Calculating 0.5M NaCl in 500mL Water

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SUMMARY

To prepare a 0.5M NaCl solution in 500mL of water, one must dissolve 29.25 grams of NaCl, calculated using its molecular weight of 58.5 g/mol. The conversion from volume to moles is critical, as 0.5M indicates 0.5 moles of NaCl per liter of solution. Therefore, for 0.5L, the correct amount of NaCl is determined by the equation: 0.5 moles x 58.5 g/mol = 29.25 grams. It is essential to understand that the number of moles of NaCl is dependent on the volume of the solution, not the amount of water alone.

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Homework Statement


How many grams of NaCl (molecular weight=58.5g mole^-1) would you dissolve in water to make a 0.5M NaCl solution with 500mL final volume?



Homework Equations





The Attempt at a Solution

Since, 1 L of 58.5g NaCl is equal 1M I used this to firstly convert 500ml into liters which is 0.5L and then I said that half 0f 58.5g is 27.25g NaCl and this will give me 0.5 M in 0.5L of water.
 
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No, 0.5 mole in 0.5L is not 0.5M.
 
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So, does the number of moles in NaCl change depending on the amount of water?
 
mmedin01 said:
So, does the number of moles in NaCl change depending on the amount of water?

[STRIKE]Yes.[/STRIKE] (Misread that "moles in NaCl"...)
Here's one way to look at it:

0.5 M NaCl = 0.5 mol NaCl/1 L solution = ? mol NaCl/0.5 L solution

For the two fractions to be equal, what number does the numerator have to be?
 
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mmedin01 said:
So, does the number of moles in NaCl change depending on the amount of water?

There is no such thing as "number of moles in NaCl". There is either "number of moles of NaCl" or "number of moles of NaCl in the given volume of the solution".
 
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