Tag: liquid crystals

Questions Related to liquid crystals

Most elements are solids at 25$^o$C and 1 atm pressure, the exception being the 11 elements that are gases and 2 that are liquids. What 2 elements are liquids?

chemistry materials liquid crystals liquid state the liquid state

  1. Hg and Br

  2. Hg and I

  3. Ag and Kr

  4. Au and Kr

  5. Pt and Co

Show answer
Correct Option: A
Explanation:

At room temperature, that is $25^o C$ and $1$atm, Mercury and Bromine both exist as liquids. Hence option A gives the correct pair.

Iodine, Silver, Platinum, Cobalt are all solid at room temperature. Whereas, Krypton is a gas at room temperature.                                            

With increase in temperature, viscosity and surface tension of a liquid respectively:

chemistry materials liquid crystals liquid state the liquid state

  1. Decrease, decrease

  2. Increase, increase

  3. Increase, decrease

  4. Decrease, increase

Show answer
Correct Option: A
Explanation:
Temperature is increased.
1) As the temperature of a liquid increases,the movement of its molecule increases,which disturbs the imbalanced forces on the surface of liquid.thus the barrier of tightly bound molecules weakens thereby,Surface tension decreases.
2) As the temperature of a liquid increases,the energy of its molecules increases which increases the movement of molecules.so the liquid becomes more fluid.thus viscosity of liquid decreases.

Which of the following increases with the increase in temperature in case of liquid?

chemistry materials liquid crystals liquid state the liquid state

  1. Surface tension

  2. Vapour pressure

  3. Viscosity

  4. Boiling point

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Correct Option: B
Explanation:
Vapour pressure increases with increase in temperature. Because, in a closed container solution contains, higher the temperature high will be the evaporation then the pressure created due to vapor i.e vapor pressure increases.
Ans :- Option B.

Which is a more volatile liquid?

chemistry materials liquid crystals liquid state the liquid state

  1. $C _{2}H _{5}OH$

  2. $CH _{3}COOH$

  3. $C _{2}H _{5}OC _{2}H _{5}$

  4. $C _{6}H _{6}$

Show answer
Correct Option: D
Explanation:

Presence of hydrogen bonding in a liquid decreases its volatile nature. This is because due to hydrogen bonding, there is more association between the molecules and the tendency to go into gaseous phase decreases. Hence, $C _6H _6$ will be more volatile liquid since it has no hydrogen bonding.

$510 mg$ of a liquid on vaporization in victor Mayer's apparatus displaces $67.2 ml$ of dry air (at NTP). The molecular weight of liquid is:

chemistry materials liquid crystals liquid state the liquid state

  1. $130$

  2. $17$

  3. $1700$

  4. $170$

Show answer
Correct Option: B
Explanation:

As we know that $1g$ mole of any gas occupies as $22400ml$ of volume at STP

So molecular mass of compound= $\cfrac {0.510\times 22400}{67.2}$
$\Rightarrow 16.999 \approx 17$

When a student was given aviscometer, the liquid was sucked with difficulty, the liquid may be:

chemistry materials liquid crystals liquid state the liquid state

  1. benzene

  2. toluene

  3. water

  4. glycerine

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Correct Option: D
Explanation:

Among the given liquid glycerine is a viscous liquid and hence it was sucked with difficulty.

How many of the following properties are shown by liquid  state?
Rigidity, Definite volume. No free surface, Define shape

chemistry materials liquid crystals liquid state the liquid state

  1. $1$

  2. $2$

  3. $3$

  4. $4$

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Correct Option: A
Explanation:

The properties of liquids are as follows:

  • It does not have a fixed shape but it has a fixed volume.
  • It does not have definite shape.
  • It has a free surface.
  • It does not show rigidity.

The temperature remains constant during melting and all the ice changes into water. The enthalpy change associated with this process is due to _____________.

chemistry materials liquid crystals liquid state the liquid state

  1. latent heat of fusion

  2. latent heat of vaporisation

  3. latent heat of evaporation

  4. latent heat of sublimation

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Correct Option: A
Explanation:

Latent heat is the energy released or absorbed by a body during a constant temperature process. An example is a phase transition such as ice melting or water boiling. Heat absorbed during melting is called latent heat fusion.

Can water be made to boil in a paper cup without the paper being burnt. This is because ___________.

chemistry materials liquid crystals liquid state the liquid state

  1. temperature of water does not change during boiling.

  2. ignition temperature of paper is higher than the boiling point of water

  3. high latent heat of vaporization of water

  4. All the above

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Correct Option: D
Explanation:

The paper cup in which water is placed is having ignition temperature higher than the  boiling point of water, and water have high latent heat of vaporization. This is also possible that temperature provided to water does not exceed its boiling point. Hence, water can boil in paper cup without burning the cup.

Why does temperature remain constant as a liquid is heated and gets converted to its gaseous state at its boiling point? 

chemistry materials liquid crystals liquid state the liquid state

  1. Due to increase in potential energy

  2. Due to increase in kinetic energy 

  3. Due to decrease in potential energy

  4. Due to decrease in kinetic energy

Show answer
Correct Option: B
Explanation:

As a liquid is heated at constant pressure, its temperature increases. This trend continues until the boiling point of the liquid is reached. No further rise in temperature of the liquid can be induced by heating due to increase in kinetic energy.