical 1 - titrations

A student devised an experiment to find the concentration of sulfuric acid in a sample of battery acid.

• A measuring cylinder was used to transfer 10 cm³ of battery acid to a volumetric flask.

• Distilled water was added to the volumetric flask until the volume reached 250 cm³

• A 25.0 cm³ sample of diluted acid was transferred from the volumetric flask to a conical flask using a pipette.

• A few drops of methyl orange indicator were added to the acid in the conical flask before titrating the acid with sodium hydroxide.

• The titration was repeated five times but concordant results were not obtained.

Which suggestion would improve the chances of obtaining concordant titres?

• Invert the volumetric flask several times after adding the distilled water.

• Wash the pipette with distilled water between each titration.

• Add extra drops of indicator to the sample when nearing the end point in each titration.

• Use a more concentrated solution of sodium hydroxide in the burette.

A student devised an experiment to find the concentration of sulfuric acid in a sample of battery acid.

• A measuring cylinder was used to transfer 10 cm³ of battery acid to a volumetric flask.

• Distilled water was added to the volumetric flask until the volume reached 250 cm³

• A 25.0 cm³ sample of diluted acid was transferred from the volumetric flask to a conical flask using a pipette.

• A few drops of methyl orange indicator were added to the acid in the conical flask before titrating the acid with sodium hydroxide.

• The titration was repeated five times but concordant results were not obtained.

Which suggestion about rinsing the conical flask between each titration would improve the accuracy of the titrations?

• Rinsing with acid.

• Rinsing with alkali.

• Rinsing with water.

• No rinsing with any liquid.

A student devised an experiment to find the concentration of sulfuric acid in a sample of battery acid.

• A measuring cylinder was used to transfer 10 cm³ of battery acid to a volumetric flask.

• Distilled water was added to the volumetric flask until the volume reached 250 cm³

• A 25.0 cm³ sample of diluted acid was transferred from the volumetric flask to a conical flask using a pipette.

• A few drops of methyl orange indicator were added to the acid in the conical flask before titrating the acid with sodium hydroxide.

• The titration was repeated five times but concordant results were not obtained.

Which suggestion would reduce the overall measurement uncertainty in the titration?

• Use less concentrated alkali in the burette.

• Use phenolphthalein indicator instead of methyl orange.

• Use smaller samples of the diluted acid in each titration.

• Begin each titration with the burette filled to the 0.00 cm3 mark.

A student devised an experiment to find the concentration of sulfuric acid in a sample of battery acid.

• A measuring cylinder was used to transfer 10 cm³ of battery acid to a volumetric flask.

• Distilled water was added to the volumetric flask until the volume reached 250 cm³

• A 25.0 cm³ sample of diluted acid was transferred from the volumetric flask to a conical flask using a pipette.

• A few drops of methyl orange indicator were added to the acid in the conical flask before titrating the acid with sodium hydroxide.

• The titration was repeated five times but concordant results were not obtained.

Which of these is important in ensuring that the student’s experiment is safe?

• Do the titration in a fume cupboard.

• Wear gloves when measuring out the battery acid.

• Wash hands before doing the titration.

• Carry the burette horizontally when collecting the apparatus.

25.0 cm³ samples of NaOH solution were taken by pipette from a beaker. These were then titrated with an aqueous solution of ethanoic acid. The concentration of ethanoic acid calculated from the experimental results was found to be lower than the actual value.

Which of these could explain the difference?

• Rinsing the pipette with distilled water before filling with NaOH

• Rinsing the burette with distilled water before filling with ethanoic acid

• Rinsing the walls of the conical flask with distilled water during the titration

• Rinsing the beaker with distilled water before filling with NaOH

What is the burette reading for this transparent liquid?

• 24.10 cm³

• 24.30 cm³

• 25.70 cm³

• 25.90 cm³

A volumetric flask was used to prepare 250 cm³ of a solution.

The solute was added from a plastic weighing container.

Weighing container with solute 10.13 g

Weighing container after solute added to volumetric flask 4.48 g

Each reading from the balance has an uncertainty of ±0.005 g

What is the percentage uncertainty in the mass of the solute used?

• 0.09%

• 0.11%

• 0.18%

• 0.22%

The maximum uncertainty when weighing 0.250 g on a balance was 0.001 g.

What is the percentage uncertainty?

• 4.0%

• 0.4%

• 0.8%

• 250%

Which of these pieces of apparatus has the lowest percentage uncertainty in the measurement shown?

• Volume of 25 cm³ measured with a burette with an uncertainty of ±0.1 cm³.

• Volume of 25 cm³ measured with a measuring cylinder with an uncertainty of ±0.5 cm³.

• Mass of 0.150 g measured with a balance with an uncertainty of ±0.001 g.

• Temperature change of 23.2 °C measured with a thermometer with an uncertainty of ±0.1 °C.

A student is provided with a 5.00 cm³ sample of 1.00 × 10⁻² mol dm⁻³ hydrochloric acid. The student is asked to devise a method to prepare a hydrochloric acid solution with a concentration of 5.00 × 10⁻⁴ mol dm⁻³ by diluting the sample with water.

Which of these is the correct volume of water that should be added?

• 45.0 cm³

• 95.0 cm³

• 100 cm³

• 995 cm³