Calcium hydroxide (Ca(OH)
In water calcium hydroxide form alkali solution, although they are not very soluble. Hydroxides can react with acids to form salts. A neutralising effect is used by farmers when they put lime- calcium hydroxide- on their field to neutralise soil acidity. This is done as if the soil is too acidic, most crops will not grow well.
Hydrochloric acid (HCL)
Hydrochloric acid is a strong acid. Hydrochloric acid is used to break our food into smaller molecules in our stomach. As it is a strong acid it has a much higher electrical conductivity then a weak acid, as more ions are present. It can react with metals, alkali, metal oxides, and metal carbonate and all of the reactions involve h ions. A 0.1 mol dm solution of strong acid such as hydrochloric acid has a pH value of 1.
Method
- Get all equipment ready to use, clean out all equipment with distilled water:
- burette and burette stand
- pipette and pipette filler
- mini pipette’s
- volumetric flask
- conical flask
- distilled water
- hydrochloric acid
- limewater
- methyl orange indicator
- Set up burette stand with burette.
- Use a pipette filler and pipette to transfer 25cm of hydrochloric acid solution into a volumetric flask.
- Once it has been transferred to the 250cm volumetric flask, add distilled water up to 250cm so that the hydrochloric acid is diluted. Then transfer this diluted solution via the funnel to fill up the burette to 50cm ready to use.
- Then use pipette filler and pipette to transfer 25cm of limewater containing calcium hydroxide to a 250 conical flask.
- Then using a mini pipette add 3 drops of methyl orange indicator to the conical flask containing the limewater.
- Then place the conical flask with a glass tile underneath it to see visible colour change under the burette.
- Then slowly add in small quantities or drop by drop from the burette the hydrochloric acid solution from the burette until the indicator shows a change to a permanent pink colour.
- This is the end point of the titration.
- Record your reading on the burette as a rough one, then repeat 3 times and record results in a table.
How to dilute and why to dilute:
The hydrochloric acid has to be diluted in order for it to react effectively with calcium hydroxide. This is due to the concentration and volume of hydrochloric acid being too much so has to be diluted to become less. This can be done by diluting it with distilled water in a volumetric flask as 25cm will be filled will HCL and the rest 225cm with distilled water up top the 250cm mark.
Number of titration’s:
First a rough titration will be done. The three more titrations will follow. These will be recorded in a table. The initial titration and average titration value will be calculated.
Accuracy:
When doing any titration you have to be very accurate in order to achieve the effective results. You must strictly follow out all instructions very carefully and measure all solutions out accurately. As if you make the hydrochloric acid too concentrated this can effect your titration results.
Suitability:
This is a very suitable and effective way to do and calculate a titration as is done this way all the time. It can show effective colour change.
Risk assessment:
Safety:
Safety is very important when carrying out any practical experiment in the lab. Many general rules need to be followed in order to make sure we carry out our practical safely
General rules:
- Wear goggles at all time during the practical.
- Wear lab coats to protect clothing.
- If needed wear gloves.
- Tie long hair back
- Handle all glass equipment with care.
Solutions:
Calcium Hydroxide in lime water
CORROSIVE = causes burns. Irritating to eyes, skin and respiratory system so do not inhale.
With water = the reaction with water is vigorous and generate heat.
Hydrochloric Acid
May cause burns. The vapour is very irritating to the respiratory system.
Indicator
Not really as harmful as other solutions but if any of the above happen take the same protection advice as above.
Less harmful when put into diluted solution.
Indicator going to use is methyl orange.
Equipment List
All the equipment that will be needed to carry out this practical experiment.
ANALYSISING EVIDENCE AND DRAWING CONCLUSION:
RESULTS:
Average titration = 20+20+21=61
61 by 3 = 20.3
Calculating of diluted acid
Hydrochloric acid has to be diluted in order for it to react effectively with limewater.
25cm = o.3 mol dm
It is diluted to 250 so then the concentration of the diluted hydrochloric acid becomes 0.03 mol dm
Calculate the concentration of limewater solution:
It takes 25cm of 0.03 of hydrochloric acid to nentralise 35 of calcium hydroxide.
Step1
Ca (OH) + 2HCL Cacl + 2H O
Show how 1 mole of Ca(OH) reacts with 2 moles of hydrochloric acid.
Step 2
Find out how many moles of hydrochloric acid were used.
We use 25cm of 0.03 mol dm of HCL.
In 1cm of the solution we would have 0.03
- x 30 moles of HCL
MOLES OF HCL
Number of moles in a solution = concentration x volume of solution in cm
1000
= 0.3 x 25cm
- = 7.5 for 1 mole
In the balanced equation there is 4 moles of HCL which equals 7.5 x 4 = 30 moles
step 3
30
25 x 30 moles = 0.36
The concentration of calcium hydroxide is 0.36 mol dm
EVALUATING EVIDENCE AND PROCESS ASSESMENT
RELIABILTY
On general terms the experiment is reasonably reliable but in any titration there are errors or uncertainties related to the precision of the equipment used.
The precision errors are as follows:
When a 25o volumetric flask is filled correctly the bottom of the menicus rests on the calibration. The error is o.2 cm 0r 0.08%.
Burette:
One drop from the burette has a volume of approximately 0.05cm. an error in one drop of 50cm = 0.4%
Pipette
When a 25cm pipette is used correctly it is allowed ti drain and retain the last drop. The error is 0.06cm or 0.24%.
Calculating the percentage error
Percentage error = error x 100
Reading
Volumetric flask
= 0.2 x 100
250 =0.08
Burette
= 0.4 x 100
50 = 0.8
Pipette
= o.o6 x 100
25 = 0.24
Procedural error can arise if your practical technique is not good. A good technique will involve:
Method can be improved by:
- the solution in the volumetric flask needs thorough mixing
- all equipment should be washed out using distilled water
- the end point of the titration can only be determined accurately if the solution from the burette is added drip by drop with swirling as the end point is reached.
- When an indicator is used in a titration only the minimum number of drops is added each time.
There was not really any anomalous result as all the 3 titration’s done has very close and similar readings
The titration was done 3 times to improve the reading of the experiment.
Any additional titration’s done after 3 times were not really necessary to ensure that the results were accurate.
The overall accuracy and reliability of the evidence that the experiment supplied is reasonably accurate as the 2 solution did react together well and a noticeable colour change from a pale orange to a permanent pink was visible.
Due to the percentage error in the experiment technique is could have resulted in maybe the readings being slightly lower then they really should have been.
Coursework
Solubility of calcium hydroxide
By Sabina fareed
Reference
chemical ideas book
Chemistry for you by lawrie ryan
Chemical ideas work sheets