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Makovka662 [10]

3 years ago

9

Why is flameless heating used for heating a solution in hexane or diethyl ether during a recyrstallization?

1 answer:

kkurt [141]3 years ago

6 0

The technique which is used to purify the chemicals is said to be recrystallization.

In this process, solute is dissolved in a particular solvent and according to its principle, the quantity of solute which is dissolved by solvent increases with increase in temperature. The solutes are more soluble at high temperatures in comparison to room temperature (insoluble) or low temperature. Therefore, heating is needed to dissolve the solute in the solvent.

Now, in the case of hexane or diethyl ether, flameless heating is required because of their low boiling points implies if they heat directly on fire, then they have tendency to catch fire. Thus, hexane and diethyl ether are highly flammable.

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Calculate the enthalpy change (in joules) involved in converting 5.00 grams of water at 14.0 °c to steam at 115 °c under a const

tensa zangetsu [6.8K]

Enthalpy change is the term given to the concentration of the heat absorbed or evolved in a reaction carried out at a constant pressure. It is given by the symbol ΔH.

Enthalpy change = m (Cwater × dT + Hvap + Csteam × dT

dHvap = 40.67 kJ/mol = 40.67 × 103/18 = 2259.4 J/g

Enthalpy change = 5.00 [4.18 × (100-14) + 2259.4 + 1.84 × (115-100)]

= 13232.4 J

7 0

3 years ago

Aspirin (acetylsalicylic acid, C9H8O4) is a weak monoprotic acid. To determine its acid-dissociation constant, a student dissolv

Triss [41]

Answer:

1. $3.57\times 10^{-4}$ was the $K_a$ value calculated by the student.

2. $5.93\times 10^{-4}$ was the $K_b$ of ethylamine value calculated by the student.

Explanation:

1.

The $pH$ value of Aspirin solution = 2.62

$pH=-\log[H^+]$

$[H^+]=10^{-2.62}=0.00240 M$

Moles of s asprin = $\frac{2.00 g}{180 g/mol}=0.01111 mol$

Volume of the solution = 0.600 L

The initial concentration of Aspirin = c = $\frac{0.01111 mol}{0.600 L}=0.0185 M$

$HAs\rightleftharpoons As^-+H^+$

initially

c 0 0

At equilibrium

(c-x) x x

The expression of dissociation constant :

$K_a=\frac{[As^-][H^+]}{[HAs]}$ :

$K_a=\frac{x\times x }{(c-x)}$

$=\frac{0.00240 M\times 0.00240 M}{(0.0185-0.00240 )}$

$K_a=3.57\times 10^{-4}$

$3.57\times 10^{-4}$ was the $K_a$ value calculated by the student.

2.

The $pH$ value of ethylamine = 11.87

$pH+pOH=14$

$pOH=14-11.87=2.13$

$pOH=-\log[OH^-]$

$[OH^-]=10^{-2.13}=0.00741 M$

The initial concentration of ethylamine = c = 0.100 M

$C_2H_5NH_2+H_2O\rightleftharpoons C_2H_5NH_3^{+}+OH^-$

initially

c 0 0

At equilibrium

(c-x) x x

The expression of dissociation constant :

$K_b=\frac{[C_2H_5NH_3^{+}][OH^-]}{[C_2H_5NH_2]}$ :

$K_b=\frac{x\times x}{(c-x)}$

$=\frac{0.00741\times 0.00741}{(0.100-0.00741)}$

$K_b=5.93\times 10^{-4}$

$5.93\times 10^{-4}$ was the $K_b$ of ethylamine value calculated by the student.

3 0

3 years ago

Suppose 0.035 moles of HCl is dissolved in enough water to produce 750 mL of solution. What is the pH

zhuklara [117]

Answer:

pH = 1.33

Explanation:

Because HCl is a strong acid, each mole of HCl will completely dissociate into H⁺ and Cl⁻ species.

Now we calculate the molar concentration (molarity) of H⁺:

Molarity = moles / volume

(750 mL ⇒ 750 / 1000 = 0.750 L)

Molarity = 0.035 moles / 0.750 L

Molarity = 0.0467 M

Then we calculate the pH of the solution:

pH = -log [H⁺]

pH = -log (0.0467 M)

pH = 1.33

5 0

2 years ago

A chemist has 60ml of a 3M NaCl solution. He needs to dilute it so the Molarity is 1M NaCl. How much water does he need to add?

REY [17]

Answer:

80 ml the right answer

Explanation:

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3 years ago

Does the following compound contain a polyatomic ion? Na2SO4<br> Yes<br> No

seropon [69]

The answer is yes I believe so.

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2 years ago