Tag: various mixtures

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Multiple choice chemistry mix and separate different types of solutions various mixtures introduction to solutions

If the heat of combustion of carbon monoxide at constant volume and at $17^o$C is $-283.3$ kJ, then its enthalpy of combustion at constant pressure($R=8.314J degree^{-1} mol^{-}$)

  1. $-284.5$ kJ
  2. $284.5$ kJ
  3. $384.5$ kJ
  4. $-384.5$ kJ
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Solution:- (A) $- 284.5 \; kJ$
Heat change at constant volume for the combustion of carbon monoxide $= -283.3 \; kJ$
${CO} _{\left( g \right)} + \cfrac{1}{2} {{O} _{2}} _{\left( g \right)} \longrightarrow {C{O} _{2}} _{\left( g \right)}$
From the above reaction,
$\Delta{{n} _{g}} = {n} _{P} - {n} _{R} = 1 - \left( \cfrac{1}{2} + 1 \right) = - \cfrac{1}{2}$
Temperature $\left( T \right) = 17 ℃ = \left( 17 + 273 \right) K = 290 K \; \left( \text{Given} \right)$
Now from first law of thermodynamics,
$\Delta{H} = \Delta{E} + \Delta{{n} _{g}} RT$
$\Delta{H} = -283.3 + \left( -\cfrac{1}{2} \right) \times 8.314 \times {10}^{-3} \times 290$
$\Rightarrow \Delta{H} = -283.3 - 1.205 = - 284.505 \; kJ$
Hence the heat of reaction at constant pressure will be $- 284.5 \; kJ$.
Multiple choice chemistry mix and separate different types of solutions various mixtures introduction to solutions

Dissolution of ionic solid in water is possible when:

  1. $H$ lattice $> H$ hydration
  2. $H$ lattice $= H$ hydration
  3. $H$ hydration $: H$ lattice = 2:1
  4. $H$ hydration $> H$ lattice
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Solution:- (D) ${H} _{\text{hydration}} > {H} _{\text{lattice}}$

In order to dissolve an ionic solid, water molecules must break up the interactions between all of the ions in the solid. The heat of hydration $\left( {H} _{\text{hydration}} \right)$ offsets the lattice energy $\left( {H} _{\text{lattice}} \right)$ of an ionic solid to allow for solution formation to occur typically when ${H} _{\text{hydration}} > {H} _{\text{lattice}}$.

Multiple choice chemistry mix and separate different types of solutions various mixtures introduction to solutions

For an ideal binary liquid solution with $P^{\circ} _{A} > P^{\circ} _{B}$, which relation between $X _{A}$ (mole fraction of A in liquid phase) and $Y _{A}$(mole fraction of $A$ in vapour phase) is correct?

  1. $Y _{A} < Y _{B}$
  2. $X _{A} > X _{B}$
  3. $\dfrac{Y _{A}}{Y _{B}} > \dfrac{X _{A}}{X _{B}}$
  4. $\dfrac{Y _{A}}{Y _{B}} < \dfrac{X _{A}}{X _{B}}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For an ideal binary liquid solution with $P _\overset {o}{A}>P _\overset {o}{B}$.

We know that, from Henry's law
$P _\overset {o}{A}\propto X _A$
So, $X _A > X _B$.
If mole fraction of $A$ in liquid phase is more then mole fraction of $A$ in vapour phase is less so, $Y _A < Y _B$.

Multiple choice chemistry mix and separate different types of solutions various mixtures introduction to solutions

Which of the following are correct about Tyndall effect?

  1. True solution do not show Tyndall effect due to very small size of the particles

  2. The diameter of the particles of the dispersed phase must not be much smaller than the wavelength of light used

  3. Tyndall effect is very weak in case of lyophobic sols

  4. The refractive index of the dispersed phase and dispersion must differ considerably
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The Tyndall effect is the scattering of light by colloidal particles. True solutions have particle sizes < 1 nm, which are too small to scatter visible light (wavelength ~400-700 nm). For the effect to be observable, the dispersed phase particles must have dimensions comparable to the wavelength of light - not much smaller. Option B states they must NOT be much smaller, which would mean they ARE comparable, which is correct for observing the effect. However, B contradicts standard textbook wording. Option A correctly states true solutions don't show Tyndall effect due to very small particle size.

Multiple choice chemistry mix and separate different types of solutions various mixtures introduction to solutions

$100\ ml$ of an aqueous solution contains $6.0\times {10}^{21}$ solute molecules. The solution is diluted to $1$ lit. The number of solute molecules present in $10\ ml$ of the dilute solution is:

  1. $6.0\times {10}^{20}$
  2. $6.0\times {10}^{19}$
  3. $6.0\times {10}^{18}$
  4. $6.0\times {10}^{17}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
100 ml solution diluted to 1 liters (1000) ml contains $6.0 \times 10^{21}$ solute molecular

No of molecules present in 10 ml

$ = \dfrac{10 \times 6.0 \times 10 ^{21}}{1000} = 6 \times 10 ^{19} $

Multiple choice chemistry mix and separate different types of solutions various mixtures introduction to solutions

Highly pure dilute solution of sodium in liquid ammonia:

  1. on evaporation yield metals.

  2. exhibits electrical conductivity.

  3. produces sodium amide and hydrogen gas instantly.

  4. acts as powerful reducing agent.
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
Explanation

$M+(x+y)NH _3\rightarrow [M(MH _3) _x]^++[4(NH _3) _y]^-$. Blue colour of the solution is due to ammoniated electrons and good conductor of electricity because of both ammoniated cations and ammoniated electrons.

Multiple choice chemistry mix and separate different types of solutions various mixtures introduction to solutions

The compound whose 0.1 ml solution isbasic is :

  1. Ammonium acetate

  2. Ammonium chloride

  3. Ammonium sulphate

  4. Sodium acetate
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Sodium acetate is a salt of a strong base (NaOH) and a weak acid (CH3COOH). When dissolved in water, it undergoes hydrolysis to produce a basic solution with a pH greater than 7. The other salts listed are formed from strong acids and weak bases, resulting in acidic solutions.

Multiple choice chemistry mix and separate different types of solutions various mixtures introduction to solutions
The phenol-water system has a upper critical solution temperature.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The given statement is true.
The phenol-water system has a upper critical solution temperature.
Above this temperature, the components of phenol-water system are miscible in all proportions.
The upper critical solution temperature is an upper limit to a temperature range of partial miscibility, or miscibility for certain compositions only.

Multiple choice chemistry mix and separate different types of solutions various mixtures introduction to solutions

When some liquid evaporates, the average speed of the molecules remaining will .......... .

  1. Increase because the more energetic molecules have left

  2. Decrease because the more energetic molecules have left

  3. Remain unchanged because all molecules have about the same speed

  4. Increase because there are fewer molecules
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Answer is B.

A liquid is comprised of molecules that are in constant motion, traveling at different rates. The average speed of these particles depends on the liquids temperature.  A rise in temperature increases molecular velocity as well as aggregate kinetic energy.  If molecules gain enough energy, their fast-moving particles will begin to bump against their neighbors.  Eventually, particles near the liquids surface will impart sufficient speed, and therefore sufficient kinetic energy, to cause the surface particles to propel away from the liquid in the form of gaseous molecules or, more simply, as water vapor.
As the particles with the highest kinetic energy levels evaporate, the average kinetic energy of the remaining liquid (sweat) decreases.  Because a liquids temperature is directly related to the average kinetic energy of its molecules, the liquid cools as it evaporates.
Hence, when some liquid evaporates, the average speed of the molecules remaining will decrease because the more energetic molecules have left.