Find out how much acid there is in a solution

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AS Chemistry Coursework                              Name:  Mohammad Ahmed

                                                                         Candidate No. 9112

Planning

11. a) Identifies and defines a question or problem and devices a    

          practical procedure that is comprehensive and coherent to

          respond to the question or problem; describes fine detail

          about the procedure.

  • Aim

   

My aim is to find out how much acid there is in a solution. I have been provided with a sample of sulphuric acid solution which has a concentration between 0.05 and 0.15 mol dmˉ³. I will need to find its accurate concentration by carrying out a quantitative analysis known as titration.

  • What is titration?

A titration is a quantitative analysis which can allow you to determine the precise end-point of a reaction. This is when two solutions are reacted together. One solution of known concentration is placed in the burette. The second solution is placed in the conical flask. An indicator is involved depending on how strong or weak the acid or alkali is. The solution in the burette is run into the conical flask just enough until the reaction is complete. This can be indicated by the change in appearance of the solution.

  • Apparatus

  • Beaker(s)   (100cm³)
  • Balance
  • Spatula
  • Anhydrous Sodium Carbonate   (2.65g)
  • Distilled Water
  • Glass Rod
  • Funnel
  • Volumetric Flask   (250cm³)  (class B)
  • Rubber or Plastic bung
  • Burette     (class B)
  • White Tile
  • Small Funnel
  • Sulphuric Acid
  • Conical Flask     (250cm³)  (class B)
  • Pipette   (25ml)  (class B)
  • Pipette Filter
  • Methyl Orange Indicator
  • Lab Coat
  • Goggles
  • Gloves
  • Method

Making the Solution

  • Direct Weighing Version

  • Firstly, turn on the balance. Make sure the surface of the balance is clean.

  • Place the empty beaker on the balance and record it’s mass.

  • Press the Reset or Tare button. Now the balance should read zero.

  • Use the spatula to carefully add 2.65g of Sodium Carbonate into the beaker. To carry out this procedure correctly, take reasonable amounts of Sodium Carbonate and then gently tap the spatula onto the side of the beaker to remove any excess Sodium Carbonate.

  • When the reading is closer to the required value, use even smaller       quantities. This procedure will be helpful to accurately measure the Sodium Carbonate.

  • Now add some distilled water into the beaker to dissolve the Sodium Carbonate. Use the glass rod to crush large crystals until they become soluble. Add more distilled water if crystals are difficult to break.

  • Make sure that the Sodium Carbonate has been thoroughly dissolved into the distilled water. Then use the distilled water to rinse out the glass rod while still inside the beaker. This will clear away any leftover sodium Carbonate on the glass rod.

  • The Sodium Carbonate solution must be transferred from the 100ml beaker into a 250cm³ (class B) volumetric flask.

  • To do this accurately, place a funnel on top of the volumetric flask. Now carefully pour the Sodium Carbonate solution from the beaker into the volumetric flask. Hold the glass rod against the beaker for all of the solution to enter the volumetric flask and to prevent any spillage.

  • When all of the Sodium Carbonate solution is in the volumetric flask, rinse the glass rod with distilled water above the funnel to wash away any leftover Sodium Carbonate. Furthermore, add more distilled water into the volumetric flask until reaching the graduation mark. Put the plastic or rubber bung on top and make sure its securely fastened to prevent any spillage.

  • Now turn the volumetric flask upside down at an angle of 90° and bringing it back up with a smooth motion several times, to thoroughly mix the Sodium Carbonate solution.

Measuring the Solution

  • The Sodium Carbonate solution in the volumetric flask will be measured to the required volume and will be carried out for the process of titration.

  • I will be using a pipette filter and a 25ml pipette to remove the Sodium Carbonate solution from the volumetric flask.

  • I will carefully insert the pipette which will be attached at the bottom end of the pipette filter. By giving a slight twist and a push, the pipette will be firmly secured in place.

  • The pipette should contain Sodium Carbonate solution, 3ml greater than the required volume of 25ml.

  • The pipette filter will be removed with care after a slight twist and immediately the index finger will be placed on top of the pipette to prevent the solution from falling below the graduation mark.

  • To allow this solution to reach the graduation mark the index finger must be gently rubbed from side to side or top to bottom on the pipette.

  • When the solution reaches the graduation mark which can be recognized by looking at the meniscus, the solution can be transferred from the pipette into a conical flask.

  • The conical flask must be cleaned and rinsed with distilled water.

  • The conical flask must be placed right next to the volumetric flask from which the solution was taken. This will reduce the risk of any spillage.

  • Now let the solution of Sodium Carbonate from the pipette run into the conical flask until the last drop can be seen at the tip of the pipette.

  • Gently touch the tip of pipette onto the side of the conical flask for that last drop to come out.
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  • Add 10 drops of methyl orange indicator into the conical flask.

Cleaning the Apparatus

  • The burette itself must be cleaned with small quantities of distilled water.  The burette should be held in a horizontal position and the water must be swirled around, to remove any leftover liquid from previous experiments.

  • The distilled water should be drained from the burette through the open tap above a sink.

  • In addition to this, Sulphuric Acid must be used in small volumes and the same procedure should be applied to remove ...

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