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kumpel [21]
3 years ago
12

A phosphate buffer solution (25.00 mL sample) used for a growth medium was titrated with 0.1000 M hydrochloric acid. The compone

nts of the buffer were sodium monohydrogenphosphate and sodium dihydrogenphosphate. The first endpoint occurred at a volume of 10.32 mL, and the second occurred after an additional 18.62 mL was added, for a total volume of 28.94 mL. What was the total concentration of phosphate (in any form) in the buffer?
Chemistry
1 answer:
AysviL [449]3 years ago
7 0

Answer:

0,07448M of phosphate buffer

Explanation:

sodium monohydrogenphosphate (Na₂HP) and sodium dihydrogenphosphate (NaH₂P) react with HCl thus:

Na₂HP + HCl ⇄ NaH₂P + NaCl <em>(1)</em>

NaH₂P + HCl ⇄ H₃P + NaCl <em>(2)</em>

The first endpoint is due the reaction (1), When all phosphate buffer is as NaH₂P form, begins the second reaction. That means that the second endpoint is due the total concentration of phosphate that is obtained thus:

0,01862L of HCl×\frac{0,1000mol}{L}= 1,862x10⁻³moles of HCl ≡ moles of phosphate buffer.

The concentration is:

\frac{1,862x10^{-3}moles}{0,02500L} = <em>0,07448M of phosphate buffer</em>

<em></em>

I hope it helps!

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1. Which of the following pairs of factors affects the solubility of a particular substance? (1 point)
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<h2>Question no 1:</h2><h3>Answer:</h3>

The correct answer is option A which is temperature and the nature of solute and solvent

<h3>Explanation:</h3>
  • The solubility of a substance is its ability to dissolve in a particular solution.
  • Solubility is highly dependent on the temperature and nature of solute and solvent.
  • It is directly proportional to the temperature. As we increase the temperature, the solubility of substantial increases but for the exothermic reactions, solubility is inversely proportional to temperature.
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<h2>Question no. 2</h2><h3>Answer:</h3>

The correct answer is option B which is a large amount of solute.

<h3>Explanation:</h3>
  • A concentrated solution contains the maximum amount of solute which can be dissolved in the solvent.
  • For example, in water sugar solution concentrated solution will contain a large amount of sugar dissolved in water without the addition of heat.
  • In dilute solution, there is a small amount of solute.
<h2>Question no. 3:</h2><h3>Answer:</h3>

The correct answer is option B which is molarity × liters of solution.

<h3>Explanation:</h3>

Molarity of a solution is the total number of moles of solute per unit volume of solution.

Its formula is:

             Molarity = Number of moles of the solute/volume of solution in liters.

    A number of moles of solute =  Molarity × Volume of the solution.

So the number of moles of solute is equal to the molarity and volume of solution. Hence correct option is B.

<h2>Question no 4.</h2><h3>Answer:</h3>

The correct answer is option D. Molarity of the dilute solution = 0.81 M

<h3>Explanation:</h3>

Given data:

        initial volume = V1 = 225 mL = 0.225 L

        Initial molarity = M1 = 0.80M

        Final volume =  V2 = 1 L

        Final molarity  = M2 = ?

Solution:

It is the dilution of the stock solution and the formula is given below:

V1M1 = V2M2

M2 = V1.M1/V2

By putting values in the formula:

M2 = 0.225 × 0.8/1

M2= 0.18

So the final molarity of the solution will be 0.18 M. Hence the correct answer is option D.

<h2>Question no. 5</h2><h3>Answer:</h3>

The correct answer is option B which is supersaturation.

<h3>Explanation:</h3>
  • Colligative properties of the solution are the properties which are not dependent on the number of particles of the solute in the solution.
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The correct answer is option B/C, "which disrupts crystal formation of the solvent".

<h3>Explanation:</h3>
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The correct answer is option D which is 142.

<h3>Explanation:</h3>

<u>Given data:</u>

Volume of solution = 167 ml

Percentage of solution = 85%

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Percentage of solution ( v/v) = volume of solute/volume of solution × 100

The volume of solute = percentage × volume of solution/100

By putting values in above formula:

Volume of alcohol = 85 × 167/100 = 141.95 ml

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To obtain molarity of HNO₃ we need to know both moles and volume of this acid. The volume is (27,71±0,05) mL and to calculate the moles it is necessary to obtain the Na₂CO₃ moles and then convert these to HNO₃ moles, thus:

0,9585 g of Na₂CO₃ × ( 1 mole / 105,988 g) =

9,043×10⁻³ mol Na₂CO₃ × ( 2 moles of HNO₃ / 1 mole of Na₂CO₃) = 1,809×10⁻² moles of HNO₃

Molarity is moles divide liters, thus, molarity of HNO₃ is:

1,809×10⁻² moles / 0,02771 L = 0,6527 M of HNO₃

The absolute uncertainty of multiplication is the sum of relative uncertainty, thus:

ΔM = 0,6527M× (0,0007/0,9585 + 0,001/105,988 + 0,05/27,71) =

0,6527 M× 2,54×10⁻³ = 1,7×10⁻³ M

Thus, molarity of HNO₃ solution and its absolute uncertainty is:

(0,653±0,002) M of HNO₃

I hope it helps!

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