Apparatus
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25cm3 pipette
- Pipette filler
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50cm3 burette
- Burette clamp and stand
- Funnel
- White tile
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100cm3 conical flask
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100cm3 beaker
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250cm3 volumetric flask
- Calcium hydroxide
- Hydrochloric acid
- Methyl orange indicator
- Distilled water
Indicator
I am using methyl orange as the indicator for my titration because HCl and Ca(OH)2 are both strong acids, and by following the information sheet provided I know to use either methyl orange or phenolphthalein. I have chosen to use methyl orange over phenolphthalein because the endpoint will result in a colour change to orange, which is easy to notice.
Method
- The first step is to dilute the HCl solution as explained on the previous page. After adding 25cm to the conical flask, and adding distilled water until the meniscus is on the graduation mark, put a stopper in the flask and mix it vigorously.
- Wash out burette with distilled water and then with the HCl solution. Fill the burette with the HCl using a funnel and rush the jet through making sure no air bubbles are trapped.
- Then use a pipette and pipette filler to transfer 25cm of limewater into a washed conical flask and add 3 drops of methyl orange indicator.
- Place the conical on a white tile underneath the burette and record the reading on the burette ready to titrate.
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Whilst swirling the conical flask add the HCl from the burette to the Ca(OH)2 .
- Look for the end point, which will be a slight colour change to orange and then add drop by drop to ensure you do not go over the end point.
- When the end point is reached record the volume in the burette and subtract it from the initial volume to find the titre. Record this as a rough titration and repeat the experiment adding a few drops at a time as you become near to the endpoint.
- Repeat the experiment until you have three readings that agree to within 0.1cm of each other, recording the information in a table like the one below:
Record your titrations in a table like the one below:
Average Titre =
Accuracy
To maintain good accuracy throughout the titrations, the following steps should be followed:
- Washing the glassware out with the solutions that they will contain removes the remains of previous solutions and water drops. This makes sure there are no contaminants that will affect the concentrations of the solutions used.
- Removing the bubble from the jet of the burette prevents errors in the volume measurements.
- When measuring quantities of solutions filling so the bottom meniscus is at the level needed. This gives an accurate measurement of all quantities and prevents small anomalies in results.
- Using a white tile makes it easier to see a colour change so an accurate endpoint can be reached.
- Adding acid drop by drop when near the end point means that an exact endpoint can be reached.
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Repeating the titration until all results are within 0.1cm3 of each other makes sure that the endpoint found is correct and accurate.
- The burette readings are to 2 decimal places because this gives precise readings for the amount of titre so when calculating the concentration of the acid it will be accurate.
Percentage errors
Burette = 0.20%
Pipette = 0.24%
Flask = 0.08%
Total Percentage Error = 0.52%
Risk Assessment
Hydrochloric Acid
Corrosive and irritant. Wear eye protection and gloves. If substance gets in to eyes, mouth or on skin wash with water and seek medical attention.
Calcium Hydroxide
Corrosive and irritating to eyes. Wear eye protection and gloves. If hands are contaminated and the substance gets in to eyes or mouth, flood with excess water and seek medical attention.
Calcium Chloride
Irritant to eyes, skin and respiratory system. Is dangerous with water as it is an anhydrous salt and can cause water to boil. Wear eye protection and gloves. Use in a well ventilated area. If substance gets in to eyes, mouth or on skin then wash with water and seek medical attention.
Bibliography
Elements of life (Salters) – Titration experiment.
Chemical Ideas (Salters) – Concentration calculations.
Coursework Guidance – OCR.
