Is Sulphuric Acid Dibasic?

In this plan I shall demonstrate that sulphuric acid is dibasic. In order to do this affectively I will plan experiment using scientific techniques. The experiment will involve titration. I will then validate these experiments using calculations and appropriate chemistry knowledge. The reactants I have selected that will neutralise sulphuric acid are shown below in the equations:

Reactants used in Titration and products obtained:

H2SO4 (aq) + 2NaOH (aq) –> Na2SO4 (aq) + 2H2O (l)

Background knowledge

The acid (sulphuric acid) is identified by being paired with a hydrogen ion and a base (sodium hydroxide) is identified by being paired with a hydroxide group. Sodium Hydroxide neutralises the sulphuric acid to form salt and water.

Sulphuric acid

A dibasic acid has two hydrogen atoms in its molecule which can be ionised. Sulphuric acid is dibasic acid, because it contains two hydrogen atoms which ionise in aqueous solution to become 2H+ ions. The equation below shows an ionic equation for sulphuric acid.

H2SO4 + 2H+ –> SO42-

Sodium Hydroxide

Sodium Hydroxide is used as a base. It is completely ionic, containing sodium ions and hydroxide ions. The hydroxide ions make sodium hydroxide a strong base which reacts with acid to form water and salt. The equations below shows a reaction between sodium hydroxide (base) with sulphuric acid (acid):

H2SO4 (aq) + 2NaOH (aq) –> Na2SO4 (aq) + 2H2O (l)

Ionic equation: 2H+(aq) + SO42-(aq) + 2Na+(aq) + 2OH-(aq) 2H2O(ll) + 2Na+(aq) + SO42-(aq)

Net ionic equation (only species that change): H+(aq) + OH-(aq) ? H2O(l)

Titration: How to carry out the experiment in the laboratory

Material used

* Sulphuric acid with a concentration of 1.00M.

* 50cm3 of 0.4M of sodium hydroxide that will be made up to 100cm3 with a concentration of 0.2M.

* Indicator

* Safety goggles

Diagram of apparatus and set up

Measuring cylinder

Burette

50cm3

Stand

Filtering Funnel

Pipette and a pipette filler

Volumetric flask 25cm3

Wash bottle of distilled water

White tile

Conical flask

250cm�

Beaker

Set up:

Safety precautions

Sulphuric acid

Sodium Hydroxide

Principal Hazard

Contact with the eyes or skin can cause serious permanent damage.

The 2M of solution of sodium hydroxide is used which is corrosive.

Safe handling

Always wear safety glasses. Do not allow the acid or a solution of it to come into contact with your skin.

Wear safety goggles and do not allow any of the solution to come into contact with eyes.

Emergency

Eye contacts: Wash the eye with plenty of water. Continue for at least 10 minutes and call for immediate medical help.

Skin contact: Wash off with plenty of water. Remove any contaminated clothing. If the skin reddens or appears damaged, call for medical aid.

If swallowed: Drink plenty of water and call for immediate medical help.

Eye contact: Wash the eyes with plenty of water. Continue for at least 10 minutes and call for immediate medical help.

Skin contact: Wash off with plenty of water. Remove any contaminated clothing. If the skin reddens or appears damaged, call for medical aid.

If swallowed: If the patient is conscious, wash out the mouth well with water. Do not try to induce vomiting. Call for immediate medical help.

Procedure

Preparing a standard solution of sodium hydroxide:

You measure accurately a sample of sodium hydroxide and use it to make a solution of concentration of 0.2M. This solution will be used to determine the volume of a solution of sulphuric acid.

Procedure 1

1. Measure 50cm3 of 0.4moldm-3 of solution of sodium hydroxide into a measuring cylinder.

2. Transfers the measured sodium hydroxide solution into the volumetric flask through the filter funnel. Rinse the measuring cylinder well, making sure all liquid goes into the volumetric flask.

3. Add water until the level is 1cm of the mark on the neck of the flask. Insert the stopper and shake to mix the content.

4. Using the drooping pipette, add enough water to bring the bottom of the meniscus to the mark, as in the diagram. Insert stopper and shake thoroughly ten times to ensure complete mixing. Simply inverting the flask once or twice does not mix the contents properly and may result in a fault.

5. Label the flask with sodium hydroxide (NaOH).

Procedure 2

In procedure 1 you made a standard solution of sodium hydroxide up to 100cm3.

To show when the reaction is complete-the Stoichiometry point or equivalence point an indicator called . The point at which the addition of one drop (or even less) of sodium hydroxide changes the solution form colourless to just is called the end-point and, in this case, shows that the reaction is just complete.

1. First fill the beaker with roughly 50cm3 of sulphuric acid.

2. Using the funnel rinse the burette with sulphuric acid solution and fill it with the same solution. It is important to rinse with the same solution as rinsing with water or other chemicals can cause contamination and therefore may affect the end point or the results. Record the initial burette reading in the ‘Trial’ column of Result Table.

3. Using the pipette filler, rinse the pipette with some of the sodium hydroxide solution, again this is to prevent any contamination. Carefully transfer 25.0cm3 of the solution to a clean 250 cm3 conical flask.

4. Add 2-3 drops of the indicator solution.

5. Run sulphuric acid solution forms the burette into the flask, with swirling, until the solution changes colour. The first flask may be used as a trail run, because you would probably over shoot the end-point. Record the final burette reading.

6. Refill the burette with the sulphuric acid solution, and again record the initial burette reading to the nearest 0.05cm3 (one drop).

7. Using the pipette, transfer 25.0cm3 of the sodium hydroxide to another clean conical flask. Add 2-3 drops of the indicator solution.

8. Carefully titrate this solution to end point, adding the acid drop by drop when you think the colour is about to change.

9. Repeat steps 5, 6 and 7 at least twice more.

Accuracy:

To obtain accurate results read the burette to the nearest 0.05cm3 (approximately one drop). Calculate the mean of the two (or preferably three) closest consecutive readings and quote this also to the nearest 0.05cm3. Note that this does not introduce a fourth figure; it merely makes the third figure more reliable.

Suitable quantities to use in both the experiment

In this experiment I have decide to use 50cm3 of 0.4M of sodium hydroxide which will be made up to 100cm3. The standard solution of sodium hydroxide will have 0.2M.

50cm3 of NaOH of 0.2M.

Moles = concentration x volume = 0.4×50 = 0.2

1000 1000

Specimen calculation

Titration data:

Conical flask reagent

Sodium hydroxide

0.2mol dm3

25cm3

Burette

reagent

Sulphuric acid

1.00mol dm3

Indicator

Trial run

Run 1

Run2

Burette reading

Final

28.0

25.5

24.5

Initial

0.00

0.00

0.00

Volume used (titre)/cm3

28.0

25.5

24.5

Mean titre/cm3

25.0

Step 1: Amount of NaOH = concentration x volume

Amount= 0.2moldm3 x 25.0 = 0.005mol

1000

Step 2: Amount of H2SO4 = concentration x volume

Amount= 1.00moldm3 x 25.0 = 0.025

1000

Step 3: Ratio of H2SO4 to NaOH

0.0025: 0.005

1 : 2

Ratio of H2SO4 to NaOH is 1:2

2 mol of NaOH reacts with 1 mol of H2SO4 so the equation is:

H2SO4 (aq) + 2NaOH (aq) –> Na2SO4 (aq) + 2H2O (l)

When this reaction occurs 1 mole of sulphuric acid releases 2 moles of hydrogen ions, hence proving that sulphuric acid is dibasic.