67. What is the percentage of aluminum in aluminum oxide (Al2O3)?

A. 47%

B. 48%

C. 53%

D. 54%

68. What is the weight of 2moles of carbon dioxide?

A. 22.0 grams

B. 44.0 grams

C. 66.0 grams

D. 88.0 grams

4 Answers

  • Molar mass = 102 g/mol

    % Al = 2 x 27 x 100 / 102 = 53

    Molar mass CO2 = 44 g/mol

    2 mol x 44 g/mol = 88.0 g

  • molar mass of Al2O3 = 2*27+3*16= 54+48=102

    the weight fraction AL is 54/102= 52.94% so answer C

    1 mole of CO2 weighs 12+2*16 =44g

    so 2 moles 2*44=88g

    Answer D

  • add the masses of the 2 Al = numerator

    add the masses of the 2 Al and the 3 O = denominator

    multiply by 100 = the answer as a percent

  • molar mass of Al2O3=102g/mol

    %Al=(54/102)*100

    %Al=53%

    Ans;C

    n=m/M

    m=nM

    m=2*44

    m=88g

    Ans=D

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