# Difference between diluting and adding

## Homework Statement

1. Place 20.0 g NaOH(s) in a flask and dilute to 1.00 L with water.
2. Place 20.0 g NaOH(s) in a flask and add 1.00 L of water.

How exactly do these two statements differ? Wouldn't adding 1.00L of water to 20.0g of NaOH dilute it anyways?

none?

## The Attempt at a Solution

[/B]
Which of the following methods correctly describes the preparation of 1.00 L of an aqueous solution of 0.500 M NaOH?

a. Place 0.500 g NaOH(s) in a flask and dilute to 1.00 L with water.
b. Place 0.500 g NaOH(s) in a flask and add 1.00 L of water.
c. Place 20.0 g NaOH(s) in a flask and dilute to 1.00 L with water.
d. Place 20.0 g NaOH(s) in a flask and add 1.00 L of water.
e. Place 40.0 g NaOH(s) in a flask and add 500 g of water.

I was able to narrow it down to c and d (the two statements above), but I'm not sure what's the difference between the two.

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## Answers and Replies

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Borek
Mentor
Is the final concentration in both cases identical?

@Borek — I don't think I am told anything like that...

Concentration = mole / liters. In both cases I have 1L and 20g (which can easily be converted to moles by using the atomic molar mass), don't I?

epenguin
Homework Helper
Gold Member
The solid occupies a volume, or makes a difference to the volume of liquid that it dissolves in, so in which case do you know at the end exactly the g/L ?

@epenguin —I'm not sure if it should be obvious by now, but I'm not sure bc in both cases the solid is already in the flask (and so occupies volumes)?

epenguin
Homework Helper
Gold Member
OK In which case at the end of do you know exactly the volume of the solution?

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Borek
Mentor
When you fill up to 1L - what volume do you end up with?

When you add something to 1 L of water - is the final volume 1 L, or not?

## Homework Statement

1. Place 20.0 g NaOH(s) in a flask and dilute to 1.00 L with water.
2. Place 20.0 g NaOH(s) in a flask and add 1.00 L of water.

How exactly do these two statements differ? Wouldn't adding 1.00L of water to 20.0g of NaOH dilute it anyways?

none?

## The Attempt at a Solution

[/B]
Which of the following methods correctly describes the preparation of 1.00 L of an aqueous solution of 0.500 M NaOH?

a. Place 0.500 g NaOH(s) in a flask and dilute to 1.00 L with water.
b. Place 0.500 g NaOH(s) in a flask and add 1.00 L of water.
c. Place 20.0 g NaOH(s) in a flask and dilute to 1.00 L with water.
d. Place 20.0 g NaOH(s) in a flask and add 1.00 L of water.
e. Place 40.0 g NaOH(s) in a flask and add 500 g of water.

I was able to narrow it down to c and d (the two statements above), but I'm not sure what's the difference between the two.
By definition, Molarity is the No. of moles of solute per unit volume of solution (in L). What inference do you draw from it?

Merlin3189
Homework Helper
Gold Member