Chemistry HL/SL help

[Drake Glau]

god? no...but it's my best subject by far. Maybe only biology being better simply because it's "easier" content...

And idk about the book. Who's it by?

[Rigel]

god? no...but it's my best subject by far. Maybe only biology being better simply because it's "easier" content...

And idk about the book. Who's it by?

By G. Nauss. It's the one that has something that look like buckets of paint. I don't know. Hehe. I should be studying Spanish now.. TTYL

[saunders is god]

Does anyone know the equation for the formation of soap scum due to hard water?

[Drake Glau]

2C₁₇H₃₅COO^- + Ca²⁺ → (C₁₇H₃₅COO)₂Ca

http://en.wikipedia.org/wiki/Hard_water

Edited April 30, 2011 by Drake Glau

[IBavictim]

Hi, I just realized that my teacher completely missed "3.3 Chemical Properties" from the syllabus. Can someone help me on how I should answer:

3.3.1 Discuss the similarities and differences in the chemical properties of elements in the same group

3.3.2 Discuss the changes in nature, from ionic to covalent and from basic to acidic, of the oxides across period 3.

I do have an idea of what to say. However, my friend (an IB graduate) said that sometimes the IB examiners want very specific/exact answers, so I'm scared of missing out on important details.

Thanks in advance!

P.S. Goodluck to all the Chem HL and SL kids! I hope we all do well on these exams!

[Drake Glau]

Hi, I just realized that my teacher completely missed "3.3 Chemical Properties" from the syllabus. Can someone help me on how I should answer:

3.3.1 Discuss the similarities and differences in the chemical properties of elements in the same group

Elements in the same group will contain the same number of valence electrons and therefore tend to be similar in their chemical properties. That's really about it. Each element in that group will have a different number of shells also and I forgot what this does really...

3.3.2 Discuss the changes in nature, from ionic to covalent and from basic to acidic, of the oxides across period 3.

Just remember that ionic is a metal+nonmetal and covalent is two nonmetals. First element in period 3 is Na (metal) oxide means oxygen (nonmetal) therefore you get an ionic bond. Same with Mg and Al

Covalent bonds start happening when you move to the other side where the nonmetal are now binding with the oxygen from the "oxide" so you get a nonmetal+nonmetal which will yield you a covalent bond.

As for acid to bases your left side of period 3 form basic oxides, Aluminum oxide is amphoteric (meaning it can act as a base or acid depending on the conditions present) and your right side will form acidic oxides

I do have an idea of what to say. However, my friend (an IB graduate) said that sometimes the IB examiners want very specific/exact answers, so I'm scared of missing out on important details.

Yes, paper 1 likes these questions a lot

Thanks in advance!

P.S. Goodluck to all the Chem HL and SL kids! I hope we all do well on these exams!

Edited May 7, 2011 by Drake Glau

[IBavictim]

Thanks for your help!

I have another question that I'm not so sure how to answer:

4.5.1 Compare and explain the properties of substances resulting from different types of bonding.

[Teacher's Notes: Examples should include melting and boiling points, volatility, electrical conductivity and solubility in non-polar and polar solvents]

I'm having a great deal of trouble including all of those terms in my answer and a clear explanation. =\

Thanks again! As you can see, I have the most trouble with Bonding My apologies for asking too much. I know I'll learn to like it once I understand everything though

[Drake Glau]

Thanks for your help!

I have another question that I'm not so sure how to answer:

4.5.1 Compare and explain the properties of substances resulting from different types of bonding.

[Teacher's Notes: Examples should include melting and boiling points, volatility, electrical conductivity and solubility in non-polar and polar solvents]

I'm having a great deal of trouble including all of those terms in my answer and a clear explanation. =\

Thanks again! As you can see, I have the most trouble with Bonding My apologies for asking too much. I know I'll learn to like it once I understand everything though

Ionic - High melting point and boiling points, low volatility, conduct electricity when molten, soluble in polar solvents.

Covalent - Lower melting and boiling points than ionic, higher volatility that ionic, don't conduct electricity, soluble in non-polar (I think)

Metallic - Lower melting points that the other two above, conduct electricity due to the delocalized electrons involved with metallic bonding, not really soluble...try dissolving a metal someday

Dative (do you need to know dative? HL does =/) - I don't know what all you need know, at SL I'd assume you need to know that this is when both electrons of an electron pair are being transfered to form a bond instead of 1.

[Alex1307]

Thanks for your help!

4.5.1 Compare and explain the properties of substances resulting from different types of bonding.

[Teacher's Notes: Examples should include melting and boiling points, volatility, electrical conductivity and solubility in non-polar and polar solvents]

Boiling point and melting point depend on the strength of the intermolecular bonding (or forces). Metallic bonding is the strongest, so the boiling will be very high. The hydrogen bond (for example in water) will give a high boiling point. Very weak Van der Waals forces will result in low boiling point.

Electrical conductivity depends on the movement of electrons. Metallic bonding consist in delocalized electrons forming a "sea" of free electrons, allowing current to be conducted. Ionic structure (for example NaCl) can also conduct electricity but only when molten, as the electron are free to move in the liquid.

Polar solvent are most of the time made of compounds with hydrogen bonds and dipole-dipole forces (for example Chloromethane CH3Cl). Polar compound can easily mix with polar solvent.

Non polar solvent only have very weak Van der Waals forces (for example propane C3H8). They do not mix with polar solvent and often form a layer on top of the polar solvent. They do mix with other non polar solvent, with the same intermolecular forces.

The volatility is the tendency for a substance to vaporize. Once again, weak Van der Waals forces will lead to high volatility, as the particles are NOT attracted together very closely and some of them tend to "escape" (for example in octane C8H10). The weakest the bonding, the highest the volatility.

[iber2011]

Can someone please help me with this question?

What is the pH of the resulting solution when 20.cm3 of 0.20 M HCL is added to 100.00cm3 of 0.10M NH3? The pKb of NH3 is 4.75

[dessskris]

I think I am mixing things up... In an alkali, for example methylamine, it has one methyl group donating electrons to the N, neutralising its positive charge in the conjugate acid. It means the cation is more stable right? So does the methyl group make methylamine a weaker base or a stronger base (compared to ammonia)? If the conjugate acid is more stable does it mean that it is a weaker acid or a stronger acid and why?

This is further organic chem btw

[dessskris]

Can someone please help me with this question?

What is the pH of the resulting solution when 20.cm3 of 0.20 M HCL is added to 100.00cm3 of 0.10M NH3? The pKb of NH3 is 4.75

HCl + NH₃ --> NH₄Cl

n=conc/v

n(HCl)=0.20/0.020=10 mol

n(NH₃)=0.10/0.100=1 mol

(Did you type things correctly? Maybe the volume of HCl is 200 ml?)

Anyway, NH₃ is the limiting reagent.

n(NH₄Cl)=n(NH₃)=1 mol

Then you calculate the pH... Not sure how. Is this HL stuff?

[iber2011]

yes but it's ok i found out how to do it...thanks anyways

[Drake Glau]

n=conc/v

c=n/v

n=cv

[dessskris]

n=conc/v

c=n/v

n=cv

meh sorry! my brain wasn't really working yesterday... any help regarding question in post #151?

[Drake Glau]

Here's my BS, all i got =/

More stable in my head means it would be harder to dissociate which would make it weaker. As far as organic acids and what you're doing, I have no idea. We don't go deep into "organic acids", we just go into weak acids in general and organic is always special =/

[Rigel]

Need help on this exercise:

What is the maximum volume of CO₂ (Ideal conditions), that can be formed when 25.0cm³ of 0.800moldm^-3 HNO₃(aq) is added to 1.22g of Na₂CO₃(s)?

[Drake Glau]

2HNO₃+Na₂CO₃->2NaNO₃+CO₂+H₂O

First you need to convert everything to moles to determine the limiting reactant.

For a solution, n=cv (v must be in L or dm³)

n=0.800(0.025)=0.0200mol of HNO₃

1.22g/molar mass of Na₂CO₃

1.22g/105.99 (I got this from wikipedia because it's too early for me to actually find it myself...lazy )

0.0115mol of Na₂CO₃

This means Na₂CO₃ is the limiting reactant and therefore that amount of moles should be used during calculations.

Now it's just a 1:1 ratio so you form 0.0115mol of CO₂

Now according to avagadro's law (sort of, I think ), at ideal conditions a single mole of gas takes up 22.4dm³

0.0115*22.4=0.256dm³ or 0.256L or 256mL or 256cm³

Don't you need first to balance the equation?

The actual answer is: 448cm³

Even balancing I'm still getting the same answer, the limiting reactant is still the sodium carbonate and that's still 1:1 ratio with CO₂ O.o

The answer you have is taking the moles of HNO₃ and multiplying it by 22.4 which gives you 448mL but I don't understand how especially since that's a 1:2 ratio even if it were the limiting reactant...

Edited May 11, 2011 by Drake Glau

[Rigel]

HNO₃+Na₂CO₃->NaNO₃+CO₂+H₂O

First you need to convert everything to moles to determine the limiting reactant.

For a solution, n=cv (v must be in L or dm³)

n=0.800(0.025)=0.0200mol of HNO₃

1.22g/molar mass of Na₂CO₃

1.22g/105.99 (I got this from wikipedia because it's too early for me to actually find it myself...lazy )

0.0115mol of Na₂CO₃

This means Na₂CO₃ is the limiting reactant and therefore that amount of moles should be used during calculations.

Now it's just a 1:1 ratio so you form 0.0115mol of CO₂

Now according to avagadro's law (sort of, I think ), at ideal conditions a single mole of gas takes up 22.4dm³

0.0115*22.4=0.256dm³ or 0.256L or 256mL or 256cm³

Don't you need first to balance the equation?

The actual answer is: 448cm³

Edited May 10, 2011 by Ipos Manger

[nametaken]

HNO₃+Na₂CO₃->NaNO₃+CO₂+H₂O

First you need to convert everything to moles to determine the limiting reactant.

For a solution, n=cv (v must be in L or dm³)

n=0.800(0.025)=0.0200mol of HNO₃

1.22g/molar mass of Na₂CO₃

1.22g/105.99 (I got this from wikipedia because it's too early for me to actually find it myself...lazy )

0.0115mol of Na₂CO₃

This means Na₂CO₃ is the limiting reactant and therefore that amount of moles should be used during calculations.

Now it's just a 1:1 ratio so you form 0.0115mol of CO₂

Now according to avagadro's law (sort of, I think ), at ideal conditions a single mole of gas takes up 22.4dm³

0.0115*22.4=0.256dm³ or 0.256L or 256mL or 256cm³

Don't you need first to balance the equation?

Yes, I think you would balance the equation first.