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3 years ago

What is the boiling point of a solution formed by dissolving 0.75 mol of KCl in 1.00 kg of water?

1 answer:

4 0

The boiling point of water generally increases as the amount of impurities (which a solute like KCl technically can be thought of) dissolved increases. This relation can be quantified using the equation,

$\Delta T_b = i \times K_b \times m$

where $\Delta{T}_{b}$ is the change in the water's boiling point (normally taken to be 100 °C), $i$ is the Van 't Hoff factor (the number of particles a single formula unit of the solute dissociates into in water), $K_b$ is the boiling point elevation constant, and $m$ is the molality (moles of solute/kilogram(s) of solvent) of the solution.

We are forming a solution by dissolving KCl in water. KCl is an electrolyte that, in water, will dissociate into K⁺ and Cl⁻ ions. So, for every formula unit, KCl, we obtain two particles. Thus, the Van 't Hoff factor, or $i$ , will be 2.

The molality of the solution can be calculated by dividing the number of moles of KCl by the mass of water in kilograms. Since we have 1.00 kg of water, we would be dividing 0.75 mol KCl by 1, giving us a molality (m) of 0.75 m.

We aren't provided the boiling point elevation constant for water. Several authoritative sources give the value 0.512 °C/m, so we will adopt that as our $K_b$ .

Note: m = mol/kg as used in this problem.

Plugging everything in,

$\Delta T_b = i \times K_b \times m \\\Delta T_b = 2 \times 0.512 \text{ } \frac{^oC}{mol/kg} \times 0.75 \text{ } \frac{mol}{kg} \\\Delta T_b = 0.768 \text{ } \mathrm{ ^oC}$

As you can see, our change in boiling point is positive (the boiling point is elevated), and it is also quite modest. Taking 100 °C to be the boiling point of pure water, the boiling point of our solution would be 100 ⁰C + 0.768 ⁰C, or 100.768 ⁰C.

If we are considering significant figures, then we must give our answer to two significant figures (since 0.75 has two sig figs). We can regard the boiling point of water (100 ⁰C) as a defined value. Since our final answer is a sum, the boiling point of our solution to two significant figures would be 100.77 ⁰C.

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Solve this word problem:

valina [46]

Answer:

The new acceleration becomes twice the pervious acceleration.

Explanation:

Given that,

Mass of the rock, m = 3 kg

Force, F = 1 N

We know that the force acting on an object is given by :

F = ma

a is acceleration of the rock

Put m = 3 kg and F = 1N,

$a=\dfrac{F}{m}\\\\a=\dfrac{1}{3}\ m/s^2$

If the force is doubled, F' = 2 N

So,

F'=ma'

$a'=\dfrac{F'}{m}\\\\a'=\dfrac{2\times 1}{3}\\\\a'=\dfrac{2}{3}\\\\a'=2\times \dfrac{1}{3}\\\\a'=2a$

So, the new acceleration becomes twice the initial acceleration.

3 0

3 years ago

When I2 and FeCl2 are mixed together, iodine (I) cannot replace chlorine (Cl) in the compound because iodine is lower on the per

Nata [24]

Answer: The given statement is true.

Explanation: If this reaction would have occurred, then this reaction would be considered as displacement reaction.

Displacement reactions are the reaction in which more reactive element displaces the less reactive element in a chemical reaction. This is based on the reactivity of elements.

Reactivity of elements is the tendency of the elements to gain or loose electrons. The reactivity decreases down the group in a periodic table.

In the given reaction, Iodine and chlorine are the elements of the same group in the periodic table and iodine lies below chlorine in the group. So, the reactivity of iodine is less than the reactivity of chlorine.

Hence, in the given reaction, iodine will not replace chlorine because it lies below in the periodic table.

$FeCl_2+I_2\rightarrow \text{No reaction}$

3 0

4 years ago

A standard solution of FeSCN2+ is prepared by combining 9.0 mL of 0.20 M Fe(NO3)3 with 1.0 mL of 0.0020 M KSCN . The standard so

Xelga [282]

Answer : The equilibrium concentration of $SCN^-$ in the trial solution is $4.58\times 10^{-8}M$

Explanation :

First we have to calculate the initial moles of $Fe^{3+}$ and $SCN^-$ .

$\text{Moles of }Fe^{3+}=\text{Concentration of }Fe^{3+}\times \text{Volume of solution}$

$\text{Moles of }Fe^{3+}=0.20M\times 9.0mL=1.8mmol$

and,

$\text{Moles of }SCN^-=\text{Concentration of }SCN^-\times \text{Volume of solution}$

$\text{Moles of }SCN^-=0.0020M\times 1.0mL=0.0020mmol$

The given balanced chemical reaction is,

$Fe^{3+}(aq)+SCN^-(aq)\rightleftharpoons FeSCN^{2+}(aq)$

Since 1 mole of $Fe^{3+}$ reacts with 1 mole of $SCN^-$ to give 1 mole of $FeSCN^{2+}$

The limiting reagent is, $SCN^-$

So, the number of moles of $FeSCN^{2+}$ = 0.0020 mmole

Now we have to calculate the concentration of $FeSCN^{2+}$ .

$\text{Concentration of }FeSCN^{2+}=\frac{0.0020mmol}{9.0mL+1.0mL}=0.00020M$

Using Beer-Lambert's law :

$A=\epsilon \times C\times l$

where,

A = absorbance of solution

C = concentration of solution

l = path length

$\epsilon$ = molar absorptivity coefficient

$\epsilon$ and l are same for stock solution and dilute solution. So,

$\epsilon l=\frac{A}{C}=\frac{0.480}{0.00020M}=2400M^{-1}$

For trial solution:

The equilibrium concentration of $SCN^-$ is,

$[SCN^-]_{eqm}=[SCN^-]_{initial}-[FeSCN^{2+}]$

$[SCN^-]_{initial}$ = 0.00050 M

Now calculate the $[FeSCN^{2+}]$ .

$C=\frac{A}{\epsilon l}=\frac{0.220}{2400M^{-1}}=9.17\times 10^{-5}M$

Now calculate the concentration of $SCN^-$ .

$[SCN^-]_{eqm}=[SCN^-]_{initial}-[FeSCN^{2+}]$

$[SCN^-]_{eqm}=(0.00050M)-(9.17\times 10^{-5}M)$

$[SCN^-]_{eqm}=4.58\times 10^{-8}M$

Therefore, the equilibrium concentration of $SCN^-$ in the trial solution is $4.58\times 10^{-8}M$

5 0

4 years ago

If two elements are in the same column what do they have in common

nikdorinn [45]

They have the same number of electrons in their outer shells. Elements in the same group often share similar chemical properties because the outer electrons generally determine a lot of their properties

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4 years ago

An ice cube floats in warm water in a container placed outside on a hot, sunny day.

SCORPION-xisa [38]

Answer:

Firsthand association assigns energy throughout conduction. Radiation transpires when particles consume energy that progresses as a wave. The heat will run from the h2O to the ice continuously until the ice has absolutely melted so both elements have reached the same temperature.

Explanation:

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3 years ago