How to calculate molecular formula

[BH20]

thanks..got it.

Few more easier ones but to make sure its right.

rounding to 3 significant figures...
i) 3.1747=3.17
ii) 0.0024652=0.00247
iii) 101.5=102
iv) 1.3463=1.35
v) 7.0021=7.0021

??

and another question asks if using a more expensive balance mattered in meausuring a mass of a sample..with the more expensive one, the mass was 75.357...using the less expensive it was 75.4...how do they differ? does it matter?

 

[BH20]

and just to check an answer...

if you are trying to find ATOMS..and it gives you a mass of 52.5g of calcium metal, and we know the molarmass is 40.1gm/mol, we can find the moles..and then we times that by 6.02*10tothe23? what do you get as the answer? second time I did it, got a different answer than first time, so just wondering.

 

[Gokul43201]

thanks..got it.

Few more easier ones but to make sure its right.

rounding to 3 significant figures...
i) 3.1747=3.17
ii) 0.0024652=0.00247
iii) 101.5=102
iv) 1.3463=1.35
v) 7.0021=7.0021

??

and another question asks if using a more expensive balance mattered in meausuring a mass of a sample..with the more expensive one, the mass was 75.357...using the less expensive it was 75.4...how do they differ? does it matter?

v) 7.0021 ~ 7.00 (to 3 sig. figs)

The balance question : This depends on other data in the problem. If you are given other numbers to only 2 or 3 sig figs, it doesn't help to buy the expensive balance because the error will be dominated by the accuracy of those numbers, not by the balance. If all other numbers are quoted to 5 sig figs or better, then the hot-shot balance would be handy.

The ATOMS question : (doing this in my head) The answer should be a little less than 8*10^23. The method you described is correct.

 

[BH20]

v) 7.0021 ~ 7.00 (to 3 sig. figs)

The balance question : This depends on other data in the problem. If you are given other numbers to only 2 or 3 sig figs, it doesn't help to buy the expensive balance because the error will be dominated by the accuracy of those numbers, not by the balance. If all other numbers are quoted to 5 sig figs or better, then the hot-shot balance would be handy.

The ATOMS question : (doing this in my head) The answer should be a little less than 8*10^23. The method you described is correct.

I got, 7.826 * 10tothe24? sound about right?

and the other question..(the balances) its in reagards to how much heat was lost or gained. Q=c*m*T...it says that in the example, and likley key part, "for both meauseraments, the last digit is uncertain"..so that woud likley mean it would not matter which one is used?

 

[Gokul43201]

Depends on how many sig figs before that "last digit"...

 

[BH20]

Depends on how many sig figs before that "last digit"...

ah ok..got it.

 

[BH20]

they have this in the book...

2.0g divided by 71.0g/mol * 6.02 *10tothe23

somehow when I calculate the EXACT same thing, I get 1.7*10tothe23..they get to the 22.

any idea?

 

[BH20]

they have this in the book...

2.0g divided by 71.0g/mol * 6.02 *10tothe23

somehow when I calculate the EXACT same thing, I get 1.7*10tothe23..they get to the 22.

any idea why?

 

[Gokul43201]

1.7 * 10^22 is correct. You must be making a mistake. Multiply numerators, 6*2=12
Now 12/71 =0.17. So, it 0.17*10^23 = 1.7*10^22

 

[BH20]

hmm..still don't get that..weird.

what would the correct formula for Manganese(II) iodite be?

 

[Gokul43201]

Mn(IO_2)2

Go to Ch. 4 : http://www.egusd.k12.ca.us/elkgrovehigh/Summer/APchemSUMMERWORK.htm

 

[BH20]

Some more questions:

1. What were the limitations of Dalton's atomic theory?

2. What do you get when you calculate 1.30mol * 6.02*10tothe23...since I keep getting the wrong answer when I type in the books example, want to see if I'm getting this wrong too.

 

[Gokul43201]

1. try googling
2. about 7.8*10^23

 

[BH20]

hmm, yeah, tried that right of the bat, I can find obviously the main points about the theory, but can't find the limitations anywhere.

 

[FZ+]

http://dl.clackamas.cc.or.us/ch104-04/dalton's.htm

Reading from this, a number of limitations leap to mind.

1. He characterises elements as atoms with the same mass. We now know that mass isn't important, chemistry wise. What is important is the electron configuration. An element is defined by proton number, not mass number.

2. Atoms are not indivisible, and indestructible, as we now know.

3. Compounds are not defined by the ratio of elements, but by their relationship to each other. Molecular formula, as opposed to empirical formula.