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4.6 Practice Problems

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    Chemical Formulas

    1. For the following molecules, determine how many atoms are present in one molecule/formula unit, determine the molar mass, determine the number of moles in 1.00 gram, and the number of grams in exactly 5.00 x 10-2 moles.

    a) carbon dioxide, CO

    b) iron (II) chloride, FeCl2

    c) dinitrogen pentoxide, N2O5

    d) iron (III) sulfate, Fe2(SO4)3

    Exercise \(\PageIndex{1}\)

    Answers to Q1

    Formula Atoms per Molecule/Formula Unit Molar Mass Moles in 1.00 g Grams in 5.00 x 10-2 moles
    CO2 3 44.01 2.27 x 10-2 2.20
    FeCl2 3 126.75 7.89 x 10-3 6.34
    N2O5 7 108.02 9.26 x 10-3 5.40
    Fe2(SO4)3 17 399.88 2.50 x 10-3 20.0

    2. For the following compounds, determine the molar mass, determine how many O atoms are present in one molecule/formula unit, determine the grams of oxygen in 1.00 mole of the compound, and determine how many moles of O atoms in 8.35 grams of the compound.

    a) K2CO3

    b) Ca(NO3)2

    c) Cu2SO4

    d) N2O

    Exercise \(\PageIndex{2}\)

    Answers to Q2

    Name Molar mass Atoms O per Molecule/Formula Unit Grams of O in 1.00 mole Moles of O in 8.35 grams
    potassium carbonate 138.205 3 48.0 1.81 x 10-1
    calcium nitrate 164.088 6 96.0 3.05 x 10-1
    copper(I) sulfate 223.25 4 64.0 1.50 x 10-1
    dinitrogen monoxide 44.013 1 16.0 1.90 x 10-1

    3. Give the chemical formula (including the charge!) for the following ions. Also, write out the chemical formula for the compound each anion would form with K+ and with Ca2+.

    a) sulfate

    b) sulfite

    c) nitrate

    d) chloride

    e) nitride

    f) acetate

    g) carbonate

    Exercise \(\PageIndex{3}\)

    Answers to Q3


    a) SO42-; K2SO4; CaSO4

    b) SO32-; K2SO3; CaSO3

    c) NO3-; KNO3; Ca(NO3)2

    d) Cl-; KCl; CaCl2

    e) N3-; K3N; Ca3N2

    f) C2H3O2-; KC2H3O2; Ca(C2H3O2)2

    g) CO32-; K2CO3; CaCO3

    Lewis Dot Structures

    4. For the compounds i) SiS2, ii) PI3, iii) SCl2, and iv) CH2PH a) draw the Lewis dot structure, b) determine the EPA around the central atom(s), c) determine the MG around the central atom(s), d) determine the bond angles in the molecule, e) determine if the molecule is polar or non-polar

    Exercise \(\PageIndex{4}\)

    Answers to Lewis dot questions


    i) a) sis2.jpg b) line c) line d) 180o e) nonpolar

    ii) a) PI3.jpg b) tetrahedron c) trigonal pyramid d) <109.5o e) polar

    iii) a) SCl2.jpg b) tetrahedron c) bent d) <109.5o e) polar

    iv) a) CH2PH.jpg b) C and N trigonal plane c) C trigonal plane; N bent d) <120o e) polar


    Modified by Tom Neils (Grand Rapids Community College)  

    4.6 Practice Problems is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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