Question

Chem: Calculate the moleseeded to prepare each
a. 1.0 L of a 3.0M NaCl solution
b. 0.40 L of a 1.0M KBr solution
c. 125 mL of a 2.0 M MgCl2 solution

Answer 1

the correct answers are
a. 3 moles
b. .40 moles
c. .25 moles
but i don't know how to get them!

Answer 2

a. 3.0M=3moles/liter(1liiter)=3moles
b. 1.0M=1moles/liter(.4liter)=.4 moles
b. 2.0M=2moles/liter(.125liters)=.25moles

Answer 3

the 3.0M numbers give you how many moles there are per L, so if you multiply by how many liters there are you get the amount of moles

Answer 4

Just to clarify on what physopholy said. You need to cancel L to get the moles:
\[1.0 L * 3.0 M = 1.0 L * 3.0 \frac{moles}{L}=3.0 moles NaCL\]
\[0.40L*1.0M=0.40L*1.0\frac{moles}{L}=0.40 moles KBr\]
\[125ml*2.0M=0.125L*2.0\frac{moles}{L}=0.25 moles MgCl_2\]
Note you have to keep the correct Significant figures which is 2 in each case.