Safety
- Lab coat
- Goggles
- Hair tied back
Hazards
Chemical risk
Hydrochloric acid it very corrosive, wear eye protection and gloves. Use a fume cupboard because its vapour is very irritating to the respiration system. It also causes severe skin burn. If the solution is swallowed seek medical attention immediately, and if spilt on skin and clothes remove clothing and wipe liquid off skin with a cloth also seek medical attention. It is dangerous to add water to acids, (hydrochloric acid) but since a low concentration is used, it is relatively safe.
Calcium hydroxide (limewater) is mildly corrosive, and long-term exposure can damage your skin. Make sure to wear your safety goggles at all times. Wear a lab apron to avoid staining your clothes.
Methyl orange indictor dust is irritant to the eye.
To titrate this volume would require accurate precision. To make the experiment easier. The concentration of the hydrochloric acid will be diluted. This will mean that the end-point will not come as quickly, which means that it is less likely to be over shot. If the 0.3moldm-3 hydrochloric acid was used to neutralise reaction it will causes the reaction to happen more quickly causing to produce an inaccurate end-point.
Equation Ca (OH)2 + 2HCl CaCl2 +2H2O
Ratio 1 : 2
This means that twice as many mole of hydrochloric acid are used to react with one mole of calcium hydroxide. This means that twice as much hydrochloric acid is needed to react with calcium hydroxide.
Making of a standard solution
I prepared a diluted HCl solution (0.03M) from concentrated HCl (0.3M). The reason is that concentration of Ca(OH)2 solution is approximately 0.015M, therefore a concentration of HCL should be the same magnitude. This how I calculated the necessary amount of water I added to the concentrated HCL.
The value of 0.03M HCL solutions is selected according to the stoichiometric reaction between the Ca(OH)2 and HCL:
Ca(OH)2 + 2HCL⇒ CaCl2 + 2H2O
1 mole⇔2moles
Therefore 1 mole of Ca(OH)2 reacts with 2 moles HCl, and since the concentration of Ca(OH)2 is about 0.015M, then the moles of HCl needed are equal to 2 ×0.015 = 0.03M HCl that is why I preparing a standard HCl solution of 0.03M.
From the equation above, we can state that the molar ratio between Calcium hydroxide and hydrochloric acid is 1:2
We can say that the concentration 0.3moldm-3 of hydrochloric acid is 20 times more concentrated than 0.015moldm-3 of calcium hydroxide, so the ratio is 1:20.
Ca(OH)2 + 2HCL⇒ CaCl2 + 2H2O
Mole: 1 : 2
Concentration provided: 0.015moldm-3 : 0.3moldm-3
Molar ratio: 1 : 20
Diluting the concentration of 0.3moldm-3 produces of ratio of 1:2
To achieve a concentration of 0.03moldm-3 hydrochloric acid, I will make the 0.3moldm-3 hydrochloric acid solution ten times more dilute.
Ca(OH)2 + HCL
New dilute concentration: 0.015moldm-3 : 0.03moldm-3
New molar ration: 1 : 2
The initial ratio between the diluted hydrochloric acid concentration 0.03moldm-3 and the concentrated hydrochloric acid of 0.3moldm-3 is 1:10
Concentration of HCl The New concentration of
Provided HCl
0.3M 0.03M
Molar Ratio 1 10
From these sets of result the new dilute concentration of hydrochloric acid is 0.03moldm-3 which will react with 0.015moldm-3 of Calcium hydroxide in a 1:2 ratio
When the concentration of the two solutions are equal the solution is neutralised, and produces a salt .It is this neutralised endpoint that is wanted in the experiment
Indicators are complex organic molecules, which are weak acid. Methyl orange is used when mixing a strong acid with a strong bases, phenolphthalein can also be used. However methyl orange has a pH which is acidic, which mean that when it is put in hydrochloric acid, it will turn red, this will be easy to see if enough indicator in the solution. Methyl orange indicator should have just turned form red to orange.
Methods
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Pour 50cm3 of 0.3M hydrochloric acid in a clean 100cm3 beaker, use this to clean the pipette and pipette filter with hydrochloric acid, by rotating the pipette and then empty the hydrochloric acid.
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Uses the clean pipette to extracted 25cm3 of hydrochloric acid from the beaker and pour it through a small funnel and into the 250cm3 volumetric flask.
- Rinse the beaker several times with distilled water, and then do the same with the funnel, to ensure that the beaker and funnel are clean and not contaminated.
- Add distilled water into the volumetric flask until it is just 1 cm below the graduation line. Then slowly using a clean dropping pipette add distilled water until the bottom of the meniscus is just touching the graduation line. Place a bung on top of the volumetric flask and shake vigorously, to ensure that the hydrochloric acid and the distilled water has mixed properly.
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Add a small amount of calcium hydroxide in the burette, rotate the burette at an acute angle, and empty the calcium hydroxide via the burette end and the jet. This cleans the burette and ensures that there is no contamination.
- Once cleaned, clamp the burette and fill the burette with 0.015M of calcium hydroxide. Run a little of the solution out of the burette into a beaker to make sure the jets is full of solution and also ensure that the jet consist of no bubbles, if there is any bubbles tap the side and wait for them to go down, and then closes the jet.
- Record the volume reading on the burette before starting the titration. Read the burette.
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Wash another pipette and pipette filter with hydrochloric acid by rotating the pipette and empty the hydrochloric acid. This will clean the pipette and will ensure that pipette is not contaminated.
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Use the cleaned pipette to withdraw 25cm3 of solution from the volumetric flask and transfer it to a conical flask. Allow the last drop to touch the conical flask, this ensures all hydrochloric acid is transfer to the conical flask.
- Add 5 drops of methyl orange, or until the red colour is visible. Make sure no more is added; otherwise the end result would be affected. You use methyl orange because you’re using a strong acid and strong base.
- Put the burette in the clamp stand and place a white tile underneath it and then the conical flask. The white tile will make it easier to see the colour change in the indicator.
- Record the volume reading on the burette at eye level before starting the titration. Add the calcium hydroxide to the conical flask in small volumes, swirling the flask after each addition to ensure that the two solution mix. The red colour will slowly change colour. The end-point of the titration is when the red colour first turns orange.
- Record the final reading and calculate the volume of solution you have run out into the flask.
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Your first attempt will be rough titration but it will give you a general idea of where the end- point comes. Do several more titration until you have three volumes, which agree, to the concordant region of 0.1cm3
- Rinse the conical flask twice with distilled water to ensure that all of the solution is out of the conical flask before the next experiment starts.
Improvements
Titration, itself must be repeated several times to build a more reliable set if results. Repeated set of results would increase the accuracy of the result.
White tile underneath the conical flask must be used to clearly see the colour change.
Conical flack should be washed out thoroughly with diluted water between titration, which has reacted with sulphuric acid
Read the burette along the level of the meniscus to make an accurate measure and more reliable results
Using white tile under the conical flask enables you to see clearly a colour change.
Colour observations should be made when looking at the colour in the conical flask
Bibliography
- Salter advanced chemistry chemical ideas, Heineman, second edition.
- Letts study guide A-Level chemistry
- Chemistry. The molecular nature of matter and change.
- A-level chemistry
- Search engine Yahoo
- www.studentcentral.com