Question

@surry99

Answer 1

ok to solve this you need to know charges

Answer 2

do you know what double replacement means for a reaction?

Answer 3

yes.

Answer 4

great so lets look at RbOH...do you know what the charge is on either Rb or OH?

Answer 5

It appears to be neutral...

Answer 6

no the entire compound RbOH is neutral but Rb has a positive charge and OH has a negative charge...it is an ionic compound.

Answer 7

Oh, duh, right. :)

Answer 8

cause in double-replacement reactions the positive ions switch

Answer 9

good

Answer 10

how do you know that Rb is the one with the positive charge?

Answer 11

and not vice versa

Answer 12

it is on the left in the formula, the negative species is on the right

Answer 13

that is convention

Answer 14

okay. you can continue now. :)

Answer 15

So do you know either the charge on Rb or OH or...
can we figure it out from the periodic table

Answer 16

I think you may have been asked to memorize the name and charge on OH

Answer 17

i thought you said the charage was negative...

Answer 18

it is I just have not indicated it yet...

Answer 19

It is called hydroxide and has a charge of -1, OH-

Answer 20

ok

Answer 21

did you know that?

Answer 22

sounds familiar, I'm sure I've learned it. I don't think my brain can handle memorizing too many things. just how i am. :)

Answer 23

So, if we have the formula RbOH and OH is -1....what must be the charge on Rb?

Answer 24

+1

Answer 25

Great...notice how you applied conservation of charge to RbOH to get that...

Answer 26

haha, more like applying math common sense

Answer 27

LOL...but it i conservation of charge.

Answer 28

Just gotta teach my head to equilvate math concepts with chemistry concepts...

Answer 29

Suppose you didn't know OH was -1, how might you have been able to get eh charge on Rb? Grab your periodic table please...

Answer 30

Hmmm.i don't know. I have my periodic table and cannot figure it out

Answer 31

alkali metal?

Answer 32

I will help...see the Rb is in column number 1 with elemental hydrogen etc?

Answer 33

no, wait...electrons

Answer 34

right? the electrons and protons to figure out teh charge

Answer 35

yes, all the elements in that column like to give up one electron and therefore have a charge of +1 as cations.

Answer 36

ah, i see. don't know why i didn't think of it

Answer 37

before now

Answer 38

ok, so Rb is +1 and OH is -1...
what about H3PO4...what is the charge on each hydrogen

Answer 39

hint: it is in the same column as Rb...

Answer 40

+1

Answer 41

great so what must be the charge on PO4?

Answer 42

+2

Answer 43

oops, sorry -1

Answer 44

try again ...

Answer 45

each hydrogen is +1 and there are 3 of them and only one PO4...

Answer 46

-3

Answer 47

yes...now with all the charges figured out I think you can see the answer to the double replacement reaction...oui?

Answer 48

yeah. just a switcheroo

Answer 49

yes indeed...

Answer 50

wait...why is it not B...C isn't balanced...

Answer 51

B cant be correct because the first product for instance RbPO4 assumes a -1 charge on phosphate but we determined it is -3.

Answer 52

ah. ok. but how come it isn't balanced...a mistake?

Answer 53

ah...if they had balanced the equation (including reactants) you could have got the answer without doing all the work we did...which was what they are testing

Answer 54

so they did it purposely...sneaky.

Answer 55

one last one, then i have to take the test. it's getting late

Answer 56

ok

Answer 57

ok