A solution of hydrochloric acid was standardised by titration against a sodium carbonate solution using the following procedure.
- All glassware was rinsed correctly to remove possible contaminants.
- Hydrochloric acid was placed in the burette.
- 25.0 mL of sodium carbonate solution was pipetted into the conical flask.
The titration was performed and the hydrochloric acid was found to be 0.200 mol L¯1.
- Identify the substance used to rinse the conical flask and justify your answer. (2 marks)
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- Seashells contain a mixture of carbonate compounds. The standardised hydrochloric acid was used to determine the percentage by mass of carbonate in a seashell using the following procedure.
• A 0.145 g sample of the seashell was placed in a conical flask.
• 50.0 mL of the standardised hydrochloric acid was added to the conical flask.
• At the completion of the reaction, the mixture in the conical flask was titrated with 0.250 mol L¯1 sodium hydroxide.
- The volume of sodium hydroxide used in the titration was 29.5 mL.
- Calculate the percentage by mass of carbonate in the sample of the seashell. (4 marks)
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