Describe how you would prepare 250.0 mL of a 0.500 M solution of NaCl by using apparatus found in a chemistry lab.
5 answers
did you try putting it in a 600mL beaker?
no
The definition of molarity is
M = #mols/Liter of solution.
If you want to do this by math (instead of reasoning), you first plug in 0.5 for M and 0.250 for L and calculate #moles.
0.5=moles/0.250 L
moles NaCl = 0.5 x 0.250 = 0.125 moles.
1 mole NaCl = approximately 58.5 grams. So 0.125 moles NaCl is ......
Or by reasoning, we want 0.5 mole for 0.5 M in 1 L and divide that by 4 for only 1/4 of a liter (250 mL). So we want 1/4 of 1/2 = 1/8 of a mole (or 0.125 mol).
But this isn't the tricky part. The tricky part is telling the prof HOW to prepare the solution. You will want to take 1/8 mole NaCl (about 7 grams or so), place it in a 250 mL volumetric flask, add a little water, swirl until all of the NaCl is dissolved, then make to the mark with water. That will prepare 0.5 M solution in a 250 mL volumetric flask. (Note that I DID NOT say to add about 7 grams NaCl to 250 mL water.).
M = #mols/Liter of solution.
If you want to do this by math (instead of reasoning), you first plug in 0.5 for M and 0.250 for L and calculate #moles.
0.5=moles/0.250 L
moles NaCl = 0.5 x 0.250 = 0.125 moles.
1 mole NaCl = approximately 58.5 grams. So 0.125 moles NaCl is ......
Or by reasoning, we want 0.5 mole for 0.5 M in 1 L and divide that by 4 for only 1/4 of a liter (250 mL). So we want 1/4 of 1/2 = 1/8 of a mole (or 0.125 mol).
But this isn't the tricky part. The tricky part is telling the prof HOW to prepare the solution. You will want to take 1/8 mole NaCl (about 7 grams or so), place it in a 250 mL volumetric flask, add a little water, swirl until all of the NaCl is dissolved, then make to the mark with water. That will prepare 0.5 M solution in a 250 mL volumetric flask. (Note that I DID NOT say to add about 7 grams NaCl to 250 mL water.).
write the steps something like this
1. Place 0.125 moles NaCl (7.305 grams) in a 250 mL volumetric flask, add some water, swirl to dissolve all of the NaCl, then make to the mark with water. You PROBABLY should round the 7.305 g to 7.31 grams.
4 answers