# Chemistry projects on Analysis of Fertilizers

INDEX 1. INTRODUCTION

• Definition
• Laws of refraction
• Refractive index
• Snell’s law
• Mathematical relations
• Phenomenon
• Total internal reflection

2. EXPERIMENT:

• Aim
• Apparatus
• Procedure
• Results
• Precautions

3. BIBLIOGRAPHY

INTRODUCTION

(a) 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.

(b) Laws of refraction:

1. The incident ray, the refracted ray and the normal to the interface at the point of incidence, all lie in the same plane.
2. The ratio of the sine of the angle of incidence of 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 OR 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 straight line in a homogenous medium meaning density 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.

Diagram showing Refraction.

DEFINITIONS:

1. Angle of incidence – The angle that the incident ray makes with the normal is known as angle of incidence (“i“).

Ð i = Ð AOB

AO – Incident ray

OB – Normal

1. Angle of refraction – The angle that the refracted ray makes with the normal is known as angle of refraction. Ð r = Ð COQ

OQ – Refracted ray,

OC – Normal

1. Angle of emergence – The angle that the emergent ray makes with the normal is known as reemergence.

Ð e = Ð SQR

SQ – Emergent ray

RS – Normal

Common Refractive Index:

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

Table for refractive indices

## 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 speed of light changes and thus it deviates from its original path and extent of deviation is given by the relation-

n1 sin q1 = n2 sin q2

n1 = Refractive index of medium 1

n2 = Refractive index of medium 2

q1 = angle of incidence in medium 1

q2 = angle of refraction in medium

CASE I:

Since n1 < n2

Therefore medium 1 is rarer than medium 2

Therefore the relation

n1 / n2 = sin q2 / sin q1

n1/n2 is less than  1

sin q1 / sin q2 < 1

sin q1 > sin q2

Since 0 < q < p / 2     (when sin q1> sin q2)

q1 > q2

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

Case II :                       Since     n1> n2

Therefore by the relation

n1 / n2 = sin q2 / sin q1

Therefore   n1 > n2

n1 / n2 > 1

à    sin q2 / sin q1 > 1

à    sin q2 > sin q1

{When 0 < q < p / 2 }

q2 > q1

Therefore refracted ray bends away from the normal when it travels from denser to rarer medium.(For both cases refer to diagrams)

OTHER MATHEMATICAL RELATIONS FOR µ :

1. Frequency is the characteristics of the source and remains unaffected when the medium changes.

Let there be two mediums 1 and 2

V1= be the velocity of light in medium 1

V2 = be the velocity of light in medium 2

I1 = wavelength in medium 1

l2 = wavelength in medium 2

V1 = nl1

V2 = nl2

V1 / V2 = l1 / l2

1. Refractive index of medium 1 with respect to 2 = n12

n12 = V2 / V1 it is the ratio of velocity of light in medium 2 with respect to medium 1.

1. Refractive index of medium 1 with respect to medium 2

Medium 1 = water

Medium 2 = air

Air w.r.t. water wµa = Apparent depth / Actual depth

Water w.r.t to air aµw = Actual depth / Apparent depth

Refer to diagram

PHENOMENON DUE TO ATMOSPHERIC REFRACTION:

1. 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.
2. The apparent flattening of 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 deviate away from the normal. At a particular angle called critical angle the refracted ray just grazes or touches the surface i.e. Le of refraction = 90°. The angle of refraction in denser medium for which the Le of refraction in rarer medium = 90° is called critical angle.

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

RELATION BETWEEN REFRACTIVE INDEX AND CRITICAL ANGLE:

Consider that ray of light is traveling from denser to rarer medium. Let ‘C’ be the critical angle. The angle of incidence (i)

Ð i = LC

Since angle of refraction = 90°

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

mµa = Sin C / sin 90°

mµa= Sin C

Sin C = 1 / aµm

DIAGRAM

SOME PHENOMENON DUE TO TOTAL INTERNAL REFLECTION:

1. Mirage: It is 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 lower layer. The ground gets heated up very quickly the lower layer of air expands and density decreases. The ray of light traveling from the upper layers gets deviated away from normal and suffers total internal reflection and the distant object appears to be inverted and to the observer pool of water appears at a distant place and this phenomenon is called mirage.
2. Extra brilliance of diamonds : Refractive index of diamond is approx. 2.45 or 2.9 when a ray of light enters into diamond multiple reflection takes place inside due to TIR as µ = 1 / sin C, C approx. 23° (very small).

EXPERIMENT

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

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

Theory and Formula used:

Refraction is a phenomenon of propagation of light from one transparent medium into the other medium such that light deviate from its original path. The ratio of velocity of light in the first medium to that in the second medium is called refractive index of 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 refracting liquid is defined as the ratio of real depth to the apparent depth.

µ = Real depth / Apparent depth

If reading of real depth of the coin = r1

With water = r2

Paper piece = r3

Real depth = r3 – r1

Apparent depth = r3 – r2

µ = r3 – r1 / r3 – r2

Refer to the diagram

PROCEDURE:

1. For accurate measurements of length, depths compound microscope used is provided with a vernier scale which slides along with a main scale.
2. Note the number of divisions of vernier which coincides with number of full scale division.
3. Find the value of each main division and hence least count of microscope
4. Move the microscope very gently. Using the screw focus the eye piece on the coin placed at the bottom of empty container and bring the coin in focus. Note the reading of the microscope as r1.
5. Pour water into the beaker and coin appears to be raised.
6. Move the microscope gradually and again bring the coin in focus. Record reading as r2.
7. Put a piece of paper in water and move the microscope upward till the paper comes into focus. Record the reading as r3.
8. Difference of r3 and r1 gives real depth and r3 and r2 gives app depth.
9. Record your observations and calculate value of µ.

OBSERVATIONS

Least count of traveling microscope:

10 vernier scale division = 9 main scale division

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

CALCULATIONS

RESULTS

The refractive index of water by using traveling microscope is determined to be 1.33.

PRECAUTIONS

1. Least count of the scale of traveling microscope should be calculated.
2. Microscope once focused on the coin, the focusing should not be disturbed throughout the experiment. Only rack and pinion screw should be turned to move the microscope upward.
3. Eye piece should be adjusted that cross wires are distinctly seen.
4. Paper piece should be prevented from getting wet.

ELEMENTS

NITROGEN:

Major fertilizers containing N:

1. Ammonium nitrate (NH4NO3)
2. Potassium nitrate (KNO3)
3. Urea (NH2CONH2)
4. Ammonium sulphate [(NH4)2SO4]

Preparation:

Most of nitrogen fertilizers are obtained form synthetic NH3. This chemical compound is used as gas or in water solution or it is converted to salts.

Nitrogen Deficiencies

1. Pale, green, yellow leaves
2. Stunted growth

Nitrogen in Excess –

1. Lower disease resistance
2. Weaken stem
3. Decay maturity
4. Lower fruit quality

PHOSPHORUS:

Major fertilizers containing P:

1. DAP – Diammonium phosphate [(NH4)2PO4]
2. Ca3(PO4)2 – Calcium phosphate
3. Triple phosphate and super phosphate

Preparation:

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

Phosphorus deficiencies –

1. Pale purple colour on the underside of leaves
2. Reduced flower, fruits and seed production

1. Encourage cell division
2. Hastens maturity, offsetting quick growth caused by N
3. Encourage root growth
4. Increase disease resistance

Phosphorous in excess

1. Causes dehydration of roots
2. Increase soluble salt content of medium

POTASSIUM:

Major fertilizers containining K:

1. Potassium chloride (Potash)
2. Potassium nitrate (KNO3)

Preparation:

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

Potassium deficiencies:

1. Leaves appear dry and scorched
2. Irregular yellow areas on the surface

1. Increase disease resistance
2. Encourage healthy root and stems
3. Essential for starch formation
4. Efficient use of CO2

Potassium in excess

1. Affects soil acidity
2. Reduced flower, fruit and seed production

Fertilisers- V

## Ca2+ confirmed.

RESULT- Fertilizer has Ca2+ as cation. (The fertilizer detected is Vermi Compost).

Fertilizer–III

## Nitrogen present in elemental form.

RESULT- The given fertilizer has N in elemental form. (The fertilizer detected is urea).

(Urea) O.C.N + Na                   NaCN

FERTILIZER 5(vermi compost)

Ca2+ (aq) + CO32-(aq)                  CaCO3 (s) + 2CH3COOH

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

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

Reading of microscope focused on

## 20

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