Chemistry Project on Analysis of Fertilizers

Acknowledgment

I am grateful to Almighty for giving me the strength to successfully conduct my experiment and for sustaining my efforts which many a times did oscillate.

I am deeply indebted to Mr. O.J. Abraham sir, our chemistry faculty without whose constructive guidance this project would not have been a success. His valuable advice and suggestions for corrections, modifications and improvement did enhance the perfection in performing my job well.

I am obliged to Sr. Kiran our principal for providing the best of facilities and environment to bring out our innovation and spirit of inquiry through this venture.

I take special pleasure in acknowledging Mam Nirmala for her willingness in providing us with necessary lab equipment and constant support without which this effort would have been worthless.

I am grateful to My Parents and My Brother whose blessings and wishes have gone a long way in the completion of this arduous task.

Last but not the least I thank all My Friends and Batch Mates, without their prompt support my efforts would have been in vain.

SAUMYA GUPTA

CERTIFICATE

THIS IS TO CERTIFY THAT MISS SAUMYA GUPTA OF CLASS XII-SC HAS SUCCESSFULLY CARRIED OUT THE PROJECT ENTITLED “ANALYSIS ON FERTILIZERS” UNDER MY SUPERVISION.

ALL THE WORKS RELATED TO THE THESIS WAS DONE BY THE CANDIDATE HERSELF.

THE APPROACH TOWARDS THE SUBJECT HAS BEEN SINCERE AND SCIENTIFIC.

MRS. BEENA DASHORA CHEMISTRY FACULTY ST. MARY’S CONVENT SENIOR SECONDARY SCHOOL

Introduction

Definition

When light travels from one medium to another it changes the direction of its path at the interface of the two media. It is bending of a wave when it enters a medium where its speed is different.

Laws of Refraction

The incident ray, the refracted ray and the normal to the interface at the point of incidence, all lie in the same plane.
The ratio of the sine of the angle of incidence to the sine of angle of refraction is constant.

Bending Light

When a stick is submerged into water, the stick appears bent at the point it enters into water. This optical effect is due to refraction. As light passes from one transparent medium to another, it changes speed and it bends. How much this happens depends on the refractive index and the angle between the light ray and the line perpendicular (i.e. normal) to the surface separating the two mediums.

Index of Refraction (Refractive Index)

It is defined as the speed of light in vacuum divided by the speed of light in the medium.

It is represented by “µ” or “n”:

µ = C/V

C - Speed of light in vacuum
V - Speed of light in medium

It is also the degree or extent of deviation from its original path.

A ray of light travels along a straight line in a homogenous medium (meaning density is the same throughout). When it travels from one medium to another medium of different densities, the light deviates from its original path. The amount of deviation of light from its original path depends on the indices of refraction of the two media and is described quantitatively by Snell’s law.

Definitions

Angle of incidence - The angle that the incident ray makes with the normal is known as angle of incidence (“i”). Angle i = Angle AOB, where AO is the incident ray and OB is the normal.
Angle of refraction - The angle that the refracted ray makes with the normal is known as angle of refraction. Angle r = Angle COQ, where OQ is the refracted ray and OC is the normal.
Angle of emergence - The angle that the emergent ray makes with the normal is known as angle of emergence. Angle e = Angle SQR, where SQ is the emergent ray and RS is the normal.

Common Refractive Index

The values given are approximate and do not account for the small variation of index with light wavelength, which is called dispersion.

Medium	Refractive Index	Medium	Refractive Index
Vacuum	1.000	Ethyl alcohol	1.362
Air	1.000277	Glycerin	1.473
Water	1.33	Ice	1.310
Carbon disulphide	1.63	Polystyrene	1.59
Methylene iodide	1.74	Crown glass	1.50-1.62
Diamond	2.417	Flint glass	1.57-1.75

Snell’s Law

In 1621, a Dutch physicist named Willeboard Snell (1591-1626) derived the relationship between the different angles of light as it passes from one transparent medium to another. Snell’s law states that when light passes from one transparent medium to another, the speed of light changes and thus it deviates from its original path. The extent of deviation is given by the relation:

n1 sin θ1 = n2 sin θ2

n1 = Refractive index of medium 1
n2 = Refractive index of medium 2
θ1 = angle of incidence in medium 1
θ2 = angle of refraction in medium 2

Case I: Since n1 < n2, medium 1 is rarer than medium 2.

n1/n2 = sin θ2 / sin θ1

Since n1/n2 < 1, then sin θ1 / sin θ2 < 1, therefore sin θ1 > sin θ2.

Since 0 < θ < π/2, when sin θ1 > sin θ2, then θ1 > θ2.

Therefore the refracted ray bends towards the normal when it travels from a rarer to a denser medium.

Case II: Since n1 > n2:

n1/n2 = sin θ2 / sin θ1

Since n1 > n2, then n1/n2 > 1, therefore sin θ2 / sin θ1 > 1, and sin θ2 > sin θ1.

When 0 < θ < π/2, then θ2 > θ1.

Therefore the refracted ray bends away from the normal when it travels from a denser to a rarer medium.

Other Mathematical Relations for µ

Frequency is the characteristic of the source and remains unaffected when the medium changes. Let there be two mediums 1 and 2, where V1 is the velocity of light in medium 1, V2 is the velocity of light in medium 2, λ1 is the wavelength in medium 1, and λ2 is the wavelength in medium 2. Then V1 = nλ1, V2 = nλ2, and V1/V2 = λ1/λ2.
Refractive index of medium 1 with respect to medium 2 = n12. n12 = V2/V1; it is the ratio of velocity of light in medium 2 with respect to medium 1.
Refractive index of medium 1 with respect to medium 2, where medium 1 = water and medium 2 = air: air w.r.t. water: wµa = Apparent depth / Actual depth. Water w.r.t. air: aµw = Actual depth / Apparent depth.

Phenomena Due to Atmospheric Refraction

The sun is visible a little before the actual sunrise and a little after the actual sunset. By actual sunrise we mean the actual crossing of the horizon by the sun.
The apparent flattening of the sun at sunset and sunrise is also due to atmospheric refraction.

Total Internal Reflection

When light passes from an optically denser medium to a rarer medium at the interface, it is partly reflected back into the same medium and partly refracted into the second medium. This reflection is called internal reflection.

When a ray of light travels from denser to rarer medium, the ray deviates away from the normal. At a particular angle called the critical angle, the refracted ray just grazes or touches the surface, i.e. angle of refraction = 90°. The angle of incidence in the denser medium for which the angle of refraction in the rarer medium = 90° is called the critical angle.

If the angle of incidence is greater than the critical angle, the ray gets totally internally reflected.

Relation Between Refractive Index and Critical Angle

Consider a ray of light traveling from denser to rarer medium. Let ‘C’ be the critical angle. The angle of incidence i = C. Since angle of refraction = 90°:

Refractive index of air w.r.t. medium = sin i / sin r

mµa = sin C / sin 90°

mµa = sin C

sin C = 1 / aµm

Some Phenomena Due to Total Internal Reflection

Mirage: It is a phenomenon occurring in deserts. The ground air layer gets heated up and expands. Mirage is an optical illusion. The upper layer is denser as compared to the lower layer. The ground gets heated up very quickly; the lower layer of air expands and its density decreases. The ray of light traveling from the upper layers gets deviated away from the normal and suffers total internal reflection. The distant object appears to be inverted and to the observer a pool of water appears at a distant place. This phenomenon is called mirage.
Extra brilliance of diamonds: The refractive index of diamond is approximately 2.45. When a ray of light enters into diamond, multiple reflections take place inside due to total internal reflection, as µ = 1/sin C, giving C approximately 23° (very small).

Experiment

Aim: To determine the refractive index of water using a traveling microscope.

Apparatus: A coin, a beaker, a paper piece, traveling microscope.

Theory and Formula Used

Refraction is a phenomenon of propagation of light from one transparent medium into another medium such that light deviates from its original path. The ratio of velocity of light in the first medium to that in the second medium is called the refractive index of the second medium w.r.t. the first medium.

The bottom surface of a vessel containing a refracting liquid appears to be raised, such that apparent depth is less than the real depth. Refractive index of the refracting liquid is defined as the ratio of real depth to apparent depth.

µ = Real depth / Apparent depth

If:

r1 = reading of real depth of the coin (without water)
r2 = reading with water
r3 = reading at paper piece

Then:

Real depth = r3 - r1
Apparent depth = r3 - r2
µ = (r3 - r1) / (r3 - r2)

Procedure

For accurate measurements of length and depths, the compound microscope used is provided with a vernier scale which slides along with a main scale.
Note the number of divisions of vernier which coincide with the number of full main scale divisions.
Find the value of each main division and hence the least count of the microscope.
Move the microscope very gently. Using the screw, focus the eyepiece on the coin placed at the bottom of the empty container and bring the coin into focus. Note the reading of the microscope as r1.
Pour water into the beaker; the coin appears to be raised.
Move the microscope gradually and again bring the coin into focus. Record the reading as r2.
Put a piece of paper in the water and move the microscope upward until the paper comes into focus. Record the reading as r3.
The difference of r3 and r1 gives real depth; the difference of r3 and r2 gives apparent depth.
Record your observations and calculate the value of µ.

Observations

Least count of traveling microscope:

10 vernier scale divisions = 9 main scale divisions

50 V.S.D. = 49 M.S.D.

1 V.S.D. = ⁴⁹⁄₅₀ M.S.D.

L.C. = 1 M.S.D. - 1 V.S.D. = ¹⁄₅₀ M.S.D.

M.S.D. = ¹⁄₂₀ cm = 0.05 cm

L.C. = ¹⁄₅₀ x 0.05 = 0.001 cm

Reading of microscope focused on:

Reading	Coin without water M.S.R. (M) cm	Coin without water V. div coinciding (n)	r1 = M + n x L.C.	Coin with water M.S.R. (M) cm	Coin with water V. div coinciding (n)	r2 = M + n x L.C.	Paper in water M.S.R. (M) cm	Paper in water V. div coinciding (n)	r3 = M + n x L.C.
1.	5.2	5	5.205	5.9	40	5.940	8.15	12	8.162
2.	5.1	40	5.140	5.80	39	5.839	7.95	10	7.400
3.	5.05	20	5.070	5.75	36	5.789	8.00	20	8.020

Results

The refractive index of water as determined using the traveling microscope is 1.33.

Precautions

The least count of the scale of the traveling microscope should be calculated.
Once the microscope is focused on the coin, the focusing should not be disturbed throughout the experiment. Only the rack and pinion screw should be turned to move the microscope upward.
The eyepiece should be adjusted so that cross wires are distinctly seen.
The paper piece should be prevented from getting wet.

Elements

Nitrogen

Major fertilizers containing N:

(a) Ammonium nitrate (NH4NO3)
(b) Potassium nitrate (KNO3)
(d) Ammonium sulphate [(NH4)2SO4]

Preparation: Most nitrogen fertilizers are obtained from synthetic NH3. This chemical compound is used as a gas or in water solution, or it is converted to salts.

Nitrogen Deficiencies:

(a) Pale, green, yellow leaves
(b) Stunted growth

Nitrogen in Excess:

(a) Lower disease resistance
(b) Weakened stem
(d) Lower fruit quality

Phosphorus

Major fertilizers containing P:

(a) DAP - Diammonium phosphate [(NH4)2PO4]
(b) Ca3(PO4)2 - Calcium phosphate

Preparation: Most phosphoric fertilizers are obtained by the treatment of calcium phosphate with H2SO4. Calcium phosphate is mainly derived from phosphate rock and bones. Phosphate rock is found in deposits of sedimentary origin laid down on beds of the ocean floor.

Phosphorus Deficiencies:

(a) Pale purple colour on the underside of leaves
(b) Reduced flower, fruit and seed production

Advantages of P:

Encourages cell division
Hastens maturity, offsetting quick growth caused by N
Encourages root growth
Increases disease resistance

Phosphorus in Excess:

Causes dehydration of roots
Increases soluble salt content of medium

Potassium

Major fertilizers containing K:

Potassium chloride (Potash)
Potassium nitrate (KNO3)

Preparation: It is the seventh most abundant element found in the earth’s crust. Potassium chloride, which is the principal commercial form of potash, and some KNO3 are also used for production of potash fertilizer.

Potassium Deficiencies:

Leaves appear dry and scorched
Irregular yellow areas on the surface

Advantages of K:

Increases disease resistance
Encourages healthy roots and stems
Essential for starch formation
Efficient use of CO2

Potassium in Excess:

Affects soil acidity
Reduced flower, fruit and seed production

Analysis of Fertilizers

Fertilizer V (Vermi Compost)

No.	Experiment	Observation	Inference
1.	Take a pinch of fertilizer + few drops of dil. H2SO4	No reaction	Dil. group absent
2.	Take a pinch of fertilizer + few drops of conc. H2SO4	No reaction	Conc. group absent
3.	Take 1 ml of soda extract and acidify it with dil. HCl. Add few drops of BaCl2 soln. to it.	No reaction	Volatile group absent
4.	A pinch of fertilizer + few drops of NaOH soln. Heat it.	No reaction	Zero group absent
5.	Take 1 ml of O.S. (original solution) in a test tube and add few drops of dil. HCl	No reaction	1st group absent
6.	Take 1 ml of O.S. in a test tube, add few drops of dil. HCl. Warm the solution and pass H2S gas.	No reaction	2nd group absent
7.	Take 1 ml of O.S. in a test tube, add few drops of dil. HCl. Add few drops of conc. HNO3, heat it, cool it. Add a pinch of solid NH4Cl followed by excess of NH4OH.	No reaction	3rd group absent
8.	Take 1 ml of O.S. in a test tube, add few drops of dil. HCl. Add a pinch of solid NH4Cl followed by excess of NH4OH. Warm the solution and pass H2S gas.	No reaction	IV group absent
9.	Take 1 ml of O.S. + few drops of dil. HCl + a pinch of solid NH4Cl + 1 or 2 ml of (NH4)2CO3	White ppt	V group present; may be Ba2+, Sr2+ or Ca2+
10.	Filter the white precipitate, take a part of it, dissolve in minimum amount of CH3COOH. Add (NH4)2C2O4.	White ppt	Ca2+ confirmed.
11.	Flame test	Brick red flame	Ca2+ confirmed.

Result: Fertilizer has Ca2+ as cation. (The fertilizer detected is Vermi Compost.)

Reactions:

Ca2+(aq) + CO32-(aq) -> CaCO3(s)

2CH3COOH + CaCO3 -> Ca[CH3COO]2 + H2O + CO2

Ca2+(aq) + C2O42- -> CaC2O4(s)

Fertilizer III (Urea)

No.	Experiment	Observation	Inference
1.	Take 1 ml of Lassaigne Solution (L.S.) in a test tube and add few drops of freshly prepared ferrous sulphate solution. Heat it. Cool it. Add few drops of conc. H2SO4.	Prussian blue colour	Nitrogen present in elemental form.

Result: The given fertilizer has N in elemental form. (The fertilizer detected is Urea.)

Reaction:

O.C.N + Na -> NaCN

Chemistry Project on Analysis of Fertilizers