chemistry 1/2 questions thread

[spectroscopy]

yo guys, i needs tonnes of help for this stuff so ima get straight to it

in an experiment 20.00mL of hydrochloric acid was standardised by titration with a solution of 0.104M sodium carbonate 
the average titre of socium carbonate was 11.6ml
find the concentration of this solution of hydrochloric acid

[RKTR]

1st write the chemical equation

2HCl(aq) + Na2CO3(aq) --> 2NaCl(aq) + H2O(l)  + CO2(g)

from the equation,we can see that 2 mol of HCl reacts with 1 mol of Na2CO3
                                               ratio  2  :   1

find n of Na2CO3     n=cv    n=0.104 x ( 11.6/1000) = 1.21 x 10^-3 mol

n of HCl = 2 x n of Na2CO3  =  2(1.21 x 10^-3) mol
                                            =  2.42 x 10^-3 mol

n=cv   2.42 x 10^-3 = c ( 20.00/1000)
                     c=0.121 M
                       

[RazzMeTazz]

Hi, I know this is simple but can someone please explain to me how you would calculate the amount (in mol) of sodium atoms represented by 1.0 x 10^20 sodium atoms.

Thankyou! 

[brightsky]

1 mol of sodium atoms = 6.02 * 10^(23) sodium atoms. it follows that 1.0 * 10^(20) sodium atoms = (1.0 *10^(20))/(6.02 * 10^(23)) mol of sodium atoms. 

[RazzMeTazz]

1 mol of sodium atoms = 6.02 * 10^(23) sodium atoms. it follows that 1.0 * 10^(20) sodium atoms = (1.0 *10^(20))/(6.02 * 10^(23)) mol of sodium atoms.

Thankyou so much!

[RazzMeTazz]

Hi,
We are doing a prac sac in chemistry and our teacher said that we would be expected to know general theory about doing practical reports and answering questions about it

Has anyone does this type of thing in chemistry before?
What would it require us to know?
Just stuff like what the limitations are and what was the variable?

Thanks!

[alchemy]

Hi,
We are doing a prac sac in chemistry and our teacher said that we would be expected to know general theory about doing practical reports and answering questions about it

Has anyone does this type of thing in chemistry before?
What would it require us to know?
Just stuff like what the limitations are and what was the variable?

Thanks!

Have a look at this for an example, it might help: http://www.vcehelp.com.au/preparing-artificial-fragrances-and-flavours-vce-chemistry-prac-report-1691/
I've been told that criteria for Prac reports vary from school to school. So it's best if you ask your teacher for more details regarding this.

[RazzMeTazz]

Hi, I was wondering what did Rutherford's model of the atom say about electrons?
Did he propose that they were moving in random circular orbits around the nucleus?
Did he say that electrons belonged to random circular orbits?

Thanks!

[bucklr]

Hi, I was wondering what did Rutherford's model of the atom say about electrons?
Did he propose that they were moving in random circular orbits around the nucleus?
Did he say that electrons belonged to random circular orbits?

Thanks!

Your  right. His model disproved J.J Thompson's plumb pudding model where electrons where arranged in non-random rings.

Rutherford's model says that electrons move randomly, and that the an atom's mass is concentrated in the centre of the atom - the nucleus. Electrons were suggested by him to move randomly in rings of different energy levels.

[RazzMeTazz]

Your  right. His model disproved J.J Thompson's plumb pudding model where electrons where arranged in non-random rings.

Rutherford's model says that electrons move randomly, and that the an atom's mass is concentrated in the centre of the atom - the nucleus. Electrons where suggested by him to move randomly in rings of different energy levels.

Thankyou so much! 

[MNM101]

Hi I'm stuck on a chem unit 1 and 2 question also. We were learning about shells and there subs he'll and within the sub jells contains s,p,d,f but I'm really confused about all this plus the orbitals so if anyone can help me out that'd be great

[grannysmith]

Hi I'm stuck on a chem unit 1 and 2 question also. We were learning about shells and there subs he'll and within the sub jells contains s,p,d,f but I'm really confused about all this plus the orbitals so if anyone can help me out that'd be great

Schrodinger's model says that there are different energy levels (shells if you like) in which electrons can occupy. Whereas Bohr's model says that electrons of the same shell are of equal energy levels, Schrodinger's states that within these shells exist subshells. Electrons of different sub shells have varying energy levels, and these are termed s, p, d and f.
The s sub shell contains 1 orbital; p contains 3; d contains 5 and f contains 7.
An orbital can only hold a maximum of 2 electrons. Thus, the s sub shell has a maximum of 2 electrons; p has a max of 6 etc..
When electrons are given enough energy (e.g. heat), they can jump to higher energy levels (they can go from, say, 1s to 2p). However, electrons always want to be at their lowest energy state, their 'ground state'. That is, as close to the nucleus as possible. When they go from a higher energy level to a lower energy level, the energy must be emitted somehow. Usually, this is given of as a photon, which is essentially a packet of light.

Guys, correct me if I'm wrong. I've only learnt this ever so recently :p

[RazzMeTazz]

Hey,

Why does the core charge of an atom increase across a period, and stay the same as you go down a group?

THanks

[alchemy]

Hey,

Why does the core charge of an atom increase across a period, and stay the same as you go down a group?

Thanks

Yes. The core charge is basically the number of valence electrons, meaning they increase as you go across a period, and stay the same as you go down a group.

[RazzMeTazz]

I know if something is reduced, it has gained electrons but what does a reducing agent do?
Does it cause other substances to gain electrons? Or does it gain electrons itself?

thanks!