Chemistry HL/SL help

[Rigel]

Hey guys i got another question:

Calculate the volumen of CO₂ produced when 1.00g of calcium carbonate reacts with 20.0cm³ of HCl. Assume the volume of the gas is measured at 273K and 1 atm.

In this one, i'm not so sure if you have to find the Limiting Reactant... Also, the only thing we are given about HCl is only the volume, and the concentration? Never done this kind of problem. Kinda worries me hehe. Answer: 224cm³. I actually got the final answer, but i'm not so sure about that part of the limiting reactant, and, why are we given the volume of HCl, is it even necessary to work with it?

Thanks!

[Alex1307]

Hey guys i got another question:

Calculate the volumen of CO₂ produced when 1.00g of calcium carbonate reacts with 20.0cm³ of HCl. Assume the volume of the gas is measured at 273K and 1 atm.

In this one, i'm not so sure if you have to find the Limiting Reactant... Also, the only thing we are given about HCl is only the volume, and the concentration? Never done this kind of problem. Kinda worries me hehe. Answer: 224cm³. I actually got the final answer, but i'm not so sure about that part of the limiting reactant, and, why are we given the volume of HCl, is it even necessary to work with it?

Thanks!

First you need to find the number of mol of each reagent! CaCO₃ is easy, as you just divide the mass by the molecular mass (1/100= 0.01 mol).

For the HCl, are you sure there is no concentration? because unless you're given the concentration you cannot use the formula:

nHCl = concentration * volume (in dm³)

Anyways, you also need to write down the equation, which should be something like:

CaCO₃ + 2HCl = CaCl₂ + CO₂ + H₂O

But if you don't have the concentration of HCl then I'm really stuck, I don't know how to solve this question...

[Drake Glau]

Hey guys i got another question:

Calculate the volumen of CO₂ produced when 1.00g of calcium carbonate reacts with 20.0cm³ of HCl. Assume the volume of the gas is measured at 273K and 1 atm.

In this one, i'm not so sure if you have to find the Limiting Reactant... Also, the only thing we are given about HCl is only the volume, and the concentration? Never done this kind of problem. Kinda worries me hehe. Answer: 224cm³. I actually got the final answer, but i'm not so sure about that part of the limiting reactant, and, why are we given the volume of HCl, is it even necessary to work with it?

Thanks!

I would assume the calcium carbonate as the limiting reactant because there is no way to find your moles of HCl from the information given...

After that it's just a simple find your moles of CaCarbonate and do a mol:mol ratio And then convert to your volume of course. I don't what number this method gives you though

I agree it seems weird that they give you the volume of HCl though, but nothing else...

[Rigel]

No hehe it's a bit weird honestly. This question is from the Pearson Bac. Chem Book, but i suppose that was a mistake.

Btw,

Can someone explain the diference between a continuous spectrum and a line spectrum?

Thanks Drake and Alex!

Actually my book says something weird about these:

n = (Concentration x Volume)/1000

[Alex1307]

Actually my book says something weird about these:

n = (Concentration x Volume)/1000

Because you were given the volume in cm³

You can only use this formula with dm³ and the easiest way to go from cm³ to dm³ is to divide by 1000

Edited May 17, 2011 by Alex1307

[Drake Glau]

c=n/v

n=cv

v=n/c

Learn those and you're good

Just make sure v is ALWAYS in liters.

Continuous spectrum are...continuous...i dont know how to explain it honestly. Think of a prism...the rainbow even, it's continuous. A line spectrum is the emission of individual wavelengths. Each elements when heated (or energy added to it, same thing) has a specific line spectrum where the e- can only change orbitals so much. This creates unique colors for each elements. Random tidbit: Transition metals get their colors from electrons changing D-orbitals (there's 5 of them in each energy level). It came up in p1 this year

[Alex1307]

No hehe it's a bit weird honestly. This question is from the Pearson Bac. Chem Book, but i suppose that was a mistake.

Btw,

Can someone explain the diference between a continuous spectrum and a line spectrum?

Continuous spectrum is the series of all the visible wavelengths of light (from violet to red or the other way round).

And line spectrum is the just some of the wavelengths. It can be emission spectrum (light emitted by a compound/element) or absorption spectrum (light absorbed by a compound/element). The emission and absorption spectrum are complementary!

Picture spectrum

[Alex1307]

Hey guys i got another question:

Calculate the volumen of CO₂ produced when 1.00g of calcium carbonate reacts with 20.0cm³ of HCl. Assume the volume of the gas is measured at 273K and 1 atm.

In this one, i'm not so sure if you have to find the Limiting Reactant... Also, the only thing we are given about HCl is only the volume, and the concentration? Never done this kind of problem. Kinda worries me hehe. Answer: 224cm³. I actually got the final answer, but i'm not so sure about that part of the limiting reactant, and, why are we given the volume of HCl, is it even necessary to work with it?

Thanks!

OH I FOUND THE ANSWER haha (finally)

So, as Drake Glau said, you do use CaCO3 as a limiting reagent. So nCaCO3 = 0.01 and according to the equation there should be 0.01 of CO2 as well.

Now you just use the formula:

PV = nRT

Which gives:

V=nRT/P

where n=0.01, R = 8.31, T = 273 and P = 101000 Pa (=1 atm)

So the V = (0.01 * 8.31 * 273)/101000 = 0.00224 m³

So now you just mutliply it by 1000 to find 0.224 dm³, and again by 1000 to find 224 cm³

Problem solved

Edited May 17, 2011 by Alex1307

[Rigel]

Hey guys i got another question:

Calculate the volumen of CO₂ produced when 1.00g of calcium carbonate reacts with 20.0cm³ of HCl. Assume the volume of the gas is measured at 273K and 1 atm.

In this one, i'm not so sure if you have to find the Limiting Reactant... Also, the only thing we are given about HCl is only the volume, and the concentration? Never done this kind of problem. Kinda worries me hehe. Answer: 224cm³. I actually got the final answer, but i'm not so sure about that part of the limiting reactant, and, why are we given the volume of HCl, is it even necessary to work with it?

Thanks!

OH I FOUND THE ANSWER haha (finally)

So, as Drake Glau said, you do use CaCO3 as a limiting reagent. So nCaCO3 = 0.01 and according to the equation there should be 0.01 of CO2 as well.

Now you just use the formula:

PV = nRT

Which gives:

V=nRT/P

where n=0.01, R = 8.31, T = 273 and P = 10100 Pa (=1 atm)

So the V = (0.01 * 8.31 * 273)/10100 = 0.00224 m³

So now you just mutliply it by 100000 to find 224 cm^3[/sup]!

^{Problem solved}

^{Thank you very much!}

^{So we just forget about the volume in the HCl right?}

^{Oh and another question,}

^{Could someone define the electromagnetic spectrum?}

[Alex1307]

Oh and another question,

Could someone define the electromagnetic spectrum?

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiations, such as radio, microwaves, infrared, visible light, ultraviolet, x-rays and so on!

It's a the bottom of the first page of your data booklet if you want to take a look at it!

Edited May 17, 2011 by Alex1307

[Drake Glau]

where n=0.01, R = 8.31, T = 273 and P = 101000 Pa (=1 atm)

So the V = (0.01 * 8.31 * 273)/101000 = 0.00224 m³

So now you just mutliply it by 1000 to find 0.224 dm³, and again by 1000 to find 224 cm³

I agree, except you're missing a zero in your cubic meters

you also don't need to go through the trouble of the ideal gas equation. 0.01mol of CO2=0.01*22.4L=0.224L or 224mL

Edited May 17, 2011 by Drake Glau

[Alex1307]

where n=0.01, R = 8.31, T = 273 and P = 101000 Pa (=1 atm)

So the V = (0.01 * 8.31 * 273)/101000 = 0.00224 m³

So now you just mutliply it by 1000 to find 0.224 dm³, and again by 1000 to find 224 cm³

I agree, except you're missing a zero in your cubic meters

you also don't need to go through the trouble of the ideal gas equation. 0.01mol of CO2=0.01*22.4L=0.224L or 224mL

REALLY?! Oh dear I've been going through two years of Chem HL with using this super complicated formula and its weird units... I totally forgot about the ideal gas constant...

Oh well, it's too late! No more chem (till uni starts!)

[Hinuku]

Hi, I have found this exersise online and I have no idea how to solve it

Consider the synthesis equilibrium reaction for ammonia:

N2(g) + 3 H2(g) ↔ 2 NH3 (g)

In a certain experiment, 1.000 mole of N2(g) and 1.000 mole of H2(g) were placed in a 1.000 dm3

flask at 500°C

and allowed to react. After the system reached equilibrium, the flask was found to contain 0.921 mole of N2.

Calculate the equilibrium concentrations of H2 and NH3 and calculate the Kc for this reaction at 500°C.

Thanks

[Drake Glau]

It's a bunch of ratios.

If 0.921mol of N2 is left then 0.079mol is reacting and the ratio of N2 to NH3 is 2:1 so that's 0.158mol of NH3. You need 3 H2 per mole of NH3 so you can then take the 0.158*3 and get 0.474mol of H2

It's a 1 liter flask so your moles are basically your concentration, no point in doing the mental math...

Kc, i'm sure you know how to do from here

[dessskris]

Does bond polarity have any effect on the bond length? Like if the bond is more polar, I think the attraction will be greater and so the bond will be shorter. Is it correct? Please note that I'm talking about the polarity of the bond and not the polarity of the molecule. Thanks.

[Keel]

Does bond polarity have any effect on the bond length? Like if the bond is more polar, I think the attraction will be greater and so the bond will be shorter. Is it correct? Please note that I'm talking about the polarity of the bond and not the polarity of the molecule. Thanks.

Yes, the more polar a bond is the larger the difference in electronegativity of the two elements thus the stronger the bond. As a rule of thumb, the stronger the bond the shorter the bond length. However, you must bear in mind that polarity is not the only factor which determines bond length. The more electrons involved in an electron density region, the shorter the bond will be (as seen with carbon double and triple bonds which are not polar).

[dessskris]

it makes sense. thank you!

now is anybody willing to explain to me about emission spectra? like when electrons are excited and then drop etc etc and the energy emitted, the wavelength and the colour of the spectrum? I don't really get it... I only know that the farther the electron drop is the more energy is emitted. more energy emitted means higher wavelength or lower? how does it affect the colour of the spectrum, does it follow ROYGBIV?

oh and I also know that electron drop from n 3 to n 2 emits less energy than that from n 2 to n 1 because of the distance and the emergence thingy...

my chem exam is tomorrow. thanks a lot!

Edited May 25, 2011 by dessskris

[Keel]

it makes sense. thank you!

now is anybody willing to explain to me about emission spectra? like when electrons are excited and then drop etc etc and the energy emitted, the wavelength and the colour of the spectrum? I don't really get it... I only know that the farther the electron drop is the more energy is emitted. more energy emitted means higher wavelength or lower? how does it affect the colour of the spectrum, does it follow ROYGBIV?

oh and I also know that electron drop from n 3 to n 2 emits less energy than that from n 2 to n 1 because of the distance and the emergence thingy...

my chem exam is tomorrow. thanks a lot!

The animation does it quite well (turn sound on). http://ibchem.com/IB/ibnotes/full/ato_htm/2.3.htm

[Drake Glau]

it makes sense. thank you!

now is anybody willing to explain to me about emission spectra? like when electrons are excited and then drop etc etc and the energy emitted, the wavelength and the colour of the spectrum? I don't really get it... I only know that the farther the electron drop is the more energy is emitted. more energy emitted means higher wavelength or lower? how does it affect the colour of the spectrum, does it follow ROYGBIV?

oh and I also know that electron drop from n 3 to n 2 emits less energy than that from n 2 to n 1 because of the distance and the emergence thingy...

my chem exam is tomorrow. thanks a lot!

You'll learn this in physics too sort of. The bigger the drops, the more energy, the higher the frequency and thus a shorter wavelengths. ROYGBIV is in order by increasing frequency too. You don't need to know a ton about this either. You need to know the 3 series for hydrogen (balmer, lychen or something and another, I don't remember the 3 ) and they're corresponding light "types" (balmer is infrared, the middle one is visible light and then next one up is UV)

You also need to know (p1 thing to remember) that transition metals give off diferent colors by their electrons changing D orbitals. D. D. D.

[Hinuku]

Why is there a sign of eqm (I guess that stands for equimolar) beside every concentration of the molecules? I'm talking about the topic equilibrium and it's in the equation for Kc. I just don't understand why should it be there and what does it mean in this case.

Thanks!!