Solutions, Dilutions and molarity calculations

Why is a conical flask, rather than a beaker, used in the experiment? – To allow easy mixing of solutions by swirling. 2. Why is the funnel removed from the burette after adding the acid solution? – so that the drops from the funnel will not fall into the burette. 3. In using a burette, why is it important to (a) rinse it with a little of the solution it is going to contain? – to remove any residual water and so avoid dilution of the acid solution when it is poured into the burette. (b) to clamp it vertically? – to enable the liquid level to be read correctly. ) to have the part below the tap full? – to ensure that the actual volume of liquid delivered into the flask is read correctly. 4. Give one reason for carrying out the following procedures during the titration. (i) The sides of the conical flask were washed down with deionised water? – To ensure that all of the acid added from the burette can react with the base. (ii) The conical flask was frequently swirled or shaken? – To ensure complete mixing of the reactants. 5. Why is a rough titration carried out? – To find the approximate end point.This nformation enables the subsequent titrations to be carried out more quickly. 6. Why is more than one accurate titration carried out? – To minimise error by getting accurate readings within 0. 1-3 cm of each other. 7. Explain why hydrochloric acid is not used as a primary standard? – The exact concentration of any hydrochloric acid solution is not known, unless it is prepared from standard ampoules. Laboratory grade hydrochloric acid is not sufficiently pure. 8. Can any of the following be used as primary standards: NaOH, H2S04, HN03? Explain your answer.A primary standard should be available in a highly pure state and stable. None of these substances are available pure because: (a) NaOH readily absorbs water and carbon dioxide from the air. (b) Concentrated H2S04 readily absorbs water from the ai r. (c)HN03 breaks down releasing N02 gas. 9. If you used only 10cm3 of sodium carbonate solution in the conical flask, calculate how much acid would be required to neutralise it. x 10-3 moles Na2C03 10cm3 Na 2CO 3 solution used at concentration of 0. 1 M 1 2 x 10-3 moles HCL required Concentration of HCL is 0. M 1000 x 2 x 10-3 / 0. 23crn3 required = 10. 5crn fi13. 10. Describe briefly how a pure dry sample of sodium chloride could be obtained having carried out the titration? – Using the information provided by the titration results, add Just enough hydrochloric acid to exactly neutralise 25cm 3 of sodium carbonate. The indicator should not be added. Gently heat the solution until all the water has evaporated to dryness. A sample of sodium chloride will remain in the beaker. Solutions, Dilutions and molarity calculations By AbigailHerbert