The Student Room Group
Reply 1
Widowmaker


What mass of calcium hydroxide would be needed to deal with 1000 dm3 of sulphur dioxide?


This can be done using moles. From the equation given, you know that 1 mol Ca(OH)2 is needed to react completely with 1 mol of SO2.

1)Work out how many moles in 1000dm3 of SO2 (remember it is a gas so under standard conditions 24dm3 is 1 mol)

2)Therefore the same number of moles of Ca(OH)2 are needed

3)Mass of Ca(OH)2 needed can be worked out by multiplying this number of moles by the molar mass of Ca(OH)2 which you can work out by the atomic masses given on the periodic table.

Hope that helps
oxymoron
This can be done using moles. From the equation given, you know that 1 mol Ca(OH)2 is needed to react completely with 1 mol of SO2.

1)Work out how many moles in 1000dm3 of SO2 (remember it is a gas so under standard conditions 24dm3 is 1 mol)

2)Therefore the same number of moles of Ca(OH)2 are needed

3)Mass of Ca(OH)2 needed can be worked out by multiplying this number of moles by the molar mass of Ca(OH)2 which you can work out by the atomic masses given on the periodic table.

Hope that helps

Yes I did that, it's jus that all the answers given with the questions are wrong and I just wanted to check if I was right.

No of moles = volume/24 = 1000/24 = 41.67 moles.
Mass of Ca(OH)2 = 41.67 x molar mass
= 41.67 x 74 = 3083 grams.

Is this correct?
Reply 3
Sounds right to me. What answer is given in question?
oxymoron
Sounds right to me. What answer is given in question?

324.3g
Reply 5
Widowmaker
324.3g


Can't see how they got that ... I would stick with your answer
There is another question which I though was quite tough for AS but oh well.
Can you check it for me?

Hardness in water is caused by dissolve calcium compounds. When heated some of these break down and deposits calcium carbonate as follows:

Ca(HCO3)2 → CaCO3 + H2O +CO2

This builds up as 'fur' on the inside of boilers. It can be removed by reaction with hydrochloric acid.

What mass of calcium carbonate would be produced from 10000 dm3 of water containing 0.356 g of calcium hydrogen carbonate per dm3 of water and what volume of 10M HCl would be needed to remove the solid calcium carbonate from the inside of the boiler?

Calculations
Part 1
Ca(HCO3)2 → CaCO3 + H2O + CO2
10000dm3
0.356gdm^-3

Therefore mass of Ca(HCO3)2 = 10000 x 0.356 = 3560g

No of moles = mass/molar mass = 3560/162 = 21.98 moles

mass of CaCO3 = 21.98 x molar mass = 21.98 x 100 = 2198 grams

Part 2
2HCl + CaCO3 --> H2CO3 + CaCl2
2198g
21.98 moles

Therefore no of moles of HCl = 2 x 21.98 = 43.95

No of moles = (concentration x volume (cm3) )/1000
No of moles = (10 x V)/1000
43.95 = 0.01V
V = 43.95/0.01 = 4395cm3 = 4.395dm3
oxymoron
Can't see how they got that ... I would stick with your answer

Yeah I asked my teacher and he said he thought that most of the answers were wrong.
Your calculations seem fine... what textbook did you use or where did you get the question from?
Fade Into Black
Your calculations seem fine... what textbook did you use or where did you get the question from?

I have no idea. My teacher just produced a scheme of lessons with these questions in and he just puts a list of answers at the end.
Reply 10
You got the molar mass of Ca(HCO3)2 wrong. It is 162 not 98.

That gives the same answers as given in the book.

Hope that helps :smile:
oxymoron
You got the molar mass of Ca(HCO3)2 wrong. It is 162 not 98.

That gives the same answers as given in the book.

Hope that helps :smile:

Ah, so it is, thankyou.
Reply 12
Widowmaker

72.66 = 0.01V
V = 72.66/0.1 = 726.6cm3 = 0.7266dm3



Also a mistake there as you changed the 0.01 to a 0.1 giving a factor of 10 error in your answer.
oxymoron
Also a mistake there as you changed the 0.01 to a 0.1 giving a factor of 10 error in your answer.

see my edited post. It does work thankyou.
Sorry, just one more that i'm stuck on.

When nitrogen reacts with hydrogen in the Haber Process only 17% of the nitrogen is converted to ammonia. What volume of nitrogen and what volume of hydrogen would be needed to produce 1 tonne of ammonia? ( 1 tonne = 1 x 10^6 g)

Okay, so the reaction is.
N2 + 3H2 --> 2NH3
Mass of ammonia = 1000000g

No of moles of ammonia = mass/molar mass = 1000000g/17 = 58823.53 moles
No of moles of H2 = 88235.3 moles
No of moles of N2 = 29411.76 moles

No of moles = Volume/molar volume = V(dm^3)/24

So for N2 88235.3 x 24 gives volume = 2.12 x 10^6 dm^3 of Nitrogen but the answer says 4.15 x 10^6 dm^3.

I don't know how to finish it, where does the 17% value come in to the equation?
Gosh, how many hours of work do you do a day................ :smile:
Fade Into Black
Gosh, how many hours of work do you do a day................ :smile:

Tonnes. I am way behind on Chemistry.
Reply 17
Widowmaker
Sorry, just one more that i'm stuck on.

When nitrogen reacts with hydrogen in the Haber Process only 17% of the nitrogen is converted to ammonia. What volume of nitrogen and what volume of hydrogen would be needed to produce 1 tonne of ammonia? ( 1 tonne = 1 x 10^6 g)

Okay, so the reaction is.
N2 + 3H2 --> 2NH3
Mass of ammonia = 1000000g

No of moles of ammonia = mass/molar mass = 1000000g/17 = 58823.53 moles
No of moles of H2 = 88235.3 moles
No of moles of N2 = 29411.76 moles

No of moles = Volume/molar volume = V(dm^3)/24

So for N2 88235.3 x 24 gives volume = 2.12 x 10^6 dm^3 of Nitrogen but the answer says 4.15 x 10^6 dm^3.

I don't know how to finish it, where does the 17% value come in to the equation?


First of all ... for N2 the moles you got was 29411.76 (you are using the H2) value in the last sentence.

When you get your answer for the volume, that is how much reacts. You need to divide that by 0.17 to get back to the volume you need to use as only 17% of the N2 you put in is reacting

so 29411 x 24 / 0.17 should give you the answer
oxymoron
First of all ... for N2 the moles you got was 29411.76 (you are using the H2) value in the last sentence.

When you get your answer for the volume, that is how much reacts. You need to divide that by 0.17 to get back to the volume you need to use as only 17% of the N2 you put in is reacting

so 29411 x 24 / 0.17 should give you the answer

Oh yeah, sorry i'm tired.