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NNADVOKAT [17]
3 years ago
8

PLS HELP ! 5.00 mL of a stock solution, containing 0.200 M of Na3PO4 was pipetted into a 25.00 mL volumetric flask and made up t

o the calibration mark with deionised water. A serial dilution was carried out for another two times to obtain the final solution of desired concentration. Calculate the concentration of the final solution, express in ppm (by volume).
Chemistry
1 answer:
JulijaS [17]3 years ago
4 0

Answer:

262 ppm of Na₃PO₄

Explanation:

In a dilution, the concentration of the initial solution is decreased. When you take 5.00mL of the solution that is diluted to 25.0mL The solution is diluted 25/5 = <em>5 times</em>

If you make another two serial dilutions the final solution wil decrease its concentration 5*5*5 = 125 times

As original solution containing 0.200 M of Na3PO4, the final solution will have a concentration of:

0.200M / 125 = <em>1.6x10⁻³M</em>

Molarity is defined as the ratio between moles and liters. 1.6x10⁻³ moles of Na3PO4 in 1L are:

1.6x10⁻³mol ₓ (164g/mol) = 0.262g Na₃PO₄ / L

Assuming density of Na3PO4 as 1g/mL the concentration of the solution is:

0.262mL Na₃PO₄ / L

As 1mL = 1000μL:

262μL Na₃PO₄ / L

μL of solute per L of solution is equal to ppm, that means the solution has:

<h3>262 ppm of Na₃PO₄</h3>

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The key to any dilution calculation is the dilution factor

The dilution factor essentially tells you how concentrated the stock solution was compared with the diluted solution.

In your case, the dilution must take you from a concentrated hydrochloric acid solution of 18.5 M to a diluted solution of 1.5 M, so the dilution factor must be equal to

DF=18.5M1.5M=12.333

So, in order to decrease the concentration of the stock solution by a factor of 12.333, you must increase its volume by a factor of 12.333by adding water.

The volume of the stock solution needed for this dilution will be

DF=VdilutedVstock⇒Vstock=VdilutedDF

Plug in your values to find

Vstock=25.0 L12.333=2.0 L−−−−−

The answer is rounded to two sig figs, the number of significant figures you have for the concentration od the diluted solution.

So, to make 25.0 L of 1.5 M hydrochloric acid solution, take 2.0 L of 18.5 M hydrochloric acid solution and dilute it to a final volume of 25.0 L.

IMPORTANT NOTE! Do not forget that you must always add concentrated acid to water and not the other way around!

In this case, you're working with very concentrated hydrochloric acid, so it would be best to keep the stock solution and the water needed for the dilution in an ice bath before the dilution.

Also, it would be best to perform the dilution in several steps using smaller doses of stock solution. Don't forget to stir as you're adding the acid!

So, to dilute your solution, take several steps to add the concentrated acid solution to enough water to ensure that the final is as close to 25.0 L as possible. If you're still a couple of milliliters short of the target volume, finish the dilution by adding water.

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Answer:

Approximately 6.81 × 10⁵ Pa.

Assumption: carbon dioxide behaves like an ideal gas.

Explanation:

Look up the relative atomic mass of carbon and oxygen on a modern periodic table:

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  • O: 15.999.

Calculate the molar mass of carbon dioxide \rm CO_2:

M\!\left(\mathrm{CO_2}\right) = 12.011 + 2\times 15.999 = 44.009\; \rm g \cdot mol^{-1}.

Find the number of moles of molecules in that 41.1\;\rm g sample of \rm CO_2:

n = \dfrac{m}{M} = \dfrac{41.1}{44.009} \approx 0.933900\; \rm mol.

If carbon dioxide behaves like an ideal gas, it should satisfy the ideal gas equation when it is inside a container:

P \cdot V = n \cdot R \cdot T,

where

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Rearrange the equation to find an expression for P, the pressure inside the container.

\displaystyle P = \frac{n \cdot R \cdot T}{V}.

Look up the ideal gas constant in the appropriate units.

R = 8.314 \times 10^3\; \rm L \cdot Pa \cdot K^{-1} \cdot mol^{-1}.

Evaluate the expression for P:

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Apply dimensional analysis to verify the unit of pressure.

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