Streptomyces:Other Bits/Useful Molecular and Chemical Equations: Difference between revisions
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The difference between formula weight and molecular weight depends on the compound. It is correct to refer to a compound such as Benzene having a molecular weight or formula weight. It is incorrect to refer to sodium chloride having a molecular weight as NaCl exists as an ionic compound (Na<sup>+</sup> Cl<sup>-</sup>) not as a molecular compound. In this case it is more precise to refer to sodium chloride’s formula weight. | The difference between formula weight and molecular weight depends on the compound. It is correct to refer to a compound such as Benzene having a molecular weight or formula weight. It is incorrect to refer to sodium chloride having a molecular weight as NaCl exists as an ionic compound (Na<sup>+</sup> Cl<sup>-</sup>) not as a molecular compound. In this case it is more precise to refer to sodium chloride’s formula weight. | ||
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'''Avogadro’s Number & mole''' | '''Avogadro’s Number & mole''' | ||
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<center> <math>n=\frac {m}{FW}</math> </center> | <center> <math>n=\frac {m}{FW}</math> </center> | ||
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'''Molarity – Molar Concentration''' | '''Molarity – Molar Concentration''' | ||
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'''Primer Calculations''' | '''Primer Calculations''' | ||
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'''Weight / mole Percentage''' | '''Weight / mole Percentage''' | ||
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<math>Cl=\frac {1}{2}*100=50%</math> | <math>Cl=\frac {1}{2}*100=50%</math> | ||
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'''Density and Specific Gravity''' | '''Density and Specific Gravity''' | ||
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D<sub>2</sub> = Density of H<sub>2</sub>O @ 4°C = 1.00g/cc | D<sub>2</sub> = Density of H<sub>2</sub>O @ 4°C = 1.00g/cc | ||
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'''Molarity, Specific Gravity and Percentage Composition''' | '''Molarity, Specific Gravity and Percentage Composition''' | ||
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! style="width: 150px;"| Chemical Name || style="width: 150px;"| Formula weight || style="width: 150px;"| Percentage Composition || style="width: 100px;"| Specific | ! style="width: 150px;"| Chemical Name || style="width: 150px;"| Formula weight || style="width: 150px;"| Percentage Composition || style="width: 100px;"| Specific Gravity || | ||
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Percentage composition means | Percentage composition means ''x''g of pure compound per 100g of solution, i.e. 37g/100ml = 37%. | ||
To calculate the molarity, the mass of pure compound is needed; however the solution’s specific gravity needs to be taken into account, and the volume; which we’ll take to be 1L. | To calculate the molarity, the mass of pure compound is needed; however the solution’s specific gravity needs to be taken into account, and the volume; which we’ll take to be 1L. | ||
Latest revision as of 14:35, 8 September 2007
Other Bits - Useful Molecular and Chemical Equations
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Useful Molecular and Chemical EquationsFormula Weight & Molecular Weight Formula weight (FW) and molecular weight (MW) are calculated by summing the atomic weights (AW measured in atomic mass units, amu) of the individual atoms.
Avogadro’s Number & mole 1 mole of atoms / molecules has a mass equal to the atomic / molecular weight in grams. e.g. 1 mole (1mol) NaCl is the number of molecules in 58.44g of NaCl. (1mol NaCl = 58.44g) Avogadro’s number is the number of atoms / molecules in 1 mole of any substance, which is equal to 6.02214x1023.
Molarity – Molar Concentration Molarity is the number of moles of solute per litre of solution. e.g. 6 molar (6M) HCl is equal to 6 moles (6mol) of HCl per litre (L). (6M HCl = 6mol/L)
Based on the previous two equations:
Primer Calculations Primers are dissolved in sterile distilled water (sdH2O) to a concentration of 500pmol. Use one of the following to determine what volume of sdH2O to use:
Weight / mole Percentage The percentage weight of an element in a compound is calculated using the atomic weight and formula weight.
[math]\displaystyle{ \frac {AW}{FW}*100=%weight }[/math] Percentage weight of Cl in HCl: [math]\displaystyle{ Cl=\frac {35.45}{36.45}=97.26% }[/math]
Similarly, mole percentage is a ratio.
[math]\displaystyle{ \frac {x}{T}*100=%mole }[/math] Percentage mole of Cl in HCl: [math]\displaystyle{ Cl=\frac {1}{2}*100=50% }[/math] Density and Specific Gravity Density is the mass of a substance per volume.
Specific gravity is a unitless ratio, so for all purposes; SG ≡ D. Cubic centimetres are equivalent to millilitres; cc ≡ mL.
D2 = Density of H2O @ 4°C = 1.00g/cc Molarity, Specific Gravity and Percentage Composition Calculating Molarity from specific gravity and percentage composition:
Percentage composition means xg of pure compound per 100g of solution, i.e. 37g/100ml = 37%. To calculate the molarity, the mass of pure compound is needed; however the solution’s specific gravity needs to be taken into account, and the volume; which we’ll take to be 1L.
Where 1L = 1000cc For HCl: [math]\displaystyle{ m=\frac {1.18*1000*37}{100}=436.6g }[/math] Therefore: [math]\displaystyle{ M=\frac {436.6}{1*36.45}=11.97mol/L }[/math]
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