Question

@Hoslos Can you help with more??

Answer 1

t

Answer 2

Sure, why not?

Answer 3

For the first exercise, use the formula I gave you before mol=mass/molar mass. Make mass subject of the formula=mol*molar mass and for the second column make the ratio of mass:mol, in such way that you get n:1

Answer 4

Should I try one for you or we move on to the next exercise?

Answer 5

For the second exercise you again use the mol formula, but for part 1, simply find the molar mass, using the masses from your periodic table. Having

Answer 6

8*C+9*1+14 +16*2.
For part 2, use mol=mass/molar mass, where you mass is 0.5g and molar mass is the one you calculated in the first part.
For part 3, simply multiply your value of moles by 3.

Answer 7

on the first part i dont understand by getting n:1 @Hoslos

Answer 8

and for the first part can you help me through one??

Answer 9

@JFraser please help me understand this i got the first column on the table but i dont understand how to do the rest

Answer 10

finding the formula weight (or the molar mass) gets you the RATIO of mass to one mole.

as a separate example, the molar mass of HCl is 36.5g/mol. One mole of HCl will weigh 36.5grams, that's what the molar mass tells us.

If you have more than one mole of HCl, it will weigh more than 36.5g. The ratio can be used as a conversion fraction to convert from grams to moles and back again.

Answer 11

ok nevermind the first column is confusing too...im soo lost

Answer 12

1?

Answer 13

The formula weight is found by taking the masses of all the pieces in that formula and adding them all together.

Answer 14

so H is 1 + cl is 35 so that equals 36...i understand that part but after i get that # how do i get formula weight g/mol is it this #

Answer 15

adding the masses together gets you the formula weight, so that is the answer for the second column

Answer 16

ok now how do i get # of moles??

Answer 17

if you're given a mass, and you have the formula weight, you use the formula weight as a conversion fraction

Answer 18

If I have 45g of HCl, how many moles is that?

Answer 19

ok but in the first row there isnt a mass

Answer 20

i have formula weight and # of moles

Answer 21

it doesn't matter, the process works in both directions

Answer 22

if you HAVE mass, you can FIND moles. If you HAVE moles, you can FIND mass

Answer 23

ok so if i have moles i divide, and if i have mass i multiply??

Answer 24

\[45g \space HCl * \frac{1 mole \space HCl}{36.5g \space HCl}\]

Answer 25

see how the fraction is actually the formula weight, and it cancels the mass and replaces them with moles?

Answer 26

ok how did you get 45?

Answer 27

i came up with it, 45g of HCl

Answer 28

ok i might understand this better if i tryed the first one
i have 58.4g/mol (weight formula)
and 0.14 for moles...what do i do??

Answer 29

you HAVE moles, and you WANT grams. start a conversion fraction starting with 0.14 moles

Answer 30

\[0.14 moles * \frac{something}{something \space else}\]

Answer 31

the formula mass goes in the fraction, but it depends on whether you put it "right-side up" or "upside-down"

Answer 32

so it goes on the bottem???

Answer 33

the "it" that goes on the bottom is the MOLES so that when you multiply units on top and bottom they cancel

Answer 34

so the mass goes on top and the moles goes on bottom\[0.14moles * \frac{36.5g \space HCl}{1 mole \space HCl}\]

Answer 35

so i just multiply 0.14 and 36.5 right?? i dont have to do a fraction thing if it will always cancel right
so i multiply with moles and formula weight, and divide with formula weight and mass

Answer 36

you really are using a fraction every time, because you have to make sure the units cancel properly.

Answer 37

the short way, you're basically correct.

If you have mass and want moles, divide the (mass/FW)

If you have moles and want mass, multiply (moles * FW)

Answer 38

thanks thats all i needed

Answer 39

can you check my first problem to make sure i am doing it right..
58.4g/mol (FW) 0.14 (moles) and i got 8.176 on the mass

Answer 40

if you have 0.14 moles of a substance that has a formula weight of 58.4g, then yes, you have 8.176g of that substance.