To make 1000cm3 of a 0.100mol dm solution of sodium carbonate you would need 10.6g of the solid. So therefore to make 250cm3 of a 0.1mol dm solution of sodium carbonate, 2.65g was needed.
Into a weighing bottle 2.65g of solid anhydrous sodium carbonate was weighed accurately and the mass was then recorded. An analytical balance was used to weigh the solid because they are very accurate. A clean beaker was rinsed with distilled water and the solid was transferred from the weighing bottle into the beaker. The weighing bottle was rinsed three times with distilled water, transferring the washings each time. This was done to ensure that the entire solid goes into the beaker. Approximately 100cm3 of distilled water was added to the beaker. This was then stirred using a glass rod to dissolve the solid. The solution was then washed of the glass rod to ensure none is lost. The 250cm3 standard flask was washed three times and using a filter funnel the solution was carefully transferred in to it. The beaker and funnel was then rinsed several times making sure that all the solution has gone into the standard flask. Distilled water was then added until the solution was 1cm3 below the graduation mark. Using a dropping pipette enough water was added to bring the bottom of the meniscus up to the graduation mark. A stopper was added to the flask and inverted several times to help mix the contents.
Carrying out a titration
Once the solution was prepared the next procedure conducted was the titration. In this method measurements were taken carefully in order to accurately obtain precise results in the titration.
Preparing the burette
The burette was filled with distilled water; checks were made so that there were no leaks. Using a small funnel, 5-10cm3 of the prepared solution was added to the burette. The funnel was then removed. The burette was then taken from the stand and tipped and rotated to wash the inside surface with the solution. The solution was then placed into the waste beaker.
The burette was filled using a funnel with the prepared solution so the meniscus was above the zero mark. Accurate reading was taken by placing a white piece of paper behind the scale. The waste beaker was placed underneath the burette and the tap was opened until the solution filled the jet, it was made sure no air bubbles were present. The solution was then allowed slowly to run until the bottom of the line of the meniscus was on the zero mark.
A 25cm3 pipette was taken and rinsed with distilled water. A few cm3 of the prepared solution was drawn up using a pipette filler. The filler was then removed and tipped and rotated to wash the inside surface with the solution. The filler was replaced and the solution was drawn into the pipette until the meniscus was 2cm above the graduation
mark. Then carefully, the liquid level was allowed to fall until the bottom of the meniscus was just on the line. The liquid was poured down into a clean conical flask. When the movement of the meniscus stopped, there was a small amount of solution left in the tip of the pipette. Therefore, the tip was dipped below the surface of the liquid in the flask for 3 seconds
Performing a rough titration
In order to perform a rough titration a note of the burette reading was recorded to the nearest 0.05cm3. The conical flask was placed on a white tile under the burette. Three drops of indicator were added to the conical flask. Then from the burette the solution was added 1cm3 at a time, until there was a permanent colour change from orange to pink. This indicated the end point of the reaction. A note of the new burette reading was then recorded. To work out the volume of the solution added a calculation was made whereby the initial reading was subtracted from this end point value. The value calculated was the titre. The first titre was only a guide; therefore it was not included when the average value was calculated.
Performing an accurate titration
In order to perform an accurate titration, the whole titration method was carried out again. As the rough end point was approached, the solution was added a drop at a time and the flask was shaken. Each drop was added until one drop caused the colour to permanently change. The titration was repeated three times to get concordant results within 0.1cm3 of each other. Results obtained were recorded in a table format.
Results table
Risk assessment
Sulphuric Acid
Health Hazard Information:
Inhalation can cause damaging effects of the mucous membrane and on the upper respiratory tract. Sulphuric acid is corrosive and if swallowed it can cause severe burning of the mouth, throat and stomach. If it comes into contact with the skin it can cause redness and pain. Blurred vision can be a result if it comes into contact with the eye.
First Aid Procedures:
If inhaled, plenty of fresh air is needed. If breathing is affected medical help should be received immediately. Plenty of water should be given. If it comes into contact with the skin wash affected areas plenty of water, if irritation continues seek medical help.
If the eyes are affected wash with water and seek medical advice
Safety handling and personal precautions
Container should be labeled and the chemical should not be placed on a high shelf. The container should be kept tightly closed and stored in a cool, dry place. If spilt shut off all possible sources of ignition. In the event of a small spill neutralise the remaining with lime water or soda ash. All accidents should be reported to the lecturer. Laboratory coat, goggle and gloves should be worn.
Sodium Carbonate
Health Hazard Information:
Inhalation can cause respiratory problems and damage can be caused to the nasal septum due to inhalation of excess dust. Skin contact with the solid can cause irritation and redness. Symptoms of exposure may include burning sensation, coughing, shortness of breath, headache and vomiting.
First Aid Procedures:
If swallowed wash out mouth with plenty of water providing person is conscious. If inhaled, get fresh air. If breathing becomes difficult give oxygen and seek medical attention. In case of skin contact, wash affected area with plenty if water. Seek medical advice.
Safety handling and personal precautions:
Container should be kept closed and should be labeled. If spilt it should be swept, placed in a bag and disposed. Ventilate the area and wash the spill site after material pickup is complete
Methyl Orange:
Health Hazard Information:
If it is inhaled it can cause respiratory problems. Ingestion may cause irritation to the gastrointestinal tract. Symptoms such as coughing, sore throat and chest pains may occur. In contact with the skin, it can cause mild irritation and redness and mild irritation may be caused if the solution comes into contact with the eyes
First Aid Procedures:
If inhaled, fresh air should be received. If breathing becomes difficult medical attention should be given immediately. In the case of skin contact, it should be washed with plenty of water and medical attention should be received if irritation continues. In the event of the solution coming into contact with the eyes, the upper and lower eyelids should be lifted and the eye should be washed with water.
Safety handling and personal precautions:
Liquid should be kept in a closed container and stored in a cool, dry place. Protective equipment should be worn including safety goggles, gloves and laboratory coat.
Bibliography
-Technique sheet 1 making up a standard solution.
- Technique sheet 2 carrying out a titration.
- Advanced Level - Practical work for chemistry, Hunt A, Hodder and Stoughton 2004
- Advanced level – Practical work for chemistry, student guide, Parkinson J, Basil Blackwell LTD, 1991
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http://www.ocr.org.uk/OCR/WebSite/Data/Publication/Teacher%20Support%20&%20Coursework%20Guidance/AS_A_Level56421.pdf
