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telo118 [61]
3 years ago
13

In the titration of 50.0 mL of HCl of unknown concentration, the phenolphthalein indicator present in the colorless solution tur

ns pink when 26.5 mL of 0.130 M Ca(OH)2 is added. Show the calculation of the molarity of the HCI.
Chemistry
1 answer:
KIM [24]3 years ago
7 0

Answer:

The molarity of HCl is 0.138 M

Explanation:

The titration reaction is as follows:

2HCl + Ca(OH)₂ → CaCl₂ + 2H₂O

When no more HCl is left, the small excess of Ca(OH)₂ added will cause the pH to rise and the indicator will turn. At this point, the number of moles of Ca(OH)₂ added will be the same as half the number of moles of HCl since 1 mol Ca(OH)₂ reacts with 2 moles HCl. Then:

At the endpoint:

moles Ca(OH)₂  = moles HCl / 2

Knowing the number of moles of Ca(OH)₂ added, we can calculate the number of moles of the acid:

mol Ca(OH)₂ = Volume added * concentration of Ca(OH)₂

mol Ca(OH)₂ = 0.0265 l * 0.130 mol/l = 3.45 x 10⁻³ mol Ca(OH)₂

The number of moles of HCl will be:

mol HCl = 2 * 3.45 x 10⁻³ mol = 6.89 x 10⁻³ mol HCl

This number of moles was present in 50.0 ml, then, in 1000 ml:

mol of HCl in 1000 ml = 6.89 x 10⁻³ mol HCl * (1000ml / 50ml) = 0.138 mol

Then:

Molarity HCl = 0.138 M

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A 3.452 g sample containing an unknown amount of a Ce(IV) salt is dissolved in 250.0 mL of 1 M H2SO4. A 25.00 mL aliquot is anal
Olenka [21]

Answer:

The weight percent in the sample is 17,16%

Explanation:

The dissolution of the Ce(IV) salt provides free Ce⁴⁺ that reacts, thus:

2Ce⁴⁺ + 3I⁻ → 2Ce³⁺ + I₃⁻

I₃⁻ + 2S₂O₃²⁻ → 3I⁻ + S₄O₆²⁻

The moles in the end point of S₂O₃⁻ are:

0,01302L×0,03247M Na₂S₂O₃ = 4,228x10⁻⁴ moles of S₂O₃²⁻.

As 2 moles of S₂O₃⁻ react with 1 mole of I₃⁻, the moles of I₃⁻ are:

4,228x10⁻⁴ moles of S₂O₃⁻×\frac{1molI_{3}^-}{2molS_{2}O_{3}^{2-}} = <em>2,114x10⁻⁴ moles of I₃⁻</em>

As 2 moles of Ce⁴⁺ produce 1 mole of I₃⁻, the moles of Ce⁴⁺ are:

2,114x10⁻⁴ moles of I₃⁻× \frac{2molCe^{4+}}{1molI_{3}^-} =  <em>4,228x10⁻⁴ moles of Ce(IV)</em>.

These moles are:

4,228x10⁻⁴ moles of Ce(IV)×\frac{140,116g}{1mol} = 0,05924 g of Ce(IV)

As was taken an aliquot of 25,00mL from the solution of 250,0mL:

0,05924 g of Ce(IV)×\frac{250,0mL}{25,00mL} =0,5924g of Ce(IV) in the sample

As the sample has 3,452g, the weight percent is:

0,5924g of Ce(IV) / 3,452g × 100 = <em>17,16 wt%</em>

I hope it helps!

3 0
3 years ago
In the coal-gasification process, carbon monoxide is converted to carbon dioxide via the following reaction: CO (g) + H2O (g) ⇌
Oksana_A [137]

Answer: Equilibrium constant is 0.70.

Explanation:

Initial moles of  CO = 0.35 mole

Volume of container = 1 L

Initial concentration of CO=\frac{moles}{volume}=\frac{0.35moles}{1L}=0.35M

Initial moles of  H_2O = 0.40 mole

Volume of container = 1 L

Initial concentration of H_2O=\frac{moles}{volume}=\frac{0.40moles}{1L}=0.40M

equilibrium concentration of CO=\frac{moles}{volume}=\frac{0.18moles}{1L}=0.18M [/tex]

The given balanced equilibrium reaction is,

                            CO(g)+H_2O(g)\rightleftharpoons CO_2(g)+H_2(g)

Initial conc.            0.35 M       0.40M       0     0

At eqm. conc.    (0.35-x) M   (0.40-x) M   (x) M    (x) M

The expression for equilibrium constant for this reaction will be,

K_c=\frac{[CO_2]\times [H_2O]}{[CO]\times [H_2O]}

K_c=\frac{x\times x}{(0.40-x)(0.35-x)}

we are given : (0.35-x)= 0.18

x = 0.17

Now put all the given values in this expression, we get :

K_c=\frac{0.17\times 0.17}{(0.40-0.17)(0.35-0.17)}

K_c=0.70

Thus the value of the equilibrium constant is 0.70.

5 0
2 years ago
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