ssNake's Chemistry [u2] Q's

[REBORN]

Lol I got 1.2L aswell....the answer is 0.08L.

How about my 3rd Q regarding Lead Nitrate?

Q: A lead nitrate solution has a molarity of 0.5M. How many moles of Lead nitrate in 500mL of solution?

I got 0.5?

[b^3]

c=n/v
n=cv
=0.5*0.5
=0.25mols

[tony3272]

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And I disagree with their answer here...

Q: A lead nitrate solution has a molarity of 0.5M. How many moles of Lead nitrate in 500mL of solution?

I got 0.5?

I got 0.25mol.

[Lasercookie]

Q: A lead nitrate solution has a molarity of 0.5M. How many moles of Lead nitrate in 500mL of solution?

I got 0.5?

n = cV
n = 0.5M * 0.500L
n = 0.25 mol
?

edit: damn, too slow.

[REBORN]

fml I thought it was asking for nitrate ions so I x2  >.>

thanks boys....

with the dilution Q they're working is: 35g per L is = to 7g/200mL therefore 7x200 = 5xv2 therefore v2 = 280ml therefore water to be added is 280-200 = 80mL = 0.08L....

Is that right or b^3 (1.2L?)

The original Q:

Q: Household bleach contains 35g of NaClO per L of bleach. What vol of water must be added to 200mL of bleach to change the concentration of NaClO to 5g/L?

[b^3]

i don't know how they went from 35g/1000ml to 7g/20ml, its dividing by 1000/20=50so it would be 35/50=0.7g/20ml so I think they are wrong, what does everyone else think?

EDIT: The 20 is a type right, let me have another look.

[REBORN]

my bad...yeah typo...

I'm still confused :/

[b^3]

I still think I'm right because from that we can tell that there is 7g in the 200ml, so the concentrationw e want is 5g so c=m/v so 5=7/v
meaning v=7/5=1.4L
then take the 0.2 gives 1.2L
Someone else please check this just in case.

[Lasercookie]

Note: I think you have to convert to M, but it may not be nessecary, can someone verify this?

I converted to M and I also ended up getting 1.2L

Molar Mass of NaClO = 74.5
c1 = 35/74.5 = 0.469M
c2 = 5/74.5 = 0.067M
v1 = 0.200L

v2 = (0.469M*0.200L)/(0.067M) = 1.4L
1.4L - 0.2L = 1.2L

I think I converted from g/L to M right?

Also 35g/1000mL simplifies to 7g/200mL, not 7g/20mL. I think the textbook error came from missing that extra zero. 

If you use that method, then 7 * 200mL = 1400mL.
1400mL - 200mL = 1200mL = 1.2L

[b^3]

yeh same that I did, looks right too, must be wrong in the book, at least it's not like the methods 3&4 checkpoints where half of the answers are wrong.

[REBORN]

But what's WRONG with their WORKINGS?

all of us got 1.2L but I'm struggling to find what they've differently? :S

btw what's with all your workings?.....

All I did was 35x200 = 5x therefore x=1400 therefore 1400-1200 = 1200mL = 1.2mL

[Lasercookie]

But what's WRONG with their WORKINGS?

all of us got 1.2L but I'm struggling to find what they've differently? :S

btw what's with all your workings?.....

All I did was 35x200 = 5x therefore x=1400 therefore 1400-1200 = 1200mL = 1.2mL

I used the dilution formula. Pretty much the same thing, you're just using different variables.

I think the textbook error came from simplifying 35/1000 to 7/20 instead 7/200. 

[REBORN]

I used the dilution formula too?

I just left it in g/L and mL whereas you guys went to n/L for some reason?

and nah that was my typo....they gave 7g/200mL

[b^3]

Not exaclty, they did 7*200 but 7 is not the concentration, 35g/l is the concentration, 7g is the amount of mass in 200ml, not the concentration, thats why they are wrong.

Use 35 and it works

35*200/5=v2
=1400ml take the 200ml =1200ml =1.2L Q.E.D

[REBORN]

There we go....

We're right. woohoo.

/[u2] chem checkpoints fail!