Question

Your biology professor rips off the label on a solution container and dumps it. He tells you one of his TA’s must not have paid attention in class, because the dilution in the NaCl container is wrong. He needs you to make a 500ml 0.5M solution from a 2M stock bottle quickly. 1. How many mL of 2M NaCl need to be added to make 500ml of a 0.5 M solution? (2pt) 2. How many grams of NaCl are in a 500ml of 0.5M solution? (NaCl=58.44g/mol) (2pt)

Answer 1

1) stock concentration (M1)= 2 M

final volume (V2)= 500 mL

final concentration (M2)= 0.5 M

volume of stock solution required (V1)=?

M1V1=M2V2

V1=M2V2/M1

=(0.5500)/2

= 125 mL

volume of 2M NaCl need to be added to make 500ml of a 0.5 M solution = 125 mL

2) molarity= number of moles/volume of solution in litres

1L= 1000 mL

500 mL= 500/1000=0.5 L

0.5= number of moles/0.5

number of moles=0.50.5

=0.25

number of moles= mass in gram/gram molecular mass

molar mass of NaCl=58.44g/mol

0.25= mass in gram/58.44

mass in gram= 0.2558.44

= 14.61 gram

grams of NaCl are in a 500ml of 0.5M solution= 14.61