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mazda215 mazda215
wrote...
13 years ago
now i know this is a biology forum but i got a post in the chem section of yahoo answers so i decided to come here....not sure if you guys will know the answers though  Sad Dummy.

Question 1.

Some household drain cleaners consist of a mixture of granules of sodium hydroxide and powdered aluminum. When dissolved in water, the sodium hydroxide reacts with the aluminum to produce hydrogen gas. The sodium hydroxide helps dissolve grease, and the hydrogen gas provides mixing and scrubbing action. What mass of hydrogen gas would be formed from a mixture of 2.48g Al and 4.76g NaOH?

the equation they gave with this question is :
2 Al (s) + 2 NaOH (s) + 6H2O (L) ---> 2NaAl(OH)4 + 3H2 (g)


Question 2.

Phosphorus sulfide P4S3 is used in the heads of wooden matches. This material is manufactured by hearing a mixture of red phosphorus P4 and sulfur S8. If 10.0 g of phosphorus and 17.0g of sulfur react, how much phosphorus will be produced?


can anyone show the steps to doing BOTH questions?? thanks to anyone who answers
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Replies
wrote...
#1
Educator
13 years ago
We are always open to helping.

For number (1), would a problem like this job you memory?

Mg + H(2)SO(4) -------> MgSO(4) + H(2)

Where we are being ask: What mass of hydrogen gas would be evolved if 6.075 g of magnesium reacted completely with dilute suphruric acid?

Convert the magnesium to moles:

6.075g x (1mol/24.31g) = 0.2499mols

the ratio of Mg to H2 is 1:1

so 0.2499 mols Mg = 0.2499mols H2

molar mass of H is 1.01, molar mass of H2 is 2(1.01) or 2.02

convert to mols:

0.2499 mols H2 x (2.02g/1mol) = 0.5 mass H2 gas

For Number 2

3S8 + 8P4 ---> 8P4S3

use the weight they gave you, i.e. 10 and 17.

S8 moles: 17g/(32.066) g/mol= Ans*8 = 0.0663 mols
P4 moles: 10g/(30.974) g/mol = Ans*4 = 0.0807 mols

when 0.0807 moles of P4 have reacted 3/8(0.0807) = 0.0303 moles S8 will have reacted. S8 in excess so P4 is limiting reagent. Moles P4= moles P4S3.

molar mass P4S3= 4(30.974)+3(32.066)=216.5g/mole

0.0807 moles 216.5 g/mole = 17.5 g P4S3
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