chemistry report 1(copy)

8/4/2019 Chemistry Report 1(Copy)

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Results :

Dilution of KOHFinal burette reading / cm3Initial burette reading / cm3

455

Volume of KOH used / cm

3

40

Volume of pipette used = 25 cm3

Burette reading

Titration number RoughAccurate

1 2 3 Mean

Final reading / cm3 43.2 43 46.2 46135.2 = 45.07

3

Initial reading / cm3 22 22 25 2572 = 24

3

Volume of HCl used / cm3 21.2 21 21.2 2163.2 = 21.07

3

Summary :

25cm3 of the diluted potassium hydroxide solution required 21.07cm3 of thehydrochloric acid for complete reaction.

The result used to obtain the value of hydrochloric acid is calculated as the tablebelow :

Final reading / cm3

43+46.2+46

3

= 135.2

3

= 45.07

Initial reading / cm3

22+25+25

3

= 72

3

= 24

Volume of HCl used / cm3

21+21.2+21

3

= 63.2

3= 21.07


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The concentration of the hydrochloric acid used is 3.65 g dm-3.

Concentration of the hydrochloric acid = molarity(mol dm-3) x molar mass= 0.1 x (1+35.5)= 3.65 g dm-3

Calculation ;

1. Calculate the number of moles of potassium hydroxide in 1dm3 of diluted solution.

No of moles of HCl = MV1000

= 0.1 mol dm-3 x 21.07cm31000

= 0.002107 mol

No of moles of KOH = No of moles of HCl (mol)Volume of KOH (dm3)

= 0.00210725

1000= 0.008428 mol

2. Calculate the number of moles of potassium hydroxide in the original undiluted

solution.

No of moles of HCl = MV1000

= 0.1 mol dm-3 x 21.07cm31000

= 0.002107 mol

3. Calculate the mass of potassium hydroxide in 1dm3 of the original solution.

Mass of KOH = No of moles(mol) x molar mass= 0.002107 x (39.1+16+1)= 0.1182 g

4. Calculate the mass of the potassium ions, K+, in 1dm3 of the original solution.

Mass of K+ = No of moles(mol) x molar mass

= 0.002107 x 39.1= 0.08238 g

= 0.1182 g


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Discussion:

From the equation there is a 1:1 molar ratio between HCl and KOH. When

potassium hydroxide solution is added to hydrochloric acid solution, water and KCl

salt is produced. Based on the result, titrating 25.00cm3 of KOH solution requires

21.07cm3 of 0.1M of HCl. With this, the concentration of KOH can be calculated

based on the molar ratio between HCl and KOH at the equivalence point whereby

number of moles of HCl will be equal to the number of moles of KOH

.

As the volume of hydrochloric acid needed to neutralize potassium hydroxide

is unknown, an indicator is used to determine the end point of the neutralization, an

indicator is used, which is methyl orange. It changes from orange to red when the

solution is neutralized. So, the volume of hydrochloric acid needed can be determine

by observing the color change of the methyl orange. When the color change to red,

the addition of hydrochloric is stopped and the volume of acid is observed and

recorded.

Precaution:

When measuring the volume of hydrochloric acid and potassium hydroxide

solution by burette and pipette, eye level should be on the meniscus to prevent

parallax error. The burette and pipette should be rinsed with hydrochloric acid and

potassium hydroxide solution respectively to prevent diluting of acid and alkali when

being measured. Distilled water is added slowly to the volumetric flask when near

calibration mark to prevent the addition of excess distilled water.


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Conclusion :

Reference :

1.

chemistry report 1(copy)

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