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2015-06-18T21:52:12+05:30

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To determine the number of moles, find the molar mass of the substance and divide the given mass by the molar mass.

a. given mass, m = 3.43g
molar mass of carbon, M = 12g
Number of moles, n = 3.43/12 = 0.2858 moles

b. given mass, m = 7.05 g
molar mass of Br₂, M = 139.8g
Number of moles, n = 7.05/139.8 = 0.0504 moles

c. given mass, m = 76g
molar mass of C₄H₁₀, M = 58g
Number of moles, n = 76/58 = 1.3103 moles

d. given mass, m = 35.4g
molar mass of  Li₂CO₃ = 74g
Number of moles, n = 35.4/74 = 0.4784 moles
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2015-06-19T11:24:14+05:30

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One mole of a substance = Gram Molecular Weight of that substance(GMW)

a. 1 mole of Carbon = GMW of Carbon = 12g
    12g of carbon makes 1 mole
    3.43g of carbon makes how many moles? 
    = 1 × 3.43 / 12
    = 0.2858 moles ≈ 0.29 moles ≈ 0.3 moles

b. 1 mole of Br₂ = 160g (Br + Br = 80g + 80g)
    160g of Br₂ makes 1 mole
    7.05g of Br₂ makes how many moles?
    = 7.05 × 1 / 160
    = 0.044 moles ≈ 0.4 moles

c. 1 mole of C₄H₁₀ = 4(12) + 1(10) = 58g
    58g of C₄H₁₀ makes 1 mole
    76g of C₄H₁₀ makes how many moles?
    = 76 × 1 / 58
    = 1.310 moles ≈ 1.3 moles

d.1 mole of Li₂CO₃ = 2(7) + 12 + 3(48) = 74g
   74g of Li₂CO₃ makes 1 mole
   35.4g of Li₂CO₃ makes how many moles?
   = 35.4 × 1 / 74
   = 0.478 moles ≈ 0.48 moles ≈ 0.5 moles
   
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