When we use this formula no.of moles =given of particles/Avogadro no. Also give me one ex. of this. When we use this formula no.of moles= given mass/molar mass* Avogadro no. Also give me one ex. of this. How i can know what formula is applicable in the exam?????? tell me this clearly becoz exams are coming near and near?and this thing is not clear to me...

Asked by  | 5th Dec, 2012, 12:50: PM

Expert Answer:

Here is a graphic of the procedure steps:

1. no.of moles =given no of particles/Avogadro no.

Problem #1: 0.200 mole of H2O contains how many molecules?

Solution:   no.of moles =given no of particles/Avogadro no.

given no of particles =  no.of moles x Avogadro no.

0.200 mol x 6.022 x 1023 mol¯1

2. moles = mass ÷ molar mass

Calculate the moles in 124.5 g of oxygen gas.

  1. Write the equation: 
    n = m ÷ M

     

  2. Extract the data from the question: 
    m = 124.5 g

     

  3. Calculate the molar mass of the substance using the periodic table: 
    M(O2) = 2 x 16.00 =32.00 g mol-1

     

  4. Substitute the values into the equation and solve: 
    n = 124.5 ÷ 32.00 = 3.89 mol

Answered by  | 5th Dec, 2012, 01:58: PM

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