Which Method for Calculating Moles is More Effective?

[supernova1203]

Do both of these methods for calculating the number of moles work?

we've learned a new method recently which i prefer over the older method for current curriculum

n₁=c₁v₁

n for number of moles, c for concentration 1 and v for volume 1
and the old method is

# of moles = mass/molar mass

does the first method work?

 

[Borek]

You are asking to compare apples and oranges. How are you going to use the second method to calculate number of moles in 1 L of 0.3M solution, how are you going to use first method to calculate number of moles in 6g of carbon? Both approaches are correct, but they are used in completely different situations.

Besides, what you call a "new method" is just a rearranged molar concentration definition (which you probably should know by now):

$$C = \frac n V$$

solve for n.

 

[supernova1203]

Also there is another question, I am certain there's a typo here, if not see if this makes sense (attachment)

 

[Borek]

Formula used to calculate number of moles of HCl is wrong, but otherwise result is correct.