Dalton's Law of Definite proportions

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dalton's atomic model contained the idea that elements (kind of atoms) combine in simple whole number ratios to form compounds. The law of constant composition says that a compound is defined by a particular elemental atomic ratio which does not change. these atomic ratios can be studied by measuring the mass rations in chemical reacitons.

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13 Terms

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in compounds, elements combine in

  • whole number ratios

  • ratio does not change

  • ratio partially defines a compound

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ionic formula tells

ratio of elements

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molecular formula tells

  • ratio of elements

  • composition of molecule

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law of definite proportions

an empirical law that states elements will combine in specific, observable, mass ratios to form compounds

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formula of determining a percentage of an element in a compound

(Melement/Mcompound) x 100

<p>(M<sub>element</sub>/M<sub>compound</sub>) x 100</p><p></p>
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determine the percentage (by mass) of oxyegn in each of the oxides: FeO and Fe2O3

Iron (II) oxide: 22%
Iron (III) oxide: 30%

<p>Iron (II) oxide: 22%<br>Iron (III) oxide: 30%</p>
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formula of determining percentage of element produced based on mass

Mcompound/Melement = x/mass

<p>M<sub>compound</sub>/M<sub>element</sub> = x/mass</p>
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If 10.0g of Fe is reacted completely with oxygen, what mass of iron(x) oxide would be produced

MFeO/MFe = 72/56 = x/10.0
x = 72/56 × 10.0 g
x = 12.9 g
Fe2O3 = 14.3 g

<p>M<sub>FeO</sub>/M<sub>Fe </sub>= 72/56 = x/10.0 <br>x = 72/56 × 10.0 g <br>x = 12.9 g <br>Fe<sub>2</sub>O<sub>3</sub> = 14.3 g </p>
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percentage composition of a compound

what percentage of each element in a compound, calculate all then make sure they add up to 100%

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Find the percentage composition of ascorbic acid (C6H8O6)

C6H8O6

Molecular mass:

MC6H8Og = 6(12.011amu) + 8(1.00794amu) + 6(15.9994amu)

= 176.12592amu

%C = 6MCMC6H8O6 x 100%

= 6(12.011amu)176.12592amu x 100%

= 40.9%

%H = 8MHMC6H8O6 x 100%

= 8(1.00794amu)176.12592amu x 100%

= 4.57%

%O = 6MOMC6H8O6 x 100%

= 6(15.9994amu)176.12592amu x 100%

= 54.5%

Therefore ascorbic acid is 40.9% carbon, 4.57% hydrogen and 54.5% oxygen by mass.

<p>C6H8O6</p><p>Molecular mass: </p><p>MC6H8Og = 6(12.011amu) + 8(1.00794amu) + 6(15.9994amu)</p><p> = 176.12592amu</p><p>%C = 6MCMC6H8O6 x 100%</p><p> = 6(12.011amu)176.12592amu x 100%</p><p> = 40.9%</p><p>%H = 8MHMC6H8O6 x 100%</p><p> = 8(1.00794amu)176.12592amu x 100%</p><p> = 4.57%</p><p>%O = 6MOMC6H8O6 x 100%</p><p> = 6(15.9994amu)176.12592amu x 100%</p><p> = 54.5%</p><p>Therefore ascorbic acid is 40.9% carbon, 4.57% hydrogen and 54.5% oxygen by mass. </p><p></p>
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Determine the percentage composition of water in magnesium sulfate heptahydrate

MgSO4 · 7H2O

MMgSO4 · 7H2O = Mmg + Ms + 4Mo + 7MH2O

= (24.305amu) + 32.066amu + 4(15.9994amu) + 7(18.01528amu) = 246.47556amu

Molecular mass of water

= 2MH + MO = 2(1.00794amu) + 15.9994amu = 18.01528amu

% H2O = 7MH2O/MMgSO4 · 7H2O x 100% = 18.01528amu246.47556amu x 100% = 51.16%

<p>MgSO4 · 7H2O</p><p>MMgSO4 · 7H2O = M<sub>mg </sub>+ M<sub>s </sub>+ 4M<sub>o </sub>+ 7M<sub>H2O</sub></p><p>= (24.305amu) + 32.066amu + 4(15.9994amu) + 7(18.01528amu) = 246.47556amu</p><p>Molecular mass of water</p><p> = 2M<sub>H </sub>+ M<sub>O </sub>= 2(1.00794amu) + 15.9994amu = 18.01528amu</p><p>% H2O = 7M<sub>H2O/</sub>M<sub>MgSO4 · 7H2O </sub>x 100% = 18.01528amu246.47556amu x 100% = 51.16%</p>
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molecular mass

referring to mass of an entire molecule, ex. MH2O

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formula mass

referring to mass of an ionic compound, ex. MMgSO4