Alex T. ZhaoGregg KerrIB Chemistry HL 1BJanuary 16, 2013

Titration Lab

Part I: Preparation of Standard sodium carbonate solution.

Aim: To accurately prepare a primary standard of 0.5mol dm-3 sodium carbonate.

Equipment: Balance Volumetric flask (500 mL) Bunsen Desiccator Beaker (250 mL) Washbottle Storage bottle (approx. 500 mL) Distilled water Anhydrous sodium carbonate [Na2CO3] (4g)

Procedure:1. Calculate the mass of anhydrous Na2CO3

required to make up 500 mL of 0.05 mol dm-3 solution.

2. Heat a little more than the required amount to remove any water

3. Accurate weigh out into a beaker a mass of Na2CO3 approximately equal to that calculated but the mass must be known precisely so that the exact concentration can be calculated

4. Dissolve the solid in about 100 mL of distilled water5. Transfer this solution to a 500 mL volumetric flask. Rinse the beaker several

times with about 20 mL portions of distilled water, adding each washing to the volumetric flask

6. Make up the solution to precisely 500.0 mL with distilled water, adding the last few milliliters drop-wise from a washbottle.

7. Place the stopper in the volumetric flask and mix the solution thoroughly by repeatedly inverting the flask.

8. Transfer the solution to a clean storage bottle which should first be rinsed with a little of the Na2CO3 solution. Label the storage bottle with the type of solution and its date of preparation.

Processing of results, and questions:1. Amount of Na2CO3 used: 2.65 grams ± 0.01 grams

IB Chemistry HL Lab 6 January 16, 2013

Figure 1-Preparation of Sodium Carbonate

2. Some possible sources of inaccuracies may include:a. Not ALL the Na2CO3 is transferred to volumetric flask due to the

compound’s powdery natureb. Parallax error, resulting in slightly more/less than 500mL of solution

producedc. Inherent uncertainties of equipment used

Part II: Preparation and standardization of hydrochloric acid solution

Aim: (a) To make an approximate 0.1 mol dm-3 HCl solution and (b) to Standardize hydrochloric acid solution.

Equipment: Concentrated hydrochloric acid [HCl] (6mL) Graduated cylinder (10 mL) Volumetric flask (500 mL) Storage bottle (approx. 500 mL) Beakers (two 100 mL) Burette and stand Funnel Pipette (20 mL) Conical flask (250 mL) Standard sodium carbonate solution from Part I Methyl orange or bromophenol blue (a few drops) Distilled water

Setup:

Figure 2-Standardization of Hydrochloric Acid solution

Procedure (a): 1. Calculate the volume of concentrated HCl that would be required to prepare 500

mL of 0.1 mol dm-3 solution.

IB Chemistry HL Lab 6 January 16, 2013

2. Measure out this volume of concentrated HCl in a graduated cylinder and transfer to a 500 mL volumetric flask which is about half filled with distilled water. Make the solution up to the mark.

3. Mix well4. Transfer solution to storage bottle5. Label solution with concentration and date of preparation.

Procedure (b): 1. Place about 100 mL of the standard Na2CO3 solution into a clean beaker. If the

beaker is wet, rinse with a little of the solution first.2. Rinse a clean 25 ML pipette with some of the Na2CO3 solution. Pipette 25 mL of

the Na2CO3 solution. Add 2-3 drops of your chosen indicator to the flask.3. Place about 100 mL of HCl into a clean beaker. Again, if necessary, rinse the

beaker with a little of the solution first.4. Rinse a clean burette with some of the HCl and then fill the burette with the

solution5. Run a rough titration6. Record approx. volume of acid used.7. Run a few trials of accurate titrations8. Record accurate titrations

Data Collection:Amount of Hydrochloric Acid used

Rough Estimate

Accurate titrations

1 2 3 Avg.

Final Reading (mL) 28.2 27.32 27.54 27.46 27.44

Initial Reading (mL) 0 0 0 0 0

Titration volume (mL) 28.2 27.32 27.54 27.46 27.44

Processing of results, and questions:

1. Write the equation for the reaction:

a.2. Number of mols of Na2CO3 used:

a.3. Determine the number of moles of HCl which reacts with each mole of Na2CO3:

a. Ratio of Na2CO3 to HCl is 1:2, thus, 2*0.0125=0.025 mols of HCl is used in the titration.

4. Calculate the average volume of HCl used in the titrations. Use only those results that are reasonably consistent. From this determine the concentration of the HCl. Mark this information on the label of the storage bottle.

IB Chemistry HL Lab 6 January 16, 2013

a.5. Distinguish between the ‘equivalence point’ and the ‘end point’ of a titration.

a. The equivalence point is the point where the number of moles of the base used is equal to that of the acid. On the other hand, the end point is the point where the indicator being used changes color (also called 'indication point)'. 

6. In the “background” it was stated that the solution at the equivalence point is ‘somewhat acidic’. Explain why this is so.

a. This is because we are titrating a weak base with a strong acid7. Suppose that phenolphthalein, whose color change is in the vicinity of pH 9, had

been used instead of one of the indicators recommended.a. Would the volume of acid required for the titration be more or less than

that obtained?i. As we gradually add HCl to Na2CO3, the solution becomes more

acidic. Since solution with pH 9 is more basic than one with pH 3.5, less hydrochloric acid would be needed to change the pH value to 9 than to 3.5.

b. Would the calculated concentration of the HCl be higher or lower than the result obtained?

i. The concentration would be higher. Since C=n/V, when V decreases and ‘n’ remains the same, C increases.

PART C: Preparation and standardization of sodium hydroxide solution

Aim: Accurately determine the concentration of a sodium hydroxide solution.

Setup

IB Chemistry HL Lab 6 January 16, 2013Figure 3-Standardization of Sodium Hydroxide solution

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61: Conical flask holding Na2CO3 solution with indicator2: Na2CO3 solution ready to be used.3: HCl solution in Burette4: Ring stand5: Clamp6: Chul Ou

Data Collection:Amount of Hydrochloric Acid used:

Rough Estimate

Accurate titrations

1 2 3 Avg.

Final Reading (mL) 25.7 25.4 25.4 25.2 25.33

Initial Reading (mL) 0 0 0 0 0

Titration volume (mL) 25.7 25.4 25.4 25.2 25.33

Processing of results, and questions1. From the equation for the reaction, the volume of

NaOH used, and the volume and concentration of the standard HCl, calculate the concentration of the NaOH. Mark this on the label of the NaOH storage bottle

a. Equation:

Mole ratio of NaOH to HCl=1:1Thus,

2. What is meant by deliquescence? Why is a substance that is deliquescent unsuitable for use as a primary standard?

a. Deliquescence is a substance’s tendency to absorb moisture from the air. Thus, a substance that is deliquescent is unsuitable for use as a primary standard because it would absorb moisture from the air, causing its concentration to change constantly.

IB Chemistry HL Lab 6 January 16, 2013

Figure 4- One drop can change the color completely