[Sheryl Killen]

The following are ?'s that I need help with..
1) A)Calculate the % of Aluminum in Al2(SO4)3 & AL(NO3)3. B)Which has the largest % of Aluminum?

2)How many grams of Oxygen are present in 2.01 x 10 to the 22nd molecules of HNO3?

3)A hydrocarbon fuel consits of 84.09% carbon & 15.91% hydrogen. A) Calculate the empirical formula of this fuel. B)If the molar mass of this fuel is 114.26 grams per mole, What is the molecular formula of this compound?
 
4)In the following reaction (check if balanced) how many molecules of NO2 are produced if 5.00g of N2H4 reacted?  N2H4 + 3 O2 --> 2NO2 + 2H2O?

5)HNO3 decomposes according to the following balanced reaction given below.  Starting w/ 4.0 x 10 to the 24th molecules of HNO3, how many moles of water will be produced?  How many grams of H2O will be produced?  4HNO3 --> 4NO2 +2H2O +O2

6) Aspirin (C9H8O4)can be made in the laboratory by reacting salicylic acid (C7H6O3) with acetyl chloride(C2H3ClO)  C7H6O3 + C2H3ClO --> C9H8O4 + HCl, What mass of aspirin is produced by the complete reaction of 50.0 g of salicylic acid?

7)How many grams of PH3 are needed to produce 45.3 grams of H2O using the reaction 4PH3(gas) + 8O2(gas) --> P4O10(solid) + 6H2O(gas).

[jdurg]

I'd love to help you, but if I were to just give you the answers you really wouldn't learn anything and chemistry would only become exceptionally harder as you move along.  Show us what you have attempted with each of these questions and where you're getting stuck, and then we'll be able to help you along.  Trust me, it will be much more valuable to you if we proceed that way than if we just tell you the answers.  

[Donaldson Tan]

Hope this will help you understand mole concept in terms of working out the solutions to your posted question.

what is the percentage mass of water is oxygen atoms?

the formula of water is H-O-H. It consists of 2 H and 1 O atoms. This translates to 18g per mole for the molar mass of water. of the 18g, 16g is attributed to oxygen atom (because it contains 1 oxygen atom per molecule).

Hence the required percentage mass of water for oxygen atoms = 16/18 x 100% = 89%

[Sheryl Killen]

To Geodome, Glorified Plumber,
Are you referring to #5?? The following is how I came to my answer:  4.0 X 10 to the 24th molecules HNO3  X 1 mole HNO3/ 6.022 x 10 to the 23rd molecules HNO3 X 2 moles H2O/4 moles HNO3 =(ANSWER#5A) 3.3 moles H2O will be produced.     3.3 moles H2O/1 X 18.02 grams H2O/1mole H2O = (ANSWER#5B) 59 grams H2O will be produced.    

[Donaldson Tan]

 

it's actually a hint for question (2)

[Donaldson Tan]

question(5)

4HNO3 --> 4NO2 +2H2O +O2
The molar ratio of H2O to HNO3 is 2:4 = 1/2, ie. every 2 molecules of HNO3 give u 1 molecule of water.

mass of water formed
= number of water molecules formed x molecular weight of water
= (1/2 x number of HNO3 molecules reacted) x molecular weight of water

[Sheryl Killen]

not quite understanding the 2 replies that I have rcvd.  Re the hint for #2, we're not looking for percentage mass of water for oxygen atoms, we're looking for # of grams that are present in 2.01 X 10 to the 22nd molecules of HNO3. This is what I came up with:  2.01 X 10 to the 22nd HNO3 Molecules X 1 mole HNO3/6.022 x 10 to the 22n3rd molecules HNO3 X 3 moles O/1mole HNO3 X 16grams O = 1.60 grams O are present... Re #5 I worked out the problem and put my answer above.  Am I on the right track for these two problems? .2s.

[Donaldson Tan]

your answer for (5) is correct.

I was trying to tell you for (2) that the percentage mass composition of an element in a molecule corresponds to percentage mass composition of the same element in a big amount of the same substance if pure.

[Sheryl Killen]

Do I have #2 correct as well?? This is what I came up w/for #3): C= 96.08 grams C X 1 mole C/12.01 grams C = 8 moles Carbon = 8/8 = 1, & H = 18.18 grams H X 1 mole/H /1.01 grams H = 18 moles Hydrogen = 18/8 = 2.25        3A)Empirical Formula= CH2.25 & 3B)C4H9 Molecular Formula
#4)5.00g N2H4 X 1 mole N2H4/32.06 g N2H4 X 2NO2moles/1mole N2H4 X 6.022 x10 to the 23rd molecules NO2/1mole NO2= 1.88 X 10 23rd molecules NO2
 Am I on the right track for these ones as well??