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Experiment NO.1

Density and relative density

Name: Yasir Ammar Ahmed

Department of Petroleum

Engineering

Class – 2 –

2nd Year

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Contents : Introduction --------------- Page 3

The Objectives --------------Page 4

Materials and Instruments --------------Page 4

Procedure ----------------Page 6

Calculations and Results -------------Page 8

Discussion ------------ Page 11

Theory ------------------ Page 13

Conclusion -------------Page 13

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Introduction

The purpose of this experiment is to understand the meaning

and significance of the density of a substance. Density is a basic

physical property of a homogeneous substance; it is an

intensive property, which means it depends only on the

substance's composition and does not vary with size or

amount. The determination of density is a nondestructive

physical process for distinguishing one substance from another.

Density is the ratio of a substance's mass to its own volume.

𝜌 = 𝑚𝑎𝑠𝑠

𝑣𝑜𝑙𝑢𝑚𝑒=

𝑣

𝑚

In the metric system the unit of density for a liquid or solid is

measured in g/mL or g/cm3.l

By determining the density of matter and in our case we will

take the density of (kerosin and Gas oil ) we can calculate the

API (American Petroleum Institute) by the equation :

API K = 141.5

𝑅𝐷− 131.5

Where (RD) is the relative density of the matter and we can

find it by dividing the density of matter to the density of water ,

API gravity, is a measure of how heavy or light

a petroleum liquid is compared to water: if its API gravity is

greater than 10, it is lighter and floats on water; if less than 10,

it is heavier and sinks.

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The Objectives :

The objectives of this experiment is :

1. To learn how to determine the density of sample.

2. To learn how to determine the relative density of sample.

3. To learn how to use the hydrometer and pycnometer and

how to take dimensions of them.

4. To learn how to calculate the API gravity by relative

density.

5. To distinguish between the different density samples.

Materials and Instrument

The Materials that we have used in the experiment are :

1. Graduated cylinder(500mL): is a piece of laboratory

equipment used to measure the volume of a liquid,the

inside diameter of the cylinder shall be at least 25mm

greater than the outside diameter of the hydrometer and

the height shall be such that the appropriate hydrometer

floats in the test portion with at least 25mm clearance

between the bottom if the hydrometer and the bottom of

the cylinder.(fig1)

2. Pycnometer(50mL) : A pcynometer or specific gravity

bottle is a flask with a stopper that has a capillary tube

through it, which allows air bubbles to escape. The

pycnometer is used to obtain accurate measurements of

density.(fig2)

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3. Hydrometer ( 0.7 – 0.8) and (0.8 – 0.9) : is an instrument

used to measure the specific gravity (or relative density)

of liquids; that is, the ratio of the density of the liquid to

the density of water.(fig3)

4. Two samples of (Kerosin) and (Gas Oil)

5. Scientific Balance : Used for determining the weight or

mass of a sample.(fig4)

Fig1 Fig2

Fig3 Fig4

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Procedure:

In our experiment we have not adjust the temperature of the

sample (Just for this time because it was the first lab &Exp.)

Method 1 : Hydrometer

1. First take a clean and dry graduated cylinder 500mL ,the

inside diameter of the cylinder shall be at least 25mm

greater than the outside diameter of the hydrometer and

the height shall be such that the appropriate hydrometer

floats in the test portion with at least 25mm clearance

between the bottom if the hydrometer and the bottom of

the cylinder.

2. Fill the graduated cylinder with the test portion (in our

case they were Kerosin & Gas oil ), we fill it with only one

test portion till it reach the 500mL dimension.

3. Now lower the appropriate hydrometer into the liquid

and release when in a position of equilibrium.

4. Allow sufficient time for the hydrometer to come to rest.

5. When the hydrometer is flow freely take the scale reading

where the principle surface of the liquid cuts the scale by

placing the eye slightly below the level of liquid and

slowly go up till you read the scale at the liquid sureface.

6. When you record the reading immediately lift the

hydrometer and clean it.

7. Now we got the relative density (specific gravity ) value ,

by applying it at the API gravity formula we get the API

gravity value , and that's our goal of this experiment.

API = 141.5

𝑅𝐷− 131.5

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Method 2 : Pycnometer

1. First take a clean and dry Pycnometer 50mL and weigh

it by using scientific balance.

2. Record the weight of empty , dry and clean

pycnometer and after recording the weight lift it.

3. Fill the pycnometer fully with the test portion (the

sample) , and after that weigh it again by using the

balance.

4. Record the weight of fully filled pycnometer with test

portion(the sample).

5. By the records of weights of empty and fully saturated

pycnometer we can calculate the weight of the test

portion(the sample) , and by dividing it on the volume

of the pycnometer we will get the Density of the test

portion(the sample).

6. Now take the room temperature and record it.

7. By the room temperature we can determine the

density of water from the table below(Table 1).

8. Now we have the density of the sample and the

density of water , by applying the relative density (

specific gravity ) formula we can get the relative

density ( specific gravity) value.

9. Now we have the relative density (specific gravity )

value , by applying it at the API gravity formula we get

the API gravity value of the sample , and that's our goal

of this experiment.

API gravity = 141.5

𝑅𝐷− 131.5

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Calculation and Result

Method 1 : Hydrometer

Givens :

RD = SGk = 0.786

RD = SGD = 0.827

Required: API of Kerosin(K)

API of Gas Oil(D) Solution :

API K = 141.5

𝑅𝐷− 131.5

= 141.5

0.786− 131.5 = 180.03 − 131.5

= 48.53

API D = 141.5

𝑅𝐷− 131.5

= 141.5

0.827− 131.5 = 171.10 – 131.5

=39.60

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Method 2 : Pycnometer

Givens : For kersoen

Volume of Pycnometer = 50 mL

M0 = 19.2 g M1 = 61.5 g T = 21.5oC

Requireds :

SG K = ? API K = ?

Solution :

SG K = 𝜌𝑘

𝜌𝑤

𝜌𝑘

= 𝑀𝑘

𝑉 → Mk = M1 - M2 = 61.5 g – 19.2 g = 42.3 g

𝜌𝑘

= 42.3 𝑔

50 𝑚𝐿 = 0.846 g/mL

While T = 21.5oC So 𝜌𝑤 = 0.9978845 g/mL

SG K = 0.846 𝑔/𝑚𝐿

0.9978845 g/mL= 0.847

API K = 141.5

0.847− 131.5 = 167.06 − 131.5 = 35.56

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Givens : For Gas Oil

Volume of Pycnometer = 50 mL

M0 = 18 g M1 = 60 g T = 21.5oC

Required :

SG D = ? API D= ?

Solution :

SG D = 𝜌𝐷

𝜌𝑤

𝜌𝐷

= 𝑀𝐷

𝑉 → MD = M1 - M2 = 60 g – 18 g = 42 g

𝜌𝐷

= 42 𝑔

50 𝑚𝐿 = 0.840 g/mL

While T = 21.5oC So 𝜌𝑤 = 0.9978845 g/mL

SG D = 0.840 𝑔/𝑚𝐿

0.9978845 g/mL= 0.842

API D = 141.5

0.842− 131.5 = 168.05 − 131.5 = 36.55

Note : How I Got the Temperature at 21.5 while it is not included at the Table

I did this calculation

The 𝜌𝑤 at 21oC = 0.997991 and 𝜌𝑤 at 22oC = 0.997769

𝜌𝑤=(0.997991 + 0.997769) / 2 = 0.9978845

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Discussion

In this experiment , there are a lot of questions we should know

there answers , first of all is our results that we got

After calculations and got the results of the both methods

(Hydrometer & Pycnometer) we can see the different in API

results that we got it , in the first method we got API gravity of

Kerosin equal (48.53) while in the second method equal(35.56

) as you see there is a high range between the two methods ,

and here the question is , which method is much accurate ?

My answer is , the method 2 is more accurate than the method

1 , the reason belongs to that the hydrometer method is

affected by many factors that can make the reading not

accurate , the factors are :

1. Temperature : Temperature has an effect on the

hydrometer reading , because when the temperature is

increase the density of the sample will decrease and then

the reading of hydrometer will be not accurate, and cause

the hydrometer float slightly low , so when we use the

hydrometer it should be at fixed temperature , at 60oF .

2. carbon dioxide bubbles : produced by yeast rise and

dissipate into the air above. Early in fermentation when

the must is visibly bubbling, the bubbles will attach

themselves to the hydrometer and cause it to float

higher, increasing the reading slightly.

3. Presence of Alcohol : Alcohol is less dense than water and

thus makes a hydrometer float a little lower.

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4. Other errors should taking the read from non-parallel site

to the eye , that could make the calculations and results

not accurate.

So after all that factors affecting on the result of hydrometer

, we see that the results are not accurate with method 1 .

Method 2 is more accurate than method 1 , and the wrong

or error percentage is less than method 1 , in method 2 we

take the mass of the liquid , which is constant and also the

volume of pycnometer is constant , if we do the experiment

at fixed temperature we will get accurate results about

density therefore accurate results about API gravity .

The more API gravity value of crude oil is more expensive

and more effectual because its contain more gasoline and it

is the most wanted product at the whole world , because all

people are looking for gasoline to operate their machines ,

so the more API gravity value contain more gasoline and

that's what we looking for .

only about less percentage of crude oil can be transfer to

gasoline , only 5-6 % of Tawke crude oil at (Kashi mini

Refinery ) can be transferred to gasoline.

The other advantage of API gravity value that we can

determine the sulfur contain in crude oil , the higher value if

API gravity means the less contain of sulfur , the high levels

of sulfur contains can be toxic and dangerous and can cause

breathing hazards .

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Theory

When greater accuracy is required or when only small

quantities are available, liquid densities are best obtained from

the mass required to fill a vessel of accurately defined volume,

e.g., a specific gravity bottle(p.217) or a pycnometer. With

careful technique, the densities measured with pycnometers

are precise to five significant figures. For not too viscous liquids

available in sufficient amounts, density is more conveniently

determined by buoyancy devices namely Westphal balance or a

Hydrometer. These devices are based on Archimedes principle

according to which the buoyant effect(the upthrust acting on

an object immersed in a liquid) is directly proportional to the

weight of the liquid displaced.

Conclusion

In this Experiment we learn how to measure the density of

sample and how to calculate the API gravity by density , and

the other thing is how to use the hydrometer and

pyconmeter to determine the density of samples , and we

learn what does the API gravity different values mean , and

the error s sources that can make the measurements not

accurate.