Question

Potassium hyroxide and phosphoric acid react to form potassium phosphate and water according to the equation:

3KOH + H3PO4 --> K3PO4 + 3H2O

Determine the starting mass of each reactant if 63.5 g of K3PO4 is produced and 84.8 g of H3PO4 remains unreacted.

What is the starting mass of KOH?

What is the starting mass of H3PO4?

Answer 1

Alright so we are going to ignore the mass that did not react for now and use the nass that did react to determine how much KOH it took to cause the reaction.

Answer 2

Wait i read that wrong let me make some quick rearrangements lol

Answer 3

Alright

Answer 4

Okay so we are going to use the amount of KOH produced to determine how much H3PO4 reacted.

Answer 5

*K3PO4

Answer 6

So 63.5g

Answer 7

yeah im doing my work right now but what we want to do is start with the 63.5 g of K3PO4 and convert it to KOH in g

Answer 8

\[\frac{ 63.5 g K3PO4 }{ }*\frac{ 1 mole K3PO4 }{ 212 g K3PO4 }*\frac{ 3 mole KOH }{ 1 mole K3PO4 }*\frac{ 56 kg KOH }{ 1 mole KOH }*\frac{ 1000 g }{ 1 kg }\]

Answer 9

that would give you the starting g of KOH. and you do the same thing for H3PO4 but you will add 84.58 to whatever you get for H3PO4 because that amount did not react. And the conversion give you the amount that did react.

Answer 10

I got 50320.754 for KOH

Answer 11

What would I use with the H3PO4? Would it be the H2O?

Answer 12

KOH is 50.32 i messed up on the conversion lol see i used Kg thats supposed to be gram so ignore that last step where you multiplied by 1000.

And no H2O is just bonus information you dont really need it for H3PO4 use K3PO4 also its just that the ratios will be different when its mole over mole.

Answer 13

Do you think you could set up the one for H3PO4 or do you want me to do it for you

Answer 14

I'll try it

Answer 15

Alright ill be here

Answer 16

84.8 g x (1 mol H3PO4/ 97.994) x ( 1 mol K3PO4/ 1 mol H3PO4) x ( 56.10g K3PO4 / mol H3PO4)

Answer 17

No , You want to find out how much H3PO4 it took to create 56.1 g of K3PO4. To do this you want to find out how much H3PO4 is made from 56.1 g of K3PO4.
STart with 56.1 g of K3PO4 and convert it to H3PO4 in grams.

Answer 18

and its 63.5 not 56.1

Answer 19

Sorry

Answer 20

no its fine just remember to basically do the problem backwards if youre looking for H3PO4 start with the K3PO4

Answer 21

\[\frac{ 63.5 g K3PO4 }{ }*\frac{ 1 mole K3PO4 }{ 212 g K3PO4 }*\frac{ 1 mole H3PO4 }{ 1 mole K3PO4 }*\frac{ 98 g H3PO4 }{ 1 mole H3PO4 }\]

Answer 22

so would it basically be like the K3PO4 except replace the KOH with H3PO4?

Answer 23

yes that is right. Youre just switching what youre converting to so the only thing that changes is the molar mass and possibly the ratio of moles

Answer 24

that will give you the amount of H3PO4 that reacted.

Answer 25

29.35377

Answer 26

yes so what it the starting mass of H3PO4 and KOH?

Answer 27

You need to add 84.8 to it right?

Answer 28

Yes! I wanted to make sure you understood that!

Answer 29

So I got 114.153

Answer 30

Yes that is the answer for K3PO4, what about for KOH?

Answer 31

50.32

Answer 32

Yes Sir!

Answer 33

Nice

Answer 34

Thanks for the help. I wish I could give you extra medals. You've really helped me today.

Answer 35

yes sir anything else?

Answer 36

Not right now. I'm going through right now making sure I didn't skip anything.

Answer 37

alright

Answer 38

oh and you're welcome! lol and it is cool i use this as a break from my homework it is fun!

Answer 39

What's your homework?

Answer 40

And you would make a really good chemistry tutor if you're not already. I know my school pays people to tutor.

Answer 41

Its Calculas but more specifically optimization right now lol. and thank you lol and i would tutor but im a cashier at dollar tree :P

Answer 42

Yikes. I avoided that stuff like the plague. Then again I'm not the best at math.

Answer 43

Yeah lol i do not like it either! just one more semester of math after this and im done with it for life lol

Answer 44

I thought that too but then learned how much math is in chemistry then I got physics too. Bleh. I got my actual math classes out of the way though. Do you have a major?

Answer 45

omg i forgot about physics. but I have never taken a physics class in my life so that might make it harder too lol. And yeah im a biochemistry major what about you?

Answer 46

I haven't taken a physic course a day in my life either. I'm a pre-vet major.

Answer 47

to be honest i don't even know what Phsyics is lol and im a pre-med