Skip to main content
Chemistry LibreTexts

3.11 Practice Problems

  • Page ID
    142215
  • Chemical Formulas

    1. For the following molecules; write the chemical formula, 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

    b) iron (II) chloride

    c) dinitrogen pentoxide

    d) iron (III) sulfate

    Exercise \(\PageIndex{1}\)

    Answers to Q1

    Answer
    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. Name 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

    Answer
    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

    Answer

    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 hybridization of the central atom(s), c) determine the EGA around the central atom(s), d) determine the MG around the central atom(s), e) determine the bond angles in the molecule, f) determine if the molecule is polar or non-polar

    Exercise \(\PageIndex{4}\)

    Answers to Lewis dot questions

    Answer

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

    ii) a) PI3.jpg b) sp3 c) tetrahedron d) trigonal pyramid e) <109.5o f) polar

    iii) a) SCl2.jpg b) sp3 c) tetrahedron d) bent e) <109.5o f) polar

    iv) a) CH2PH.jpg b) C sp2 and N sp2 c) C and N trigonal plane d) C trigonal plane; N bent e) <120o f) polar