Calculations Involving Volumes of Gases (1 Viewer)

[Sam.]

I just wanted to check if you guys get the same answers as me for these problems:

2CO(g) + O2(g) → 2CO2(g)

1. Calculate the volume of oxygen required at 25oC and 1.00 atmosphere for the combustion of 28g of carbon monoxide.

C2H5OH + 3O2 → 3H2O + 2CO2

2. If 98L of CO2 is formed at 25oC and 1.00 atmosphere pressure, calculate the mass of ethanol used in the reaction.
3. Calculate the volume of liquid water formed when the products are condensed at 25oC and 1.00 atmosphere.

2H2S(g) + 3O2(g) → 2SO2(g) + 2H2O(g)

4. If 8g of oxygen is consumed by a sample of hydrogen sulfide, what volume of H2S reacts at 0oC and 1.00 atmosphere pressure?

2NH4Cl(s) + Ca(OH)2(s) → 2NH3(g) + 2H2O + CaCl2(s)

5. If 107g of ammonium chloride reacts fully with excess Ca(OH)2, what volume of ammonia is produced at 0oC and 1.00 atmosphere pressure.

An answer to any of them would help.

 

[pLuvia]

2CO(g) + O2(g) → 2CO2(g)

1. Calculate the volume of oxygen required at 25oC and 1.00 atmosphere for the combustion of 28g of carbon monoxide.

28/MW_CO = 0.99964....

0.99964..... x MV(24.79) = 24.78 L (2dp)

C2H5OH + 3O2 → 3H2O + 2CO2

2. If 98L of CO2 is formed at 25oC and 1.00 atmosphere pressure, calculate the mass of ethanol used in the reaction.

98/24.79 = 3.9532....moles

Number of moles of ethanol used: 1
Number of moles of CO₂ formed: 2

.: 3.9532.... x 1/2 = 1.9766...moles

Mass of ethanol = 1.9766... x 46.08 = 91.06 g (2dp)

Let the others do the other ones

 

[Sam.]

Great, that's what I got too (minus rounding errors on my part). Thanks for your help.

For the rest I got:

3.
98L of CO2 --> 3.953mol
H2O/CO2 = 3/2 x 3.953mol
= 5.9295mol of water
= 106.82g
(where 1g=1mL) = 106.82mL

4.
8g of O2 = .25mol
H2S/O2 = 2/3 x .25
= 1/6mol of H2S x 22.71(MV)
= 3.785L

5.
107g of NH4Cl = ~2mol
NH3/NH4Cl = 2/2 x 2
= 2mol x 22.71(MV)
= 45.427L

 

[mitochondria]

All of them look right to me

 

[XcarvengerX]

My teacher is very strict and I would lose 1 mark if I don't write the correct significant figure. And I think this is also the case for HSC in past years.

For number 4 and 5, I think you should leave the answers at 2 decimal place as the least significant number in these questions is 1.00.

I might be wrong. I keep getting wrong about determining significant figure of some value, like 100.00 and 0.00100 - I thought both of them got the same number of significant figure. Correct me if that's incorrect.

 

[mitochondria]

Your teacher is right to fuss about sig. figs. There's no point to report something that is of little or no importance, right?

A few rules for sig. figs:

- Numbers such as 9999, 123, and 46 have siginificant figures equal to the number of digits. (i.e. 9999 has 4 sig. figs.; 123 has 3 sig. figs; and 46 has 2 sig. figs.)

- Zeros to the left of the decimal point are usually considered to be insignificant if there's nothing to the right of the decimal point. For example, 100 has 1 sig. fig. and 2200 has 2 sig. figs.

- The zeros to the right of the decimal point are considered insignificant if there it is only a zero (or are only zero <---- I'm not sure why anyone would do that and I've never seen it before; but weird things do happen) to the left of the decimal point. For example, 0.001 has 1 sig. fig.; 0.00000001 has 1 sig. fig.; and 0.00100 has 3 sig. figs.

- When there one or more zeros to the right of the decimal point, everything in front of or after the decimal point are considered significant. For example, 100.00 has 5 sig. figs.; 1000.0 has 5 sig. figs.; and 10.000 has 5 sig. figs.

I hope that answered your question!

The following is probably not of any significant value to you (at least not for the HSC), but it's handy to know that:
Reference: Mathematical Methods for Introductory Physics with Calculus 3e, Davidson, Saunders College Publishing, 1994.

2.682 +/- 0.002m
2.682 +/- 0.004m
2.6821 +/- 0.0016m
2.6821 +/- 0.0009m

all have the same shorthand value = 2.682m

More examples (take notice the round-offs):

7.687 +/- 0.012m ----> 7.69m
3.132 +/- 0.026m ----> 3.13m
8.274 +/- 0.010m ----> 8.27m

 

[XcarvengerX]

So how do you write 100 to 2 significant figures?

 

[Riviet]

1.0 x 10²

 

[jjames-hall]

i think a golden rule is not to round up till you have finished and write out hte full long decimal answer and then round up or got to ho wmany significant figures. At least then they can see you did all the calcualations right

 

[funking_you]

Hi,

I have provided worked solutions for questions very similiar to this, which you may want to have a go at as well for more practice:


http://community.boredofstudies.org...-questions-answered-assistance-resources.html

Go to MODULE 2 -----> "Acid/Base Theory Q&A"


Cheers,
George

 

[pLuvia]

Yes I agree. Now it's easy to store the repeating numbers in those new calculators

 

[Vaishali]

can ANY one plz tell me
HOW DO U DO THIS???
what is the actual formula and procedure????
i have my half yearly exam of chem on 5th april and i CANT get the calculation stuff correct!!! plz help
plzzzzzz

 

[pLuvia]

The formulae you will need are

n=m/M
c=n/V
MW_compound
n=V/V_a

At 0*C and 100.0kPa, the molar volume of all gases is 22.71 L
At 25*C and 100.0kPa, the molar volume of all gases is 24.79 L

But the last two are given in the periodic table sheet

Using the moles of the chemical equation

It's your ability to apply these formulae towards the question, each question varies in procedure, post a question up and members will help you through it

 

[passion89]

I'm a bit confused here...there's a question which I don't fully understand.

Include the calculation method of calculating how much CO2 is produced for the reaction of fermentation of sugar into ethanol.

My teacher said she only wants the formulas we would use...but what are they? She said there are two. Also she told me that it doesn't matter that there aren't any numbers or masses given that we can work with we just have to answer the question hypothetically.

Can anyone please help me? Thank you!

 

[Riviet]

C₆H₁₂O_6(aq) -> 2CH₃CH₂OH_(aq) + 2CO_2(g)

Using equation n=m/M, we can find the number of moles of glucose reacted, multiply it by 2, since mole ratio of CO₂ to glucose is 2:1. Depending on what you want to find, you may need to use the equation n=cV to find the volume of CO₂ produced from the reaction. I hope that helped.

 

[passion89]

Yeah I gave the questions in with the molarity and number of moles formulas and it was wrong :mad1: I blame the teacher for giving us such a stupidly worded question. Seriously who could figure that out without numbers and figures...?