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Relative density
(JAMB (UTME))
Presented by
BAMGBADE, A A
Btech. Biochemistry(LAUTECH),
Msc. Biochem(UNILORIN)
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Learning outcomes
At the end of this presentation, listeners should be able
to :
▪ define relative density(R.D).
▪ state the formulas for calculating relative density of a
substance.
▪ state another name for relative density.
▪ solve relevant UTME questions relating to Relative
density.
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◊ Relative Density(RD) / Specific gravity
◊Relative density, RD of a substance is the ratio of the
density of the substance to the density of the water.
◊ if d= density of substance and
Then, R.D=
= =
=
�
�
�
= density of water
�
◊ The relative density of water is 1.0
◊ All metals and most solids have R.D greater than 1
while air and several liquids have R.D less than 1.
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◊ Sample Questions from UTME
□Q1:1980, no 30: The relative density of zinc,
brass, copper, gold and silver are respectively
7.1,8.5,8.9,19.3,10.5. A metal ornament which
weighs 0.425kg and can displace 50 x − � of
water is made of
A. Zinc B. brass C. copper D. gold E. silver.
→Solution: m= 0.425kg, v= 50 x − �
.
−
→ Recall : D= →
=
8.5
x
���
50 x −6 3
But R.D=
�
�
=
8.5 x
3
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−3
= 8.5(B)
◊ Sample Questions from UTME
□ Q2: 1991, no12: The mass of a stone is 15.0g
when completely immersed in water and 10.0g when
completely immersed in a liquid of relative density
2.0. The mass of the stone in air is
A. 5.0g B. 12.0g C. 20.0g D. 25.0g
→ Solution:mass in water= 15g,
mass in liquid= 10g
Mass in air(a)?
−
→ 2=
Recall: R.D=
→ 2(m-15)= m-10
→ 2m-m= 30-10
→ 2m-30= m-10
→ m= 20.0g(C)
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−
◊ Sample Questions from UTME
□Q3: 1994, no18:The mass of a specific gravity bottle
is 15.2g when it is empty. It is 24.8g when filled with
kerosene and 27.2g when filled with distilled water.
Calculate the relative density of the kerosene.
A. 1.25 B. 1.10 C. 0.90 D. 0.80
→Solution: mass of empty bottle, � = 15.2,
mass when filled with kerosene, � + = 24.8g
mass when filled with water, � + = 27.2g
mass of kerosene= � -� = 24.8-15.2=9.6
similarly, mass of water= � - � = 27.2-15.2=12
9.
→ Recall, R.D=
=
= 0.8(D)
�
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◊ Sample Questions from UTME
Q4:2008, no16: In the Hare’s apparatus, water rises
to a height of 26.5 � in one limb. If a liquid rises to a
height of 20.4 � in the other limb, what is the
Relative density of the liquid?
A. 0.8 B. 1.1 C. 1.2 D. 1.3
→Solution: ℎ = 20.4 � , ℎ = 26.5 �
Using R.D=
ℎ
ℎ�
=
.
.
= 0.7667(A)
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◊ Practice Questions from UTME
□Q1: 2006, no 14, If the relative density of gold is
19.2, the volume of 2.4kg of gold is
A. 1.9 x − � B. 4.61 x − � C. 8.00 x − �
���− )
D. 1.25 x − � (Density of water=
{Expected Answer: 1.25 x − � (D) }
□Q2: 1997, no 19: An empty 60litre petrol tank has a
mass of 10kg. Its mass when full of fuel of relative
density 0.72 is?
A. 7.2kg B. 33.3kg C. 43.3kg D. 53.3kg
{ Expected Ans: 43.3kg : C}
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Next video will be
Archimede’s principle
with sample
Questions and Solutions from
UTME
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