Determining The Empirical Formula Of Lead Iodide Biology Essay

Background:

If lead is dissolved in azotic acid and so allowed to respond with K iodide, an indissoluble lead iodide compound is formed. The mass of iodide in the lead iodide compound can be calculated by subtracting the initial mass of lead from the mass of the precipitate. From the experimental informations one can cipher so the ratio of moles of lead to moles of I in the compound, and therefore find the empirical expression.

Variables:

Controlled

Mugwump

Dependant

Volume of azotic acid

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Determining The Empirical Formula Of Lead Iodide Biology
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Volume of K iodide solution

Volume of demineralized H2O

Mass of lead

Mass of the lead I compound

Method for Controling Variables:

In this experiment, the mass of lead was accurately weighed with a graduated electronic balance.

The volume of the azotic acid, dem. Water and K iodide solution was ever measured utilizing the same calibrated cylinder.

The mass of the lead iodide compound was ever determined on the same graduated electronic balance.

Materials:

Equipment:

3 pieces of 250 cm3 beakers ( each one labeled # 1, # 2 and # 3 )

3 ticker spectacless

6 Iron bases

3 Cartridge burners

Fume goon

3 pieces of Filter paper

3 pieces of Long-stemmed funnels

Electronic Balance ( 300 g, readability i‚± 0.

001 g )

10 cm3 Graduated Cylinder ( 0.2 cm3, step i‚± 0.1 cm3 )

20 cm3 Graduated Cylinder ( 0.5 cm3, step i‚± 0.1 cm3 )

100 cm3 Graduated Cylinder ( 1 cm3, step i‚± 0.5 cm3 )

150 cm3 Erlenmeyer flask

Ice bath

Chemicals:

0.130 – 0.150 gms Granulated Lead

3 ten 10 cm3 of 3 mol dm-3 Nitric Acid ( HNO3 )

1.2 g Potassium Iodide ( KI )

120 cm3 Distilled Water

Procedure:

About 0.130 – 0.150 g granulated lead was weighed accurately on an electronic balance in a 250 cm3 beaker glass ( labelled # 1 ) and its mass was recorded.

The procedure was repeated for the two other beakers labeled # 2 and # 3.

3 ten 10 cm3 of 3 mol dm-3 azotic acid, HNO3 solution was measured in a calibrated cylinder and poured onto each sample of lead in the beakers # 1, # 2 and # 3.

The beakers were covered with a ticker glass, and heated gently on an Fe base with a cartridge burner in a fume goon until the steam exited from under the ticker glass.

Reminder: Never boil it.

You may reheat it sporadically if a gas development Michigans.

After all of the lead was reacted, about 20 cm3 of distilled H2O was added to each beaker.

The solution was heated until it steamed.

The beaker was removed and set aside for several proceedingss.

Approximately 1.2 g K iodide, KI was weighed onto weighing paper and transferred to a 150 cm3 Erlenmeyer flask.

Then 60 cm3 of distilled H2O was added to each beaker.

The solution was heated until it steamed and so cooled down somewhat.

Then 20 cm3 of it was added easy while stirred into beaker 1.

The mixture was set aside to chill down for 5 proceedingss while the process was repeated with beakers 2 and 3.

To be able to turn the crystals in size, the precipitate was heated gently with changeless stirring for 5 – 10 proceedingss.

The mixture was cooled down utilizing an ice bath.

A piece of filter paper was weighed to the nearest 0.001 gm on an electronic balance ; its mass was recorded and was placed in a long-stemmed funnel.

Additional demineralized H2O was used to rinse the precipitate and it was wholly transferred from the beaker to the filter paper.

The filter paper was removed from the funnel and was placed on a labelled ticker glass and was allowed to dry for one hebdomad.

The filtration was repeated for the solids of tests 2 and 3.

Once the filter paper and solids for each tally are wholly dry, the filter paper and solids were weighed for each test on an electronic balance and the multitudes were recorded.

Data Collection

Raw Data:

Table 1: Measurements of the Masses of Lead, Filter Paper and Lead Iodine Compound

Beaker / Filter Paper #

1

2

3

Mass of Lead

/ g ±0.001 g

0.153 g

0.148 g

0.141 g

Mass of Filter Paper

/ g ±0.001 g

1.080 g

1.103 g

1.093 g

Mass of Filter Paper plus Lead Iodide

/ g ±0.001 g

1.383 g

1.404 g

1.375 g

Observations: After fade outing the lead in azotic acid a clear colorless solution was obtained. When adding the K iodine solution a xanthous crystalline precipitate formed.

Data Processing and Presentation:

Calculation of empirical expression test 1:

MASS OF LEAD IODINE:

Mass of filter paper plus lead iodide – Mass of Filter paper = Mass of Lead Iodide

FILTER PAPER # 1

1.383 g – 1.080 g = 0.303 g of Lead Iodide

Uncertainties

Balance: 0.001/1.383 * 100 = 0.072 %

Balance: 0.001/1.080 * 100 = 0.093 %

Entire uncertainness = 0.072 % + 0.093 % = 0.160 %

The mass of the lead I compound is 0.303 g ±0.16 %

MASS OF IODINE:

Mass of Lead iodide – Mass of Lead = Mass of Iodine

Trial # 1

0.303 g – 0.153 g = 0.150 g of Iodine

Uncertainties

Balance: 0.001/0.303 * 100 = 0.33 %

Uncertainty lead I compound = 0.16 %

Balance: 0.001/0.153 * 100 = 0.65 %

Entire uncertainness = 0.33 % 0.16 % + 0.65 % = 0.98 % 0.81 %

The mass of the I compound is 0.150 g ±0.98 % 0.81 %

Calculation of Moles of Lead ( Pb ) :

Trial # 1

n = m / M = 0.153 g / 207.19 g mol-1 = 0.000738 mol of Lead

Uncertainties

Balance: 0.001/0.153 * 100 = 0.65 %

Uncertainty of molar mass: 0.01 / 207.19 * 100 = 0.0048 %

Entire uncertainnesss = 0.65 % + 0.0048 % = 0.65 %

Gram molecules of lead = 7.38 ten 10-4 mol ±0.65 %

Calculation of Moles of Iodine ( I ) :

Trial # 1

n = m / M = 0.150 g / 126.90 g mol-1 = 0.00118 mol of Iodine

Uncertainties

Balance: 0.001/0.150 * 100 = 0.67 %

Gram molecules of lead = 1.18 ten 10-3 mol ±0.67 %

uncertainness of iodine = 0.81 %

uncertainness of molar mass = 0.01 / 126.90 * 100 = 0.0079 %

Entire uncertainnesss = 0.98 % + 0.0078 % = 0.99 %

Similar computations have been carried out for test # 2 and 3.

Ratio of Pb and I:

Ratio of Pb: I = 0.000711 mol: 0.00117 mol = 1.00: 1.64 = 1: 2

Table 2: Concluding consequence of the empirical expression computation

Test

Gram molecules lead

/ mol

Gram molecules Iodine

/ mol

Ratio

Lead to iodine

1

7.38 ten 10-4 ±0.65 %

1.18 ten 10-3 ±0.67 % 0.99 %

1: 1.60

2

7.14 ten 10-4 ±0.68 %

1.21 ten 10-3 ±0.65 % 0.85 %

1: 1.69

3

6.81 ten 10-4 ±0.71 %

1.11 ten 10-3 ±0.71 % 0.88 %

1: 1.63

Average

7.11 ten 10-4 ±0.68 %

1.17 ten 10-3 ±0.68 %

0.91 %

1: 1.64

Entire uncertainnesss: 0.68 % + 0.91 = 1.6 %

Percentage Mistake:

Theoretical Value – Experimental Value x 100 = Percentage Mistake

Theoretical Value

2.00 – 1.64 x 100 = 18 %

2.00

Decision and Evaluation:

In this experiment the empirical expression of a lead I compound was performed.

The mean ratio of lead to iodine obtained was 1: 1.64, and when rounded off would give a ratio of 1: 2 such that its divergence from the true value is 0.36 mol which chiefly depends on the oxidization position of lead.

The ground for the divergence of the consequence to the theoretical value is might be the pureness of the lead, a loss of lead compound, a spilling, or an mistake into how the measurings were taken.

Comparing the consequence of the per centum mistake to the consequence of the uncertainnesss of the measurings shows that there is a large difference into the per centum mistake which can non be explained. Conventionally, both values should be near to each other. Therefore the must hold be variability with the mistake in the measurings peculiarly the dross of the lead or the loss of lead throughout filtration.

The pureness of the lead has a large impact on the consequence of the experiment which once more is caused by a loss of a lead compound during filtration.

An betterment that could be done is to hold less spillage, mensurate the volume of chemicals more exactly.

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