Abby 發問於 科學及數學化學 · 9 年 前

molar mass

A certain sample of calcium carbonate(CaCO3) contains 4.86mol.

a) What is the mass in grams of this sample?

b) What is the mass of the CO3^2- ions present?

PLEASE show your steps

更新:

仲有1條:

calculate the mass of magnesium oxide (MgO) formed when 2.43g of maganesium (Mg) are burnt with

a) excess ocygen

b)1.28g of oxygen

請教我點做, 唔好只比答案, 謝謝

更新 2:

第3條:

A mixture containing 2.8g of iron and 2g sulphur is heated together.

What is the mass of iron(II) sulphide, FeS, is produced?

Fe(s) + S(s) -->FeS(s)

我想知咩情況下先要搵limiting agent? 好似第3條咁係 1:1

咁係唔係選最細果個乘返FeS的atomic mass 等於the mass of FeS ?

ans 係咪. 4.4048g?

1 個解答

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  • 9 年 前
    最佳解答

    1.

    A certain sample of calcium carbonate(CaCO3) contains 4.86 mol.

    a) What is the mass in grams of this sample?

    b) What is the mass of the CO3²⁻ ions present?

    a)

    Molar mass of CaCO3 = 40 + 12 + 16x3 = 100 g/mol

    Mass of CaCO3­ = (4.86 mol) x (100 g/mol) = 486 g

    b)

    No. of moles of CO3²⁻ ions = No. of moles of CaCO3 = 4.86 mol

    Molar mass of CO3²⁻ ions = 12 + 16x3 = 60 g/mol

    Molar mass of CO3²⁻ ions = (4.86 mol) x (60 g/mol) = 291.6 g

    = = = = =

    2.

    calculate the mass of magnesium oxide (MgO) formed when 2.43g of maganesium (Mg) are burnt with

    a) excess oxygen

    b)1.28g of oxygen

    a)

    Molar mass of Mg = 24.3 g/mol

    Molar mass of O2 = 16x2 = 32 g/mol

    Molar mass of MgO = 24.3 + 16 = 40.3 g/mol

    2Mg + O2 → 2MgO

    Molar Mass Mg : MgO = 2 : 2 = 1 : 1

    No. of moles of Mg = (2.43 g) / (24.3 g/mol) = 0.1 mol

    No. of moles of MgO formed = 0.1 mol

    Mass of MgO formed = (0.1 mol) x (40.3 g/mol) = 4.03 g

    b)

    2Mg + O2 → 2MgO

    Molar Mass Mg : O2 : MgO = 2 : 1 : 2

    No. of moles of Mg present = 0.1 mol

    No. of moles of O2 present = (1.28 g)/ (32 g/mol) = 0.04 mol

    To complete react with 0.04 mol of O2,

    no. of moles of Mg needed = (0.04 mol) x 2 = 0.08 mol

    Hence, Mg is in excess, and O2 completely reacts (limiting reagent).

    No. of moles of O2 reacted = 0.04 mol

    No. of moles of MgO formed =- (0.04 mol) x 2 = 0.08 mol

    Mass of MgO formed = (0.08 mol) x (40.3 g/mol) = 3.224 g

    = = = = =

    3.

    A mixture containing 2.8 g of iron and 2 g sulphur is heated together. What is the mass of iron(II) sulphide, FeS, is produced?

    Fe(s) + S(s) → FeS(s)

    Molar mass of Fe = 55.8 g/mol

    Molar mass of S = 32.1 g/mol

    Molar mass of FeS = 55.8 + 32.1 = 87.9 g/mol

    Mole ratio Fe : S : FeS = 1 : 1 : 1

    No. of moles of Fe present = 2.8/55.8 = 0.0502 mol

    No. of moles of S present = 2/32.1 = 0.0623 mol

    Hence, Fe is the limiting reagent (completely reacted).

    No. of moles of Fe reacted = 0.0502 mol

    No. of moles of FeS formed = 0.0502 mol

    Mass of FeS formed = 0.0502 x 87.9 = 4.41 g

    資料來源: micatkie
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