Concentration questions (1 Viewer)

[Fortian09]

Hi all,

I'm doing concentration questions and i kind of need some help with some stuff on water.

the questions are.

1) What volume of

a) 10M hydrochloric acid isneeded to make 5L of 0.1M solution? (I dont get what to do in this question...)

b) 18M sulfuric acid is needed to prepare 2L of 2M sulfuric acid? (I dun get this one either...)

2) 10mL of 18M sulfuric acid was added to water to make 150mL of solution. What is its molarity? (what do i need to look for?)

and whats the empirical formula of hydrazine?

 

[minijumbuk]

1.
a) They are asking what amount of the concentrated HCl is required to dilute it to 5L of 0.1M

Moles of HCl in diluted solution = 5 x 0.1
= 0.5 mol
Therefore 0.5 mol is needed from the 10M HCl
Therefore volume = 0.5/10
= 0.05L
= 50 mL of the 10M HCl

There is actually a quicker way to do this. Use the formula c₁v₁ = c₂v₂
So 10c₁ = 0.1 x 5
c₁ = 0.5/10
= 0.05L or 50 mL required for the dilution
This is basically the first method I've shown you, but kind of a shortcut method.

b) Same as a). Again, use the formula.
18 x v₁ = 2 x 2
v₁ = 4/18
= 0.22L
= 220 mL of the 18M sulfuric acid is needed for the dilution.

2. Molarity is the concentration of solutions, measured by mole per litre of water (mol/L, or commonly known as "M")

Moles of sulfuric acid = 0.01 x 18
= 0.18 moles
Therefore a solution of 150 mL would have a molarity of:
0.18 mol / 0.15 L = 1.2 mol/L, or 1.2 M.

I have no idea what hydrazine is, but a quick wiki search gave me its molecular formula to be N₂H₄
Empirical formula is the ratio of each element, thus the empirical formula of hydrazine is NH₂
Note that this formula just tells you that for every 1 N atom, there are 2 H atoms. It does not actually mean 2 H atoms bonded to 1 N atom.

 

[Fortian09]

hmm y is the chemistry forum so quiet?

anyway more qns

'M' stands for mol/L right?

 

[Continuum]

Yeah M stands for molarity, which is measured in mol/L.

 

[kooltrainer]

this guys a fortian

 

[Fortian09]

yup a fort street idiot

 

[kooltrainer]

me too

 

[Fortian09]

You go fort street?
yr 12 yeah?

 

[benji6667]

a) 10M hydrochloric acid is needed to make 5L of 0.1M solution?

Quick formula for concentration questions: C1V1 = C2V2
C1 = 10M
C2 = 0.1M
V1 = unknown
V2 = 5L

10 * V1 = 0.1 * 5
V1 = (0.1 * 5) / 10
V1 = 0.05L Or 50mL

So 50mL of 10M HCl is needed to make 5L of 0.1M HCl solution

The longer method of doing this is by calculating the moles.

C = n / V
n(Hcl) = C * V
n(Hcl) = 0.1 * 5
n(Hcl) = 0.5

So we need 0.5 moles of HCl to make a 5L solution of 0.1M HCL, the next step is to find what volume of 10M HCL will give us 0.5 moles

C = n / V
V = n / C
V = 0.5 / 10
V = 0.05L or 50mL

EDIT: I didn't even check if someone else had already helped this person, oops!

 

[minijumbuk]

Just a careless mistake, but to avoid confusion, benji: 0.05L is 50 mL, not 15 mL

 

[benji6667]

Just a careless mistake, but to avoid confusion, benji: 0.05L is 50 mL, not 15 mL

hey, whered that 1 come from

 

[Continuum]

hey, whered that 1 come from

Ninja much?

You edited your post.

 

[minijumbuk]

C = n / V
V = n / C
V = 0.5 / 10
V = 0.05L or 15mL

I WIN! =D
Haha.

 

[benji6667]

I WIN! =D
Haha.

:angry::angry::angry:fffffffffffffffffffffffffff