Calculating Water Volume from Molar Concentration of NaCH3COO

  • Thread starter Nicole1998
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In summary, the conversation discussed the calculation of the volume of water used in a solution of 2.8 g of NaCH3COO with a resulting concentration of 4.3 * 10^-2 M. The equation c = n/V was used, with the resulting volume of 0.79 L. However, it was unclear whether this was the volume of the solution or just the water. Various methods for approximating the volume of water were discussed, such as assuming the volume of water was the same as the volume of the solution or using the density of sodium acetate to estimate the volume. The density of a 0.043 M sodium acetate solution at 20°C was also mentioned as 1.000
  • #1

Homework Statement


2.8 g of NaCH3COO is dissolved into an unknown volume. The resulting concentration produced is 4.3 * 10-2 M, what volume of water was used?

Homework Equations


c = n/V

The Attempt at a Solution


I[/B] calculated molar mass of the NaCH3COO as 82.0 g/mol, which is 0.034 mol. I then used the c = n/V equation.

4.3 * 10-2 M = 0.034 mol / V
V = 0.79 L

Where I am confused now is if that is the volume of the solution, or of the water? I think it's the volume of solution, and am not sure how to calculate the water.
 
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  • #2
Nicole1998 said:

Homework Statement


2.8 g of NaCH3COO is dissolved into an unknown volume. The resulting concentration produced is 4.3 * 10-2 M, what volume of water was used?

Homework Equations


c = n/V

The Attempt at a Solution


I[/B] calculated molar mass of the NaCH3COO as 82.0 g/mol, which is 0.034 mol. I then used the c = n/V equation.

4.3 * 10-2 M = 0.034 mol / V
V = 0.79 L

Where I am confused now is if that is the volume of the solution, or of the water? I think it's the volume of solution, and am not sure how to calculate the water.

You are correct that molarity refers to moles solute per volume of solution. You could estimate a volume of water in a number of ways:
Estimate that the volume contribution from the sodium acetate is small compared to the volume of the water and say that the volume of water is the same as the volume of solution. You could estimate the total volume if you estimated that the total volume was the combined volume of sodium acetate plus volume of water (you could calculate the volume of sodium acetate if you looked up the density of the sodium acetate in the CRC Handbook. If you wanted to calculate the volume of water exactly, you would need to know the partial molar volumes of each species at this concentration.

Now, think about how much precision you have in your numbers, and think about which method of approximation is appropriate. [The percent error in the weight of sodium acetate is 3% and the percent error in the molarity is 2% -- the percent error in the volume will be 3%]. V = 790 mL +/- 30 mL

Since the uncertainty in the volume is pretty big, what kind of assumptions would you be safe making in order to calculate the volume of water used?
 
  • #3
If you knew the density of a 0.043 molar solution of NaCH3COO in water, then you would know the total number of grams of solution in 0.79 L. Since there are 2.8 gm of NaCH3COO, the rest would be water. You could then look up the density of water at that temperature, and determine the volume of the water before the solution was mixed.

Chet
 
  • #4
At 20°C density of the 0.043 M sodium acetate solution is 1.0000 g/mL (that's a little bit higher than pure water, 0.9982 g/mL at the same temperature).

In general, you can safely assume density of most solutions to be 1 g/mL. That's not exactly true, but it is better than nothing when you have no other data. And before you will be forced to use density tables, you will probably get some intuition about when it matters.
 
  • #5


Your calculation is correct. The volume calculated is the volume of the final solution, which includes both the NaCH3COO and the water used to dissolve it. In order to determine the volume of water used, you would need to know the initial volume of water before the NaCH3COO was added. If the initial volume of water is unknown, it is not possible to calculate the volume of water used.
 

1. How do I calculate the water volume from molar concentration of NaCH3COO?

To calculate the water volume from molar concentration of NaCH3COO, you will need to use the formula V = n/C, where V is the volume of water (in liters), n is the number of moles of NaCH3COO, and C is the molar concentration of NaCH3COO (in moles per liter). You can find the number of moles of NaCH3COO by multiplying the molar concentration by the volume of the solution in liters.

2. What units should I use for molar concentration and water volume?

Molar concentration is typically measured in moles per liter (mol/L), while water volume can be measured in liters (L) or milliliters (mL). It is important to ensure that the units for both molar concentration and water volume are consistent in order to get an accurate calculation.

3. Can I use any type of solution to calculate water volume from molar concentration?

Yes, you can use any type of solution to calculate water volume from molar concentration. However, it is important to make sure that you are using the correct molar concentration for the specific solution you are working with. For example, a solution of NaCH3COO will have a different molar concentration than a solution of HCl.

4. How does temperature affect the calculation of water volume from molar concentration?

Temperature can affect the calculation of water volume from molar concentration because it can impact the volume of the solution. As temperature increases, the volume of the solution will also increase. Therefore, it is important to use the correct temperature when measuring the volume of the solution in order to get an accurate calculation.

5. Can I use this calculation to determine the water volume in a chemical reaction?

Yes, this calculation can be used to determine the water volume in a chemical reaction. Simply use the molar concentration of the reactant (such as NaCH3COO) in the formula V = n/C, where n is the number of moles of the reactant and C is the molar concentration. This will give you the amount of water needed for the reaction based on the given molar concentration.

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