Chemistry question (can someone check if I did it right)

Phosphoric acid is a tribasic acid
What is the mass of Ca(OH)2 that completely neutralises 100cm3 of 0.100moldm-3 phosphoric acid?

A 0.49g
B 0.74g
C 1.11g
D 2.22g

So I found the moles of phosphoric acid: 100 x (0.100/1000) = 0.01moles

Mr of Ca(OH)2 = 74.1

Mass of Ca(OH)2 = 0.01 x 74.1 = 0.741 = 0.74g

Idk if this is right ??

Reply 1

Pigster

20

Original post by Unknownn1.x

Phosphoric acid is a tribasic acid
What is the mass of Ca(OH)2 that completely neutralises 100cm3 of 0.100moldm-3 phosphoric acid?

A 0.49g
B 0.74g
C 1.11g
D 2.22g

So I found the moles of phosphoric acid: 100 x (0.100/1000) = 0.01moles

Mr of Ca(OH)2 = 74.1

Mass of Ca(OH)2 = 0.01 x 74.1 = 0.741 = 0.74g

Idk if this is right ??

You need to balance the equation and use the molar ratio of reactants in your calculation.

Where did you get this Q from?

Reply 2

Pigster

20

Original post by Unknownn1.x

It’s the 2020 paper

And what do u mean I’m a bit confused

Have you balanced the equation for the reaction that is taking place?

I am just surprised that you've had the 2020 paper given out, it isn't meant to be public, yet.

Reply 3

Unknownn1.x

OP

8

Original post by Pigster

Have you balanced the equation for the reaction that is taking place?

I am just surprised that you've had the 2020 paper given out, it isn't meant to be public, yet.

So I need to do an equation, can you explain it to me in detail because I’m getting muddled up

Reply 4

Pigster

20

Original post by Unknownn1.x

So I need to do an equation, can you explain it to me in detail because I’m getting muddled up

Part of the point of the Q is that it is testing whether you can balance the equation.

To tell you the equation would be to ruin that part of the Q.

Reply 5

scoobiedoobiedoo

12

Original post by Unknownn1.x

So I need to do an equation, can you explain it to me in detail because I’m getting muddled up

You got it right don't worry so when you do this question you write out the equation 🙂 then you work out the number or moles in phosphoric acid and the Mr of calcium hydroxide. The balanced equation should show you the ratio of moles which will help determine the calcium hydroxide moles luckily for you the ratio was 1:1:1:1: so moles didn't change aha so when you worked out mass you got it right 😉 here's my working out sorry if you still don't get it I tried making it as clear as possible

Reply 6

Sonnysingh22

8

Original post by scoobiedoobiedoo

You got it right don't worry so when you do this question you write out the equation 🙂 then you work out the number or moles in phosphoric acid and the Mr of calcium hydroxide. The balanced equation should show you the ratio of moles which will help determine the calcium hydroxide moles luckily for you the ratio was 1:1:1:1: so moles didn't change aha so when you worked out mass you got it right 😉 here's my working out sorry if you still don't get it I tried making it as clear as possible

Thank you so much! I appreciate it! :smile:

Reply 7

Shefalix

11

Original post by scoobiedoobiedoo

You got it right don't worry so when you do this question you write out the equation 🙂 then you work out the number or moles in phosphoric acid and the Mr of calcium hydroxide. The balanced equation should show you the ratio of moles which will help determine the calcium hydroxide moles luckily for you the ratio was 1:1:1:1: so moles didn't change aha so when you worked out mass you got it right 😉 here's my working out sorry if you still don't get it I tried making it as clear as possible

I dont think thats balanced because there's one calcium on the left and 2 on the right??

Reply 8

Ljdf0072

12

Hi,
The equation above isn't fully balanced yet,
When you balance it, it should be
2 H3PO4 + 3 Ca(OH)2 = 6H2O + Ca3(PO4)2
Then when you have the moles of phosphoric acid, you divide by 2 and times by 3 to get moles of Ca(OH)2.
Hope this helps! :smile:

Reply 9

Alicia Sanchez

8

Original post by Unknownn1.x

Phosphoric acid is a tribasic acid
What is the mass of Ca(OH)2 that completely neutralises 100cm3 of 0.100moldm-3 phosphoric acid?

A 0.49g
B 0.74g
C 1.11g
D 2.22g

So I found the moles of phosphoric acid: 100 x (0.100/1000) = 0.01moles

Mr of Ca(OH)2 = 74.1

Mass of Ca(OH)2 = 0.01 x 74.1 = 0.741 = 0.74g

Idk if this is right ??

answer is C but is don't know how