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A radioactive element has a half life of 200 days. The percentage of original activity remaining after 83 days is___________. (Nearest integer)

(Given : antilog 0.125 = 1.333, antilog 0.693 = 4.93)

0 3 Views | Posted 2 months ago
Asked by Shiksha User

  • 1 Answer

  • A

    Answered by

    alok kumar singh | Contributor-Level 10

    2 months ago

    t 1 / 2 = 2 0 0     d a y s = 0 . 6 9 3 k

    t = 2 . 3 0 3 k l o g 1 0 N 0 N

    83 =  2 . 3 0 3 0 . 6 9 3 × 2 0 0 l o g N 0 N

    8 3 = 2 0 0 0 . 3 0 1 0 l o g N 0 N

    0.125 = l o g N 0 N

    N 0 N = a n t i l o g ( 0 . 1 2 5 )

    = 1.333

    Activating remaining = N N 0 × 1 0 0

    = N 0 1 . 3 3 3 N 0 × 1 0 0

    = 75%

     

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A 0.5 percent solution of potassium choride was found to freeze at -0.24°C. The percentage dissociation of potassium chloride is__________. (Nearest integer)

(Molal depression constant for water is 1.80 K kg mol-1 and molar mass of KCl is 74.6 g mol-1)
A
alok kumar singh

0.5 % KCl solution has molality (m) = 0 . 5 × 1 0 0 0 7 4 . 5 × 9 9 . 5  

K C l ( a q ) ? K ( a g ) + + C l ( a q ) −  

1 - a        a          a

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i = Δ T f k f × m = 0 . 2 4 × 7 4 . 5 × 9 9 . 5 1 . 8 × 0 . 5 × 1 0 0 0 = 1 + α  

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% = 97.6%

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When 9.45g of ClCH2COOH is added to 500ml. of water, its freezing point drops by 0.5°C. The dissociation constant of ClCH2 COOH is x × 10-3. The value of x is__________ (Rounded off to the nearest integer)

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alok kumar singh

Δ T f = 0 . 5 ° C

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 a =   1 . 3 4 4 − 1 2 − 1 = 0 . 3 4 4

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           So; x = 36

          

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Kindly consider the following Image 

 

When 12.2g of benzoic acid is dissolved in 100g of water, the freezing point of solution was found to be -0.93°C [ K f ( H 2 O = 1 . 8 6 K   k g   m o l − 1 ] .  The number (n) of benzoic acid molecules associated (assuming 100% association) is…………,
V
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1.22 g of an organic acid is separately dissolved in 100 g of benzene (Kb = 2.6 K kg mol-1) and 100 g of acetone (Kb = 1.7 K kg mol-1). The acid is known to dimerize in benzene but remain as a monomer in acetone. The boiling point of the solution in acetone increases by 0.17°C. The increase in boiling point of solution in benzene in °C is x × 0-2. The value of x is ________. (Nearest integer)

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  Δ T b = i K b m

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0 . 1 7 = 1 × 1 . 7 × 1 . 2 2 × 1 0 0 0 M × 1 0 0

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2 A c i d → ( A c i d ) 2 ∴ i = 1 / 2

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= 1 2 × 2 . 6 × 1 . 2 2 × 1 0 0 0 1 2 2 × 1 0 0 ° C

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∴ x × 1 0 − 2 = 1 3 × 1 0 − 2

∴ x = 1 3

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