Concentration of Hydrochloric Acid needed following dilution:
I will now work out the concentration of the hydrochloric acid needed to be the diluted value using the above information:
I have already been given the original concentration of the Hydrochloric acid which is 2.00 mol dm-3. Also, according to the balanced equation above, the ratio of Ca(OH)2 to HCl is 1:2. So, to make sure that 250 cm³ of calcium hydroxide can react with 250cm³ of diluted HCl, I can multiply the number of moles of calcium hydroxide by 2 (0.01×2) and be given 0.02 for the concentration of HCl that will be safe to use after dilution.
So, the new concentration for HCl is: 0.02 mol dm-3.
Volume of Hydrochloric Acid needed for dilution:
To work this out, I will need to use the following formula:
M1V1=M2V2
M1=Original Concentration
M2=New Concentration
V1=Volume to be Diluted
V2=New Volume
Using the above formula and the calculations worked out above, I am able to find out the volume of HCl to use in the volumetric flask to be diluted:
M1V1=M2V2
2×V1 = 0.02×250
= 0.02×250/2
V1 = 2.5cm³
So, the above calculations tell me that I am going to prepare 2.5cm³ of 2.00 mol dm-3 of HCl to be diluted with distilled water using the following apparatus and the following method.
Method
To Dilute the Hydrochloric Acid
List of Apparatus
· 25cm3 Graduated Pipette
· Pipette Safety Filler
· 250cm3 Distilled Water
· 250cm3 Volumetric Flask
· 2.5cm3 of HCl solution of concentration 2.00mol dm-3
· 250 cm³ Beaker
Method to dilute the Hydrochloric Acid
1) The first step is to transfer 2.5cm3 of the 2.00 mol dm-3 Hydrochloric Acid to the pipette using the pipette safety filler. When filling the pipette, make sure to measure at eye level to make sure that exactly 2.5cm3 of the acid has entered the pipette; the bottom of the meniscus is the level that the acid should be measured at.
2) Place the hydrochloric acid carefully into the volumetric flask using the pipette. Make sure that all of the acid is added.
3) Fill up the volumetric flask, containing the HCl, up to the 250cm3 mark making sure that it is exact. If it is not exact, the HCl will need to be prepared again. You should measure the solution at eye level to ensure accuracy.
4) Shake the flask gently but firmly to ensure that all of the HCl is evenly diluted with the distilled water.
5) Transfer all of the, now diluted, acid into the beaker. The 0.02 moldm-3 solution of HCl is now prepared and all apparatus used can be washed out and put to the side.
Method of Titration
List of Apparatus
· 25cm3 Graduated Pipette
· Pipette Safety Filler
· Burette
· Burette Clamp and Retort Stand (assembled correctly)
· Funnel
· Wash Bottle
· Phenolphthalein Indicator
· White Tile
· Two 250cm3 Conical Flasks
· Beaker containing the 250cm3 of 0.02 mol dm-3 HCl Solution
· Beaker containing the 250cm3 of Limewater with the Unknown Concentration (You must have enough solution to repeat the experiment 4 0r 5 times)
Method of Titration
Diagram:
Method:
1) Set up the apparatus as shown in the diagram making sure that the burette has been washed out with a small amount of the hydrochloric acid.
2) Fill up the burette carefully from the top with the diluted solution of the hydrochloric acid using a funnel. Allow a small amount of the HCl to run through the burette into the conical flask to ensure that there is no air lock. Make sure that you remove the funnel before the initial recording is taken down due to inaccurate results.
3) Using the wash bottle filled with distilled water, wash out both conical flasks thoroughly.
4) Using a small amount of the calcium hydroxide solution, make sure that the 25 cm3 pipette is rinsed out.
5) Place 25 cm3 of the calcium hydroxide accurately into the pipette and place this in one of the rinsed 250 cm3 conical flasks.
6) Repeat step 5 using another 25 cm3 of calcium hydroxide into the second conical flask.
7) Add 2-3 drops of methyl orange indicator to each of the conical flasks.
8) Record the initial burette reading at eye level, for accuracy, making sure that it is done to 2 decimal places. Open the burette tap and allow the hydrochloric acid to run down the burette and into the conical flask. Make sure that you swirl the conical flask as the acid is being added to the limewater until a permanent colour change has been observed. As methyl orange is being used, the colour change you should see is the solution going from orange to pink. Close the burette tap and record the colour change that you see.
9) Record the final reading. You have completed the trial recording and allow you to know approximately how much hydrochloric acid is needed to neutralise the calcium hydroxide. Using more hydrochloric acid, fill up the burette and record the initial reading once again. (This value does not have to be 0)
10) Repeat the steps above with the second conical flask, however, this time, stop adding the acid when the burette reads 3.00 cm3. Now, add the acid drop by drop before the trial, swirling and recording the volume which shows you the first permanent colour change.
11) This procedure should be repeated 4 or 5 times until consistent readings are given, that is ± 0.10 cm³. This could mean that up to 10 readings are taken.
Results Table
Once the experiment has been conducted, all of the results should be presented neatly in the following table:
Risk Assessment
Bibliography
· Essential AS Chemistry for OCR by Ted Lister and Janet Ranshaw. 2004 Edition and Year of Publication. Page 22. I used this book for reference towards balancing and constructing equations such as:
Ca(OH)2 (aq) + 2HCl (aq) CaCl2 (aq) + 2H2O (l)
· Letts Revise AS Chemistry by Rob Ritchie. Year of publication is 2000. Page35. I used this book when needing help for using the formula to find out the concentrations:
Concentration = Moles ×1000
Volume
· http://www.chemistry-react.org/go/Faq/Faq_8219.html. I used this website for reasons about using methyl orange as an indicator and about other possible indicators I could have chosen.
· http://en.wikipedia.org/wiki/Hydrochloric_acid. I used this website to help me with the risks involved with using hydrochloric acid and the safety methods in which to avoid its harmful qualities.
· http://www.scorecard.org/chemical-profiles/summary.tcl?edf_substance_id=1305-62-0. This website helped me to identify the risks with using calcium hydroxide and the safety precautions to take when handling the substance.
