Question

You have a solution made of 300 grams of ethanol (C2H5OH) and 500 grams of water. What is the mole fraction of ethanol in this solution?
(Points : 1)
0.19 M

0.81 M

0.19

0.81

Answer 1

If you want to make 0.5 L of a 0.01 M solution of bromine (Br2) in water, how much bromine would you need?

(Points : 1)
0.8 grams

0.8 moles

1.6 grams

1.6 moles



Question 2.2. Which of the following statements is the correct definition of molarity?
(Points : 1)
number of moles of solvent/liter solution

number of grams of solvent/liter solution

number of moles of solute/liter solution

number of grams of solute/liter solution

Answer 2

the last one is \[M=\frac{ moles of solute }{ Liters of solution }\]

Answer 3

so its C

Answer 4

yes.

Answer 5

Thank you

Answer 6

for the other two, its just about the same concepts. do you know how to use the molar mass to convert to moles?

Answer 7

no i dont

Answer 8

okay well this should help:

\[grams of substance*\frac{ moles of substance }{ molar mass of substance }\]

Answer 9

do you know what the molar mass is?

Answer 10

the mass of a substancd

Answer 11

the mass of a substance per one mole. you get the molar mass by using the periodic table of elements

Answer 12

ok thanks

Answer 13

if you use the equation i gave you to convert, then those other two problems should be a breeze.

Answer 14

alright i will if i need any help ill ask :)

Answer 15

ok

Answer 16

I dont know the first one but for the second one i got B is that righ?

Answer 17

very close but not quite.

\[M=\frac{ mol solute }{ L solution }\]

Answer 18

so....\[0.01=\frac{ x moles }{ .5 L }\]

Answer 19

x moles = 0.005 moles Br2

Answer 20

but that isnt one of the options so we need to go farther.

(0.005 mol)(159.808g/1 mol)

"mol" cancels and we are left with 0.8 grams Br2

Answer 21

Ohhh okay. what about the other one

Answer 22

use the molar mass to convert both substances to moles first.

Answer 23

Ethanol:

(500g)(1 mol/46.07g)

10.85 mol ethanol

Answer 24

can you do the other one?

Answer 25

no i dont understand it

Answer 26

its thesame thing that i just did. with ethanol

Answer 27

with the what? sorry im confused

Answer 28

sometimes its easier to see it written.... does this help?

Answer 29

yes i skipped over the water part thats why i didnt understand

Answer 30

okay. so do you know what a mole fraction is?

Answer 31

no

Answer 32

\[\frac{ moles-of-substance }{ total-number-of-moles }\]

Answer 33

so... we want this:
\[\frac{ moles-of-ethanol }{ (moles-of-ethanol)+(moles-of-water) }\]

Answer 34

so the answer is .19m

Answer 35

yes!

Answer 36

Yayyy thank you

Answer 37

do you understand it? like maybe with a bit of practice, you could do it on your own next time?

Answer 38

yea i think so

Answer 39

good. :)