To determine the stoicheometric relationship between Sulfamic acid and Sodium Hydroxide in a neutralisation reaction, hence finding the bascity of Sulfamic acid.
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I predict that the ratio of moles of Sulfamic Acid and Sodium hydroxide will be 1:1 and they will react like this:-
When carrying out this practical wear safety glasses at all times.
When filling the burette hold the funnel slightly above the rim so as to break the seal allowing air to leave and fluid to replace it instead of the funnel filling up.
The above helps to prevent you over filling the burette and it spilling over. Always fill the burette after moving it lower down so that if it does spill over it does not pour onto you or into your eyes.
Wash your hands thoroughly after handling any Acids or Bases.
Do not rub your eyes or put your hands or fingers in your mouth at any point during the experiment.
Do not sit at the desk as this may prevent you moving in the event of a spillage.
>50 cm3 Burette.
>25 cm3 Pipette.
>250 cm3 Graduated flask.
>Boss clamp and Stand.
>Distilled water dispenser
>Solid Sulfamic Acid.
Part 1: creating Sulfamic Acid solution
>Place small beaker onto scales then zero/reset the scales.
>Measure between 2.500 and 3.00 grams of Solid Sulfamic Acid. (Record weight exactly)
>Tip Solid into 250 cm3 graduated flask, rinse the remaining solid into the flask with distilled water and a funnel.
>Rinse funnel and then neck of flask into the flask as well to ensure all of the solid enters the vessel.
>Fill with a beaker of distilled water and a funnel the flask to about 2 cm below the measuring line.
>Using the small pipette fill drop by drop holding the line at eye level until the bottom of the meniscus just touches the line.
>Put the stopper in and holding your thumb over the top of it shake until all of the solid dissolves and a clear liquid is formed.
Part 2:filing burette
>Make sure nozzle is closed and burette is clamped securely.
>Fill with NaOH to above the 0 point but below the top with a beaker and funnel.
>Remember to hold the funnel above the rim and to remove it afterwards.
>Place a waste beaker under the burette and open the tap to remove the bubble of air.
>Drain the burette slowly until the bottom of the meniscus just touches the 0 point line.
Part 3:the titration
>Using a 25 cm3 pipette and filler measure out 25 cm3 of Sulfamic Acid(aq).
>Drain this into a conical flask and rinse neck of flask with distilled water.
>Place the flask under the burette, set up as shown.
>First roughly titrate the solution with the Burette of NaOH measuring the start and end points.
>Refill the conical flask as before and the burette if necessary .
>Quickly add NaOH to within 2 cm3 of the rough titration.
>Continue to add more NaOH slowly whilst swirling until the small colour change begins to last for a second or two.
>Rinse and add NaOH one drop at a time until the colour change remains when swirled.
>Repeat until at least three accurate results are within 0.2 cm3 of each other.
I used 2.98 grams of Sulfamic Acid when making my solution and obtained the following results.
Sulfamic Acid is :-
Sodium Hydroxide is :-
When an acid and an alkali react together the general equation looks like this:-
ACID + ALKALI ï¿½ SALT + WATER
Acids donate H+ ions and the Hydrogen is replaced by the metal element of the Base. Bases donate an OH- which bonds to the H+ to form water (H2O).
This is shown below:-
Acid H+ Acid conjugate
Base OH- Base metal
The bascity of an Acid is however many H+ ions it gives off in a reaction or however in Sulfamic Acid (NH2SO3H) there is more than one Hydrogen that can be given off as a H+ ion, so the bascity is unknown.
It could give off any one, two, or three of the Hydrogen atoms dependant on its bascity. Its bascity is between 1 and 3 so there are three possible reactions which could take place.
A general formula for the reaction is:-
(n)NaOH + NH2SO3H ï¿½ NaNSO3H(3-n) + (n)H2O
(where (n) is the bascity of the acid)
The following three reactions could occur:-
1/ NaOH + NH2SO3H ï¿½ NaNSO3H2 + H2O bascity is 1 and ratio is 1:1
2/ 2NaOH + NH2SO3H ï¿½ NaNSO3H + 2H2O bascity is 2 and ratio 1:2
3/ 3NaOH + NH2SO3H ï¿½ NaNSO3 + 3H2O bascity is 3 and ratio is 1:3
I researched Sulfamic Acid on the internet and in textbooks and found that it is a mono-basic acid which has the following formula and structure:-
Sulfamic Acid is a Zwitterion, a molecule with two charges that counteract each other, the Nitrogen and Oxygen have a greater pull on the bond pair of electrons due to there high electro-negativity, this causes the bond to be polar, the Nitrogen and Oxygens draw the electrons closer and become slightly negative, the Hydrogens become positive because the negative electrons are further away. When an Acid releases a Hydrogen H+ ion the atom it was bonded too becomes negatively charged. All acid conjugates have a negative charge. Base’s release and OH- and this keeps the electron from the metal, so the Metal becomes positively charged. This is why the Metal bonds to the negative Atom on the acid conjugate.
When an Acid is in solution its Positive Hydrogen ions are released and these stick to Water, H2O, because it is another polar molecule, due to Hydrogen bonds. This forms a positive H3O+ molecule which then sticks to the Positive atom weakly in the acid conjugate. It is replaced by the much more positive charged basemetal ion when an alkali is added.
This is how I believe Sulfamic Acid and Sodium Hydroxide will react:-
Acid-Base indicators are dyes that are themselves weak acids and bases. However, the conjugate acid-base forms of the dye have different colours.
Different indicators change colour at different pH values not at neutral, pH 7, so in a neutralisation reaction it is important to choose an indicator which changes the right side of the Equivalence point (pH 7 in a neutralisation)
in this reaction a strong acid and a strong base are used and so the equivalence point is around pH 3 and so I will choose an indicator which has a definite change of colour near the equivalence point. Therefore I have chosen Methyl Orange. Shown below on the chart.
Using the following formula and the results I gain from titrating Sodium Hydroxide and Sulfamic Acid I hope to show that there is a 1:1 Stoicheometric relationship and hence that Sulfamic Acid is Mono-basic.
Ma x Va = Mb x Vb
NaOH is a Mono-base and so donates 1 OH- ion and so if the Sulfamic acid is Mono-basic then to neutralise each other there will be 1 Sodium Hydroxide molecule for every Sulfamic Acid molecule. To measure this reaction on a molecular level would be impossible and so we use Avagadro’s number.
Avagadro’s number is more commonly known as the mole. It is the number of C12 atoms in 12 g. This is 6.23×10 -23 atoms. By dividing the mass in grams of a substance by the Molecular mass Mr you will find the number of moles of that substance you have.
No of Moles = Mass(g) ï¿½ Mr
Molarity is the number of moles of a substance that is dissolved in 1 litre of water or a decimeter3.
Molarity = Moles(m) ï¿½ Vol (dm3)
Titration is the exact neutralisation of an Acid and a Base in order to find an Unknown (ie Molarity, No of moles etc). By using a Burette and an Acid Base indicator, an exact amount of reactant 1 can be added to a known amount of reactant 2 until a colour change of the indicator indicates the solution has become neutral.
The Molarity of the NaOH was measured to .001 mol/dm3.
The volume of NaOH added from the burette was measured accurate to 0.1cm3 at 20?C.
The Sulfamic Acid was measured with a pipette which measures 25cm3 at 20?C.
The mass of Sulfamic Acid solid measured was accurate to .001 grams.
The graduated flask measures 250 cm3 at 20?C.
When measuring liquids the meniscus must be taken into account, due to surface tension the surface within the pipette burette etc is curved. The meniscus is always lined up with the bottom touching the line and the line being held at eye level so that it is a solid line and not a cylinder like you would see if it was above or below eye level. This is why there is a continuous line around the glassware.
When using a burette so long as the meniscus is measured from the bottom at both the start and end point it will not effect the accuracy unlike in a pipette.
When filling the burette always remove the funnel because a drop of reagent could fall into the burette altering the start point.
When moving solids from one container to another or when adding liquids always wash with distilled water to make sure all of the substances enters the vessels.