Titration of acid and alkaline

Chemistry AS coursework (titration)

Planning

The main task at hand is to find the concentration of a given volume acid. I am going to complete this task by using a method called titration. Titration is the process of finding the concentration of the given acid or base by neutralizing the solution using a known volume and concentration of alkaline or acid.

In this case I know that the concentration of the unknown acid will lie between 0.05 and 0.15 mole dmˉ³, so for my alkaline I am going to create a concentration of 0.1 mole dmˉ³. I have chosen this concentration because it is the average median of where the acid concentration could fall. To complete this titration I need to know when the solution will be neutralised, to know when the solution will be neutral I need to use an indicator. An indicator indicates when the solution reaches PH level 7; this is normally indicated by a colour change.

The acid that I will need to find the concentration of is sulphuric acid (H₂SO₄) and the alkaline that I will be able to control is sodium carbonate (Na₂CO₃). This indicator I am going to use needs to be strong acid based because I am using a strong acid (H₂SO₄) and a weak alkaline (Na₂CO₃), so I am going to use methyl orange.

Methyl orange is red as an acid and at alkaline is yellow, the problem that I have found is that there is not a big colour difference between red and yellows, so it may be hard to tell when the solution is neutral. There is a solution to this and this involves mixing xylene cyanol to the indicator this will then be *-------------* when in acid and *-------------* when in alkaline.

To complete this titration I will need to use the following equipment:

Beaker
Burette (50cm³)
Clamp stand
Conical flask
Digital balance (more accurate than analogue and can weigh within 0.01g)
Glass rod
Pipette
Volumetric flask (250cm³)

This is what the titration set up will look like:

Next I need to figure out how much volume of alkaline solution is sensible, because I don’t need a whole dmˉ³ (1 litre).First of all I need to see if the equation is balanced before I do anything, so:

Na₂Co₃ + H₂SO₄ = H₂O + CO₂ + Na₂SO₄

2x sodium ...

This is a preview of the whole essay

Beaker
Burette (50cm³)
Clamp stand
Conical flask
Digital balance (more accurate than analogue and can weigh within 0.01g)
Glass rod
Pipette
Volumetric flask (250cm³)

This is what the titration set up will look like:

Na₂Co₃ + H₂SO₄ = H₂O + CO₂ + Na₂SO₄

2x sodium 2x Sodium

Carbon Carbon

2x Hydrogen 2x Hydrogen

7x 0xygen 7x 0xygen

Sulphur Sulphur

As you can see that there is an equal amount of each atom on both sides of the equation, this means that the equation has a ratio of 1:1.

Now that I have found the ratio of the equation and made sure that the equation is balanced, I need to find the relative atomic mass of the alkaline, to do this I need to break down the alkaline I do this by taking the chemical Na₂Co₃ and saying: 2x (₁₁²³Na) 1x (₆¹²C) 3x (₈¹⁶O) = Na₂Co₃

To do this I add the atomic mass number e.g. ₁₁²³Na so......

2x (23) + (12) +3x (16) = 106g

Sodium carbonate (Na₂Co₃) is a solid so it needs to be dissolved into distilled water, in order to be titrated.

This 106g of sodium carbonate (Na₂Co₃) is equal to 1 mole. Now I need 0.1 mole so I need to divide this 106g by 10 which equals 10.6g. This 10.6g is per litre, but I don’t want a whole litre as this would just be wasting chemicals, I only need to have 250ml of the solution at 0.1 mole of sodium carbonate this will provide me with 5 tests and results, this is based on needing a full burette each time. Now that I have quartered the total volume I am going to have to quarter the amount of sodium carbonate that I put into the solution so 2.65g.

10.6g / 4 = 2.65g of Na₂Co₃

This means that for 250ml solution of sodium carbonate I need 2.65g of sodium carbonate powder. Once I have made the solution of sodium carbonate I should then be able to find the concentration of the sulphuric acid to do this I need to complete the titration. Once the titration has been complete I can then collect the results for example if 30cm³ of alkaline neutralised the 25cm³ of acid then I can find out the concentration of the acid. Because I know the concentration of the alkaline (0.1 mole per dmˉ³) I can find the acid but I need to find the concentration in 30 cm³. I do this by 30/1000 x 0.1 = 0.003 mole so in the 25 cm³ of acid there is 0.003 mole. To find the concentration in a litre 1000/25 = 40 so I need to 40 x 0.003 = 1.2 mole.

Method

To begin this titration I need to create my solution, I need to weigh 2.65g of anhydrous sodium carbonate I will do this by weighing a beaker and then weighing out 2.65g of anhydrous sodium carbonate into the beaker. To weigh the chemicals and the beaker I will use a digital balance that is capable of weighing within 0.01g, this is for increased accuracy. The contents of the beaker is then emptied into a another beaker and the beaker that has just been emptied is weighed again to see if a substantial amount of anhydrous sodium carbonate is left behind. If there is a substantial amount left behind then I will have to take this into consideration. The beaker that has now got the anhydrous sodium carbonate has a volume of distilled water added to it and it is stirred using a glass rod until the anhydrous sodium carbonate is completely dissolved into the solution. Once this is achieved I then will pour the solution into a volumetric flask. To pour any solutions I will use the glass rod to accurately pour the solution, this will happen because of water tension. The equipment, like the second beaker and glass rod will be rinsed of with distilled water to ensure that no sodium carbonate is left. In the volumetric flask I will add the distilled water until 250ml is reached. I know when this volume is reached because on the volumetric flask there is a measuring line and I fill until the bottom of the meniscus is level with this measuring line. I will use a pipette for more accuracy.

Measuring line

Now the volumetric flask should contain 250ml of sodium carbonate containing 0.1 moles per dmˉ³ concentration. Now I need to position a burette in a clamp stand. In this burette I will pour my sodium carbonate solution up to 50cm³ (full) for the first time because I don’t know how much of this solution is needed to neutralise the acid, once I find a rough amount then I will fill the burette to about 5 cm³ above that result e.g. it takes 25cm³ to neutralise the acid so I will fill the burette up to 30cm³. This is so that I don’t waste materials and because all burettes have a tolerance of accuracy, fuller the burette less accurate the solution volume will be. This may only be of 0.1cm³ but this is enough to make my results inaccurate. Into the 25cm³ sulphuric acid below the burette in the conical flask, I will add 2 to 3 drops of methyl orange and xylene cyanol, the solution should turn *________* in the acid but then when I open the tap on the burette I will release alkaline and slowly neutralise the solution and it should then change colour to *_________* when neutralised. I will repeat this until I have at least three similar results that are accurate.

Hazards and safety

Spillages should be cleaned to prevent accidents, any spillages of hazardous materials like acids and alkaline should be cleaned and if on the skin the skin should be rinsed of immediately. Goggles should be worn at all time in case of any breakages of glass or in case any acid or alkaline is splashed into the eye if this happens the eye should be rinsed as soon as possible.

Sulphuric acid (H₂SO₄) is a corrosive substance and should be cleaned with plenty of water if it comes into contact with eyes or skin. If ingested it can cause severe problems straight away and you should seek medical attention.

Sodium carbonate (Na₂Co₃) if inhaled may cause irritation to the respiratory tract. If it comes in contact with the skin it can cause irritation with redness again it should be rinsed with water. If alkaline comes in contact with the eyes it should be rinsed for about 10 minutes. Methyl orange should be treated the same as the acid and alkaline as explained as above.
Accuracy

Using a burette has a tolerance of 0.1 cm³ this means that if the burette is full then it could be out by 0.1 cm³ so if it’s full to 5cm³ then it could be inaccurate by 0.01 cm³. I will also use a white tile that I will place under the acid with the indicator in, to exaggerate the colour change this will help me see the change in colour and determine when the solution is neutralised. I should also make sure that everything that measure is to the bottom of the meniscus. To ensure there is no contamination I will rinse each piece of equipment and apparatus off with distilled water before use.