[5 Mark Question Answer]

Question 15 Marks

Explain the procedure to determine the density of an unknown liquid using a relative density bottle.

Answer

The density of an unknown liquid can be determined using a relative density bottle as follows.
Step $1$ : Wash the $\text{RD}$ bottle with distilled water. Dry it well.
Step $2$ : Insert the stopper and find its mass using the balance. Note down the mass of the empty $\text{RD}$ bottle.
Step $3$ : Fill the bottle with distilled water. Insert the stopper. Some water will drain out through the stopper. Dry the bottle well from outside.
Step $4$ : Find the mass of the bottle filled with distilled water.
Step $5$ : Empty the bottle and dry it well. Fill it with the liquid whose relative density is to be determined and insert the stopper. Some liquid will drain out through the stopper. Dry the bottle well from outside. Find the mass of the bottle filled with liquid.
Step $6$ : Do the calculations as follows.
Mass of the empty bottle $= m1$
Mass of bottle $+$ distilled water $= m2$
Mass of bottle $+$ liquid $= m3$
Mass of distilled water $– (m2 – m1)$
Relative density of the liquid $=\frac{m_3-m_1}{m_2-m_1}$
Mass of liquid $= (m3 – m1)$
As volume of both the liquid and water are the same,
Density of the liquid $=\frac{m_3-m_1}{m_2-m_1} \times 1 g / cm ^3$

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Question 25 Marks

Explain why solids have greater densities than liquids and liquids have greater densities than gases.

Answer

Density in Solids : The density of a substance is affected by the concentration of molecules in a given volume of the substance. In solids, the intermolecular spaces forces are the strongest and the intermolecular spaces very small. This implies that the molecules of solids are very closely packed in a small volume. Hence, solids have high density due to the large number of molecules in a small volume.
Density in Liquids : In liquids, the intermolecular forces are weaker as compared to that in solids and the intermolecular spaces are larger than that in solids. This implies that the molecules of liquid are less tightly packed in a small volume as compared to solids. Hence, liquids have less density than solids.
Density in Gases : In gases, the intermolecular forces are negligible and the intermolecular spaces are much larger than that in liquids. This implies that tfieTnMecules of gases are very less tightly packed in a small volume as compared to liquids. Hence, gases have less density than liquids and solids.

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Question 35 Marks

How can you determine the density of an irregular solid with the help of a measuring cylinder?

Answer

To measure the density of an irregular solid, both its mass and volume have to be measured. Its mass $(m)$ can be determined with the help of a physical balance. Its volume can be measured with the help of a measuring cylinder as follows.
Step $1 :$ Pour some water in the measuring cylinder and record the level of water in the cylinder from the graduations marked on its walls.
Step $2 :$ Tie the string around the stone and lower it into the cylinder gently without touching its walls or the bottom, until it is completely immersed.
Step $3 :$ The level of water in the cylinder rises. Note down the level of water in the cylinder again.
Step $4 :$ If initial level of water is $V_1$ and final level of water is $V_2,$ then the volume of the solid is calculated to be $V_2-V_1$The density of the solid can be determined from the formula,
Density $=$ Undefined control sequence $\over$

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Question 45 Marks

An empty $RD$ bottle weighs $60\ g$ but weighs $120\ g$ when completely filled with water. When the bottle is completely filled with an unknown liquid, it weighs $90 \ g$. Calculate the
$a$. volume of the $RD$ bottle.
$b$. density of the unknown liquid.

Answer

Mass of empty $RD$ bottle $, m1 = 60\ g$
Mass of bottle $+$ water $, m2 = 120\ g$
Mass of bottle $+$ unknown liquid $, m3= 90\ g$
Mass of water $= m2 – m1 = 120\ g – 60\ g = 60 \ g$
Mass of unknown liquid $= m3 – m1 = 90\ g – 60\ g = 30\ g$
$a$. As density of water is $1\ g / \ cm ^3,$
therefore,
volume of water $=\frac{\text { mass of water }}{\text { density of water }}$
$=\frac{60 g}{1 g / \ cm ^3}=60 \ cm^3$
$b$. Volume of an unknown liquid $=$ volume of water $=60 \ cm^3$
Density of an unknown liquid
$=\frac{\text { mass of an unknown liquid }}{\text { volume of an unknown liquid }}=0.5 \ g / \ cm ^3$

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PHYSICS [5 Mark Question Answer]

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