Titration Lab Report - Ap0304 Practical Transferable Skills & Reaction Equations PDF

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AP0304 Practical and Transferable Skills

Date of Lab: 28/11/2016

INTRODUCTION A standard solution is a specific solution which has an accurate concentration and it is usually given in moldm-3.1 To make a good standard solution, it must have accurately measured chemical components which will increase certainty which will help with the determination of substances that have unknown concentrations. 2 The aim is to prepare a standard solution of sodium carbonate and then use it to determine the unknown strength of hydrochloric acid. Titration is a method of chemical analysis. It is used to determine the exact amount of a reactant in a flask by determining the exact endpoint of a reaction. In this experiment titration is used to determine the concentration of hydrochloric acid. After the volume of the acid used during the experiment is calculated, concentration can be found. Indicators are used to determine the endpoints of titration. An indicator changes colour due to the solutions acidity. Indicators that are used varies from titration to titration. Two indicators are used in this reaction because Phenolphthalein and Methyl Orange are used for this reaction because they cover two equivalence points. Two of them are used because the titration has two steps. The first point ranges from the pH 3 to 4 and Phenolphthalein ranges from 8 to 9.

REACTION EQUATIONS Step 1 – Phenolphthalein Titration: (Pink to Colourless) Na2CO3 (aq) + HCl (aq) → NaHCO3 (aq) + NaCl (aq) Sodium Carbonate (aq) + Hydrochloric Acid (aq) → Sodium Bicarbonate (aq) Sodium Chloride (aq)

Step 2 – Methyl Orange Titration: (Orange to Colourless) NaHCO3 (aq) + HCl (aq) → NaCl (aq) + CO2 (g) + H2O (l) Sodium Bicarbonate (aq) + Hydrochloric Acid (aq) → Sodium Chloride (aq) + Carbon Dioxide (g) + Water (l)

EQUIPMENT LIST      

250mL Beaker Glass Rod 250mL Volumetric flask Funnel Pipette Filler 25mL pipette

1 Creative Chemistry. Making standard Solutions. [ONLINE] Accessed at: http://www.creativechemistry.org.uk/alevel/module1/documents/N-ch1-49.pdf [07/12/16] 2 Study.com. Standard Solution: Definition & Method. [ONLINE] Accessed at: http://study.com/academy/lesson/standard-solution-definition-method.html [07/12/16]

AP0304 Practical and Transferable Skills

        

250mL Conical Flask Clamp Clamp Stand Burette White tile Weighing boat Scales Marker pen 2 x 5 pasture pipettes + rubber bulbs

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Distilled water Anhydrous Sodium Carbonate – Irritant Hydrochloric acid – Irritant Phenolphthalein – Flammable, toxic if swallowed Methyl orange – Flammable, toxic if swallowed

Date of Lab: 28/11/2016

METHODOLOGY Standard Solution First, safety googles had to be worn at all times to keep the anhydrous sodium carbonate away from the eyes. To begin with the balance was zeroed and then an empty weighing boat was placed onto the balance and 1.40g of anhydrous sodium carbonate was added and the combined mass of the weigh boat and anhydrous sodium carbonate was noted down (4.03). The sodium carbonate was then transferred into a 250ml beaker and the ‘empty’ weigh boat was reweighed and the mass of the remains on the weighing boat was recorded. The difference between them was the amount of anhydrous sodium carbonate used in the making up of the solution. 150ml of distilled water was then added to the beaker and was then stirred with a glass rod while swirling the solution until all the sodium carbonate had dissolved. The solution was then transferred into a 250ml volumetric flask using a funnel and it was inverted at least 7 times. Then the stirring rod and beaker were then thoroughly rinsed with further distilled water and the washings poured into the volumetric flask via the funnel and the funnel was then also rinsed with additional distilled water. Then deionised water was added to the solution until the base of the meniscus was touching the 250ml mark on the flask. The stopper was firmly placed onto the flask and it was then inverted 10 times to ensure the solution was thoroughly mixed. Finally, the flask was labelled sodium carbonate solution and the names of those conducting the experiment were also added.

TITRATION

AP0304 Practical and Transferable Skills

Date of Lab: 28/11/2016

Firstly, a pipette filler was used to transfer a 25ml aliquot of the sodium carbonate solution into a 250ml conical flask. 2-3 drops of phenolphthalein solution were added to the sodium carbonate solution. This solution was then titrated again hydrochloric acid. The solution was constantly swirled until it turned from pink to colourless. The titre was noted down in the results table and then 2-3 drops of methyl orange indicator was added the solution was once again titrated with hydrochloric acid and the solution colour changed from Orange to colourless which indicated the end of the titration. The titre was noted in the results table. This process was repeated 5 times.

RESULTS Measurement

(g)

Mass of weigh boat plus anhydrous sodium carbonate

4.03

Mass of weigh boat

2.63

Mass of anhydrous sodium carbonate in solution

1.40

Standard Solution Results Mass of anhydrous sodium carbonate 1.40g Mr of anhydrous sodium carbonate 105.988 Moles of anhydrous sodium carbonate = 1.40 ÷ 105.988 = 1.32x10 -2 mol Concentration of sodium carbonate solution = 1.32x10-2 / 0.25 = 5.28x10-2 moldm-3

Titration Results Phenolphthalein Titration Moles of sodium carbonate in 25ml aliquot = 5.28x10-2 x0.025 = 1.32x10-3 mol Therefore, moles of HCl is 1.32x10 -3 mol due to 1:1 ratio. n = cV ÷ 1000 therefore c = 1000n ÷ V So, concentration of HCl = (1.32x10 -3 x 1000) ÷ 18.23 = 0.0680 moldm-3 (3.s.f.) indicator – phenolphthalein

Rough

reading 1

reading 2

Reading 3

reading 4

final volume (cm3)

23.20

17.60

18.20

18.30

18.20

initial volume (cm3)

0.20

0.10

00.00

00.00

0.00

titre volume (cm3)

23.00

17.50

18.20

18.30

18.20

mean titre

18.23

AP0304 Practical and Transferable Skills

Date of Lab: 28/11/2016

Methyl Orange Titration indicator – methyl orange

Rough

reading 1

reading 2

reading 3

Reading 4

final volume (cm3)

37.40

35.80

36.20

36.10

36.30

initial volume (cm3)

23.20

17.60

18.20

18.30

18.20

titre volume (cm3)

14.20

18.20

18.00

17.70

18.10

mean titre

18.05

Number of moles of hydrochloric acid = 1.217118919x10-3 mol So, the concentration of HCl = (1.32x10 -3 x 1000) ÷ 18.05 = 0.0687 moldm -3 (3.s.f.)

DISCUSSION The values obtained are really close to the 0.075 that should have been obtained and also are really close to each other. The technique used during the titration is poor as % tries were made including the rough take to obtain concordant results.

CONCLUSION The titre values are different from each other by 0.001 but they are not same, so a mean must be taken which will be (0.0687+0.0680)/2=0.0684, 0.068moldm -3 (2.s.f.)...