Q.1. How many molecules are present in

(a) 9 grams of water

(b) 17 grams of amonia

Q.2. Calculate the number of moles in 17 grams of H2O2

Q.3. Show that 12 grams of carbon-12 contains 6.023 x 1023 atoms of 12C

Q.4. What is the mass of one atom of hydrogen ?

Q.5. How many moles of Mg atoms are there in 100 grams of magnesium ?

Q.6. Neon gas consist of single atoms. What mass of neon contains 6.023 x 1023 atoms ?

Due to paucity of time it would not be possible for us to provide the answers to all your queries. We are providing solutions to some your good queries. Try solving rest of the questions yourself and if you face any difficulty then do get back to us.

1) No. of molecules in 9g of water:

Molecular mass of water(H2O)= (1×2)+16=18g/mol

1 mole of water=18g of water contains=6.022×1023 molecules of water

then 9g of water will have= (6.022×1023/18)×9 = 3.011×1023 molecules

2) No. of moles in 17g of H2O2:

no. of moles= mass / molecular mass

Molecular mass of  H2O2= (1×2)+(16×2)=34g/mole

so no. of moles of  H2O2 in 17g= 17/34=0.5

4)Mass of one atom of hydrogen:

1 mole i.e. 6.022×1023 atoms of hydrogen= 1g

then mass of one atom of hydrogen= 1/(6.022×1023)=1.6×10-24 g

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