Neutralisation Coursework

Introduction

Neutralisation is the reaction of a base with an acid to form a neutral solution; which contains salt and water.

Acid + Base → Salt + Water

In my experiment I am trying to find out how much acid it takes to neutralise a base to form a neutral solution. I will use one molar of Nitric Acid as the acid and one molar of Ammonium Hydroxide as the base. So this will be a 1:1 ratio. (Molarity = how many molecules of the acid or alkali per 1000 cm3 (1 litre) of water.)

Nitric Acid + Ammonium Hydroxide → Ammonium Nitrate + Water

HNO + NH OH → NH NO + H O

Ionic bonding must take place to form the salt and the water. Ions have been formed because the original atoms have lost or gained electrons. These ions then have electrical charges because they do not have the same amount of positive protons and negative electrons. Atoms that loose electrons are called cations and have a positive charge. Atoms that have gained an electron and have a negative charge are called anions.

The General equation for making water is:

H + OH → H O

In this equation the Hydrogen ion has lost and electron and has become a cation with a positive charge. The Hydroxide ion has gained an electron and has become a negatively charged anion. Ionic bonds are created when ions combine in order to share and thus become electrically stable.

From the main neutralisation equation I have circled the parts to make water:

HNO + NH OH → NH NO + H O

Equipment

Ammonium Hydroxide – (base)

Nitric Acid – (acid)

Methyl Oxide - (to show the pH of the solution)

Clamp – (to hold the burette safely and securely in place)

Burette - (to hold the acid)

White Tile –

Funnel – (to pour the acid into the burette)

Goggles - (to protect the eyes)

Conical Flask – (to hold the base)

Measuring Cylinder – (to measure out the acid and the base)

Preliminary

Before we began our practical our teacher performed the experiment as an example to our class. The teacher set up the equipment as shown above. She informed us of the safety precautions and then began the experiment. She used 20ml of Ammonium Hydroxide (base), placing that in the conical flask. Then she added 6 drops of Methyl Orange (indicator). From the Burette she added 12ml of Nitric acid and swilled the conical flask. After this point she decided to control the amount added to the base and indicator by using the burette. This was a precaution as to not go past the point of neutralisation. At 18ml the base started to change colour into a more of a pink solution, from this point on she added 0.2 ml at a time. After adding 19ml of the acid it had neutralised the base. But as this is past the point of neutralisation she took 0.2ml off the reading to get the exact result.

In the preliminary experiment it proved that it takes approximately the same amount of Acid to neutralise 20ml of a base. Showing that it is a 1: 1 ratio.

In our practical we chose to change a few of the amounts used by our teacher to suit our own experiment. For example we started with 15ml of the base Ammonium Hydroxide. We increased the amount of ammonium hydroxide each time by 5ml. We used drops of methyl Orange.

How to use a Burette

Before you start your experiment you should make sure your burette is completely clean ...

This is a preview of the whole essay

In the preliminary experiment it proved that it takes approximately the same amount of Acid to neutralise 20ml of a base. Showing that it is a 1: 1 ratio.

How to use a Burette

Before you start your experiment you should make sure your burette is completely clean as any substances left could cause an anomalous result:

Close the tap
Run some water into the top of the burette.
Swish the burette up and down, letting the water clean all of the inside of the burette.
Open the tap and let the water drain.
Repeat.

Method

Fix the burette into the clamp; make sure it is stable and upright.
Place the clamp and burette on the floor.
Close the tap and using the funnel run some of the acid into the top of the burette.
Place the clamp and burette back on the desk.
Place beaker underneath the burette.
Open the tap and drain the acid.
Repeat a few times.
Close the tap and fill the burette to just above the 0cm mark with Hydrochloric Acid.
Remove the funnel
Make sure there are no bubbles in the burette.
Slowly open the tap and let the acid run down to exactly on the 0cm mark. Close the tap.
Remove the beaker
Put the white tile underneath the burette.
Place the conical flask on top of the white tile.
Adjust the height of the burette so the tip is just above the lip of the conical flask.
Put 15ml of Ammonium Hydroxide (base) into the conical flask.
Add 6 drops of Methyl Orange (indicator) into the conical flask, swirl so it is mixed in.
Open the burette and allow 10ml of the nitric acid into the conical flask. Swirl it around.
If the base and indicator have not turned from orange to pink the add 1ml at a time of Nitric acid. This is called Stepped Addition.
Keep adding until the ammonium base has turned pink in colour.
Take the reading from the burette and take 0.2ml away to find the exact reason. (This is like in the preliminary – when the base and indicator turn pink this mean it has gone past the point of neutralisation and we want to find the exact amount needed to neutralise a base.)
Repeat this process with 15ml in total 3 times as to get an average reading.
Repeat the whole process off stepped addition but change the amount of the Ammonium Hydroxide (base) to 20ml.

Repeat again the stepped addition with 3 more volumes of Ammonium Hydroxide:- 25ml, 30ml, 35ml. (In total there should be 3 readings for each of the 5 volumes of Ammonium Hydroxide)

Prediction

I predict that when I use 15ml of Ammonium Hydroxide it will take 15ml of Nitric Acid to neutralise it because my preliminary experiment showed that it was a 1:1 ratio.

I predict that for Monoprotic Nitric Acid:

Concentration of Acid x Volume of Acid = Concentration of Alkali x Volume of Alkali

The amount of acid needed to neutralise an alkali =

(Molarity of Alkali x Volume of Alkali) Molarity of Acid

(MAl x VAl) MA

This is because Nitric acid is monoprotic, which means it is an acid, which forms one H+ ion from each acid molecule.

Safety

As this experiment uses potentially dangerous chemicals and acids there are many safety precautions we have to make sure we take:-

Always wear goggles at all times as the acid could enter the eye and cause damage.
Fill the burette on the floor. This is so the burette is not situated above your head, which could be dangerous dealing with acid.
To have a well ventilated room because Ammonium Hydroxide can burn the inside of your nose.
Never sniff the Ammonium hydroxide for the reason given above.
Be careful when carrying and working with the acid and base as they are both potential irritants.
If acid is spilt then quickly wash it off with water, as it is an irritant and could cause itching. If itching does occur go immediately to the science lad technician for advice.
Make sure clamp is not too tight as the burette could be under too much pressure and break. This is especially important as the burette is made out of glass.

Fair Test

To make my experiment as fair as possible and to prevent any anomalous results I am taking preventative measures such as:

Make sure all the equipment is fully clean and no residue is left from past experiments (as this could effect results).
Use the same amount of methyl orange (indicator).
Use acid from the same stock as it is mixed by the technicians and could be slightly different.
The temp in the room could affect the rates of reaction of the acid.
Take repeat the process 3 times for each volume and then average out the results to make sure it is a fair as possible.

Results

I took three reading of each volume and found the average so I could get a more accurate result.

Analysis

My results and graph showed that my prediction was correct. I predicted that when I used 15ml of NH OH it would take 15ml of HNO for neutralisation to take place. My graph supported this.

From my graph it is clear to see there is a general upward trend which shows that my prediction that the amount of acid taken to neutralise the alkali will be a 1:1 ratio. Although looking closely at my results I see that the amount of acid taken to neutralise the alkali wasn’t exactly the same. In my experiment slightly less acid was needed to neutralise the alkali solution.

This experiment has actually proved that the following is correct Nitric acid and ammonium hydroxide:

This equation is also true for all acids and all alkalis.

Evaluation

In this experiment I felt a lot could go wrong and there were a lot of inaccuracies. Many of the measurements will have been inaccurate, for example the pH of the solution, because we were using an indicator which is not as accurate as using a pH meter.

I had one anomalous result; this was when I used 20ml of ammonium hydroxide. This may have occurred because we may have used a different batch of acid or ammonium hydroxide. As well as the anomalous result, the graph showed that the readings were not exactly a 1:1 ratio – they we’re slightly different to the prediction. This occurred because of inaccuracies; the volume of alkali could have also been slightly inaccurate, as well as the volume of the Nitric acid. This could also have been due to washing the conical flask after every experiment, there could have been left over water in the bottom of the conical flask which would have therefore made the solution more neutral. If I were to do this experiment again I would ensure that the conical flask was dried after every time it was washed so that excess water was not present.

Another factor, which could have affected my results, was the temp of the room or the temp of the acid and the alkali.

In my experiment I repeated the process three times for each amount of ammonium hydroxide. Each set of results was very similar, generally not more than 2ml between each reading. This shows that my readings were not as accurate as they should be or could be when using a pH meter.

On my graph because 0ml of Nitric acid should neutralise 0ml of ammonium hydroxide, I decided to extend my line of best fit to see whether it passes through the origin, as it should in theory. I extrapolated my line of best fit and have indicated it by showing it as the red dotted line. This shows my data must be slightly inaccurate, as it doesn’t pass exactly through the origin; it passes very close to the origin.

I could have also used a data logger to record the pH of the solution over a period of time and got an exact reading straight onto the computer. This would have made my results even more accurate.

I think that to improve this experiment I should try using different acids to see if my prediction applies to all acids. I also think to develop my experiment I should try different combinations of acids and alkalis.

I could have also used a data logger to record the pH of the solution over a period of time and got an exact reading straight onto the computer. This would have made my results even more accurate.

Overall my results support my conclusion that the amount needed of Nitric acid to neutralise a certain amount of ammonium hydroxide would be equal (1:1 ratio).