Solutions, Dilutions and molarity calculations
Questions:
1. 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. (c) 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 information 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, H2SO4, HNO3? 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 H2SO4 readily absorbs water from the air. (c)HNO3 breaks down releasing NO2 gas.
1. 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. (c) 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 information 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, H2SO4, HNO3? 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 H2SO4 readily absorbs water from the air. (c)HNO3 breaks down releasing NO2 gas.