Question

Solid sodium reacts violently with water, producing heat, hydrogen gas, and sodium hydroxide. How many molecules of hydrogen gas are formed when 48.7 g of sodium are added to water?
2Na + 2H2O --> 2NaOH + H2

Show your work.

Answer 1

@ParthKohli ? @Mertsj ? Can you help?

Answer 2

balanced reactions tell us the ratios between the pieces we use and the pieces we form, but it doesn't tell us MASS ratios, it tells us ratios of QUANTITY. To predict the amount of product we need to know the number of moles that the problem gives us. Can you turn 48.7g of Na into moles of Na?

Answer 3

is it 2.12 moles of Na?

Answer 4

@JFraser ?

Answer 5

@dumbcow @ghazi @hba ? Can someone please help me???

Answer 6

(1) convert to moles
(2) use coefficients to determine how many moles of product you have

eg. aA + bB -> cC

moles of A/a = moles of C/c

if you have 1 mole of A and want to find moles of C, then:

moles of C=1*c/a

(3) once you have the moles, covert to molecules knowing that 1 mole = avogadros number

Answer 7

I'm lost...

Answer 8

do step by step and post it, il check it

Answer 9

is it converted to moles = 2.12 ?

Answer 10

yes

Answer 11

Ok so what do I do next? I'm sorry I'm really confused and I need to figure this out.

Answer 12

use the 2nd step i outlined

Answer 13

How do I use the coefficients to determine how many moles I have though??

Answer 14

I'm just really really confused..

Answer 15

look at the step i posted and follow what i did

Answer 16

I know that but I'm obviously confused by what you did and I need help figuring it out....

Answer 17

it's simple algebra, il give you another example:

N2 + 3 H2 → 2 NH3

if you have 3 moles of N2 and you want to find how many moles of NH3 you can make then:

\[\frac{ n _{N _{2}} }{ 1}=\frac{ n _{NH _{3}} }{ 2 }\]

\[\frac{3}{ 1}=\frac{ n _{NH _{3}} }{ 2 }\]

solve of moles of NH3

Answer 18

solve for* not of

Answer 19

I'm still confused

Answer 20

well try it by following the example and post it, il rectify your mistakes

Answer 21

I don't know how to try it! I don't understand it when it's not the actual numbers I'm using... My brain doesn't function that way.. Can you maybe just at least set it up for me and I can try and see if I can get it then??

Answer 22

if i set it up I'm basically answering the question for you, so i'm not going to do that.
but lets try this, what are the coefficients of each of the substances in question?

Answer 23

2Na is 2, 2H2O is 2, 2NaOH is 2, ?

Answer 24

well sure, but what are the ones they are asking about? hint: re-read the question

Answer 25

Hydrogen gas and water?

Answer 26

"How many molecules of hydrogen gas are formed when 48.7 g of sodium are added to water?"

they are asking about hydrogen and sodium, not water

Answer 27

now, what are the coefficients?

Answer 28

2 and 1?

Answer 29

Oh wait. hold on

Answer 30

2 ,2, and 1?

Answer 31

why are there 3 different ones? there is only 2 substances in question: hydrogen gas and sodium

Answer 32

oh sorry. 2 and 1.

Answer 33

which one is which

Answer 34

1 of hydrogen gas and 2 of sodium

Answer 35

okay, so divide each one by it's coefficient and set them equal to each other

Answer 36

How do you divvide Na by 2?

Answer 37

you divide the moles by the coefficient

Answer 38

I don't understand. I've been working on this homework for 3 hours.. my brain hates me

Answer 39

how many moles of Na did 48.7 g give you?

Answer 40

2.12?

Answer 41

so divide that by the coefficient

Answer 42

1.06?

Answer 43

set it up as a ratio though

Answer 44

do the same for H2, and set them equal to each other, and POST IT

Answer 45

How do I set it as a ratio?

Answer 46

a ratio is a fraction

Answer 47

oh. ok

Answer 48

0.5=1/2

Answer 49

53/50 = 121/5 .....? I did that totally wrong didn't i

Answer 50

okay, you're overcomplicating this, you're merely supposed to write:

\[\frac{ moles of Na }{ coefficient }\]

Answer 51

Omg. See, this is why I suck at school.

Answer 52

it's not that you "suck", you just have to think about what you're trying to do and really think and anaylize it

Answer 53

ok so would it be: 2.12 mol Na/2 = 24.2 mol H2/1 ?

Answer 54

well yes and no.

you don't know how many moles of H2 you have so that is your unknown,

so 2.12/2=x/1

x=moles of H2

Answer 55

Ok so is x=mol of H2 the answer?

Answer 56

no, they're asking for the amount of molecules, so whatever you get for the moles of H2, multiply by avogadros number

Answer 57

......... I'm lost again

Answer 58

okay how many moles of H2 gas do you have?

Answer 59

x

Answer 60

NO, 24.2

Answer 61

NO, x

Answer 62

x is not a number, you're solving for x from the equation above.

Answer 63

2.12/2=x/1

what is the value of x?

Answer 64

24.2?

Answer 65

how did you get that?

Answer 66

Uh. I don't remember..

Answer 67

well do it again and find it because that previous answer is incorrect

Answer 68

You're no help at all.

Answer 69

lol okay then

Answer 70

maybe it's you that is dense, i tried simplifying things to a grade 2 level, clearly you don't have the brain for science, ingrate.

Answer 71

Just for the record guys and gals reading this that got to this point,
Once you get 1.06 for 2.12/2=x/1 which is pretty much 2.12 divided by 2. You should multiply it by Avogadro's number to get your final answer.
Right? @aaronq

Answer 72

yes