Question

In a soluble solution, is water always a reactant?

Answer 1

I am currently studying the acid-base chapter in my textbook, and I don't understand how to set up the equation so that it is applicable to finding the pH.

How do I set this up?
And what steps do I take to solve for all of the concentrations needed to find the pH?

1)What is the pH of a 0.50 M(molarity) solution of sodium nitrite at 25.0 (degrees) Celsius?

The Ka is given for HNO2 at 25 (degrees) Celsius: 4.5 x 10^-4.

Answer 2

Wheres Wolfe when you need him? -.-

Answer 3

TToTT

Answer 4

@e.mccormick You know this one?

Answer 5

I have a quiz tomorrow~ please recruit help!!!

Answer 6

It''s been too long since I have done these

Answer 7

I tried every other site I could think of...and it's pretty traumatic because Google has failed me...and that's pretty bad...ToT *cry face*

Answer 8

If this question is going to be on the quiz then it has to be something that was taught to you or atleast in your textbook. Try checking through your notes or go through your textbook.

Answer 9

All I remember is \(\large pH = -\log_{10}[H^+]\) or I guess it's \([H_3O^+]\)

Answer 10

I flipped through the notes and the textbook as well, but it bever tells me what to put on what side of the equation.... I mean, there is like, HA-->H+A but I went through some of the equations and they're different sometimes...

Answer 11

oh yes this is more complicated because it's a weak acid, oh dear even more that I don't remember too well.

Answer 12

TToTT It's more complicated because it's a weak acid??? How~?

Answer 13

hang on a sec, lemme work on it .-.

Answer 14

well you need to use the pKa, it's not just a simple complete dissociation as in a strong acid. but urgh I was googling stuff but omg I am too distant from chemistry to remember all this @_@

Answer 15

Thank you~~~ *tears of gratefulness*

Answer 16

Wait hold on. If it's a strong acid/base, that means that with water, it would dissociate? And then if it's anything weak(HA/HB) then I have to use pKa?

Answer 17

just tagging our chemistry expert :) @chmvijay

Answer 18

The powerful summoning of the ChemMaster~ ^^

Answer 19

or...maybe no?

Answer 20

Reposting this question so it's answered ^^: If it's a strong acid/base, that means that with water, it would dissociate? And then if it's anything weak(HA/HB) then I have to use pKa?

Answer 21

So, you mainly need in the numerical, right?

Answer 22

yeah...? Uhm, like setting up the equation and then finding the concentrations of the species that are not given...
and also, since in this one specifically, it gives the NaNO2 concetration of .5 Molarity, instead of giving me the HNO2 or something like that...

Answer 23

NaNo2 + H2O ----> HNO2 + NaOH
First off that will be the equation ,
and we need to find pH of NaNo2 or HNO2?:S

Answer 24

Ohhh hold on, since we can say that Na=an observer ion(?Right?) then the OH is left alone, find the pOH, and subtract from 14?

Answer 25

Hmm yea !

Answer 26

hmm... seems that way... but then what was @kirbykirby saying about the dissociation thing?

Answer 27

and is the H2O always going to be on the reactants side?

Answer 28

Yeah Its sodium nitrate solution , so YES!

Answer 29

"solution"

Answer 30

wait yes to the first or second?

Answer 31

question

Answer 32

I mean the H20 will always be on the reactant side

Answer 33

ohhhh YESHHHHHH oh my gosh the world just lit up a little~
and back to what @kirbykirby said...If it's a strong acid/base, it would dissociate? And then if it's anything weak(HA/HB) then I have to use pKa?

Answer 34

Yes if we r using strong acid/base then only it will dissociate otherwise we have to use pKa!

Answer 35

H2o is strong enough to cause dissociation , so we dont need to use pKa

Answer 36

Wow Cyber...I never knew you had all dis knowledge o_O

Answer 37

hmmm...so how to tell what to use...like, for this equation, I wouldn't even be able to use Ka=([H] {A])/(HA)...............

Answer 38

hehe shad :P

Answer 39

And there's 4 types of Titration curve problems, so...

Answer 40

see our equation is
NO2- + H2O <--> HNO2 + OH-

Answer 41

Kb = [HNO2][OH-]/[NO2-]

Answer 42

Ka= (products)/(reactants) and it involves H

Answer 43

But Ka is already given to us in the question isnt it? Why do u need to find it

Answer 44

oh, if I wanted to find the molarities of any of the species in the formula...but I suppose I don't really need that....

Answer 45

Would you mind too awfully if I asked another question? Kind of related~

Answer 46

Lol No , Shoot ~

Answer 47

thanks~ uhm, so:
The question is: 0.5 mole of nitrous acid and 0.1 mole of potassium nitrite are added to enough water to make 1.0 liter of solution at 25(degrees Celsius)...
and the first part is to get the pH,
and the second part is: Calculate the pH after 0.010 mole of HCl is added

Answer 48

do not consider water in the equation :)

Answer 49

oh ok...hmmm...

Answer 50

but I would use it when calculating molarity?

Answer 51

yup :)

Answer 52

and I wouldn't add any of the other's volume because they are virtually insignificant...right?

Answer 53

oh hoold on never mind the total is 1 haha

Answer 54

so first thing is that potassium is an observer ion?

Answer 55

wait would HNO2 and KNO2 go on the same side??? the reactants side>??? OoO nooooo...

Answer 56

Yeah!

Answer 57

They wont be on same side

Answer 58

And Pottasium is an observer ion

Answer 59

sooo.... NO2+ H2O <--->HNO2 + OH?

Answer 60

Yea!

Answer 61

And so what happens to the equation when HCl is thrown in?

Answer 62

HCl + KNO2 ---> KCl + HNO2

Answer 63

Is there a water anywhere in there?

Answer 64

Nope

Answer 65

Water all around my island

Answer 66

hmmm... oh snap...the Ka is for HNO2, but...it's still products/reactants...hmm... does it matter where exactly the HNO2 is in the equation???

Answer 67

hmm no, HNO2 will always be in the product side .-.

Answer 68

right...but then this one equation keeps tripping me up... Ka=[(H)(A)]/(HA)

Answer 69

Ok What exactly is tripping u up? :P what in this equation?

Answer 70

http://scramlinged.com/resources/Notes+on+Weak+Acids+and+Bases.pdf
the equation at the top, just in case my weird typing was hard to look at ^^
uhm, it's the fact that making the HA and the H2O not on the same side...the fact that there is a OH instead of an H~ or an H3O

Answer 71

Because then... if I wanted to, could I use this equation?: HNO2+H2O-----> NO2+H3O

Answer 72

hmm actually yea , u cant use this equation .-.

Answer 73

OoO why? uhoh.

Answer 74

cos HA and H20 cant be on the same side, Anion reacts with H20 to make HA .-. jeez

Answer 75

And... how can I find the pH of that second equation HCl+KNO2---> KCl+HNO2 if there's no water...???

Answer 76

wait if Cl and K are deemed observer ions, that would make sense...but then...how did you decide to use KNO2? was it becasue it's a product of the first equation?

Answer 77

KNO2 is in the solution? then we add Hcl into it? did that make sense? Thats how we used it

Answer 78

ohhhhhhh oh my gosh hahaha and so you know of a way to eassily memorize the main strong acids? That's something major that I haven't found out how to memorize quite right yet... :|

Answer 79

basically hydrides of halogens and p block elements are strong acids..........the bigger the period of the atom attached to Hydride , the stronger the acid

Answer 80

HI (halogen attached), >HNO3(oxygen and nitrogen , P-block)

Answer 81

did that make sense? :P

Answer 82

sort of? Whats a hydride?

Answer 83

compounds of hydrogen (with a H in it) for e.g (H)Cl , NH3

Answer 84

ohhhh haha and so H with anything in the p block would make a good strong acid?

Answer 85

Yeah ! and as the period number increases more acidic it will be! some acids even have 2 p-block elements attached to em for eg HNO3

Answer 86

But If we have lower P-block period elemets like C then acid will be kinda weak for e.e HCN

Answer 87

C??? but isnt that the same period and only one proton short of N???

Answer 88

Oh wait no i meant Period lol

Answer 89

Yeah its one proton short thats why its weak :P

Answer 90

and btw therer is an excpetion H2s is kinda weak , it is because it hydrogen bonds and doesnt give out H+ ions

Answer 91

u will learn all this stuff in inorganic chemistry or chemical bonding chapters

Answer 92

So...generally, it has to also be something that could stand on it's own just fine? like HF, and the H can detacha dnt the F has to become F2?

Answer 93

for the record HF is weak acid too cos it has strong Bond Between H and F due to small sizes and its tough to remove H+ ion

Answer 94

i d sugest to give a reading to P=Block elements chapter or Chemical Bonding Chapter

Answer 95

that will explain all of these concepts

Answer 96

HCL and HI are strong acids cos they can easily release H+ ion and they will make Cl2 ,and I2 respectively

Answer 97

hmmm so...things that are bigger in period, yet the more easily they are able to lose protons, the better. And then they are most...or alll? in the p-block