Food Science: Element Composition

• Fundamentals of Science - Level 6 Certificate in Food Science and Technology
• Session: Element Composition

Learning Objectives:

• To calculate the percentage of elements in a molecule/compound (elemental analysis)
• To use the Avogadro number to calculate the number of elements based on weight
• To calculate the number of elements using the mole
• To describe the physical process required to get a solid to dissolve in a liquid

Chemical Composition Of The Human Body:

• The human body is composed of 62% water, 16% protein, 16% fat, 6% minerals, and 1% carbohydrate.
• Oxygen accounts for 65% of the elemental composition
• Carbon accounts for 18%
• Hydrogen accounts for 9.5%
• Nitrogen accounts for 3.2%
• Calcium accounts for 1.5%
• Phosphorus accounts for 1.2%
• Potassium accounts for 0.4%
• Sulfur accounts for 0.2%
• Sodium accounts for 0.2%
• Chlorine accounts for 0.2%
• Magnesium accounts for 0.1%
• Other elements account for >1%

Elemental Analysis (EA)

• Elemental Analysis (EA) is a specialized technique used to identify chemical compounds
• It necessitates a combination of specialized techniques.
• Elemental Analysis is a primary method because it helps to calculate the theoretical percentage (%) of elements such as C, H, N, O, etc., in a sample
• It measures the percentages of elements in the sample using a Gas Chromatogram
• Finally compares to the theoretical value.
• Theoretical composition of ethanol is C 52.2%, H 13.0%, and O 34.8%

Elemental Calculation Steps

• The molecular formula for ethanol is C2H5OH.
• Ethanol contains 2 carbons, 6 hydrogens, and 1 oxygen atom.
• To calculate the mass of each element using the atomic mass : Carbon 2x12=24 amu, Hydrogen 6x1 = 6 amu, Oxygen = 1x16 = 16 amu
• Total all the masses: 24 + 6 + 16 = 46
• % C = (24/46)x100 = 52.17%, % H = (6/46)x100 = 13.0%, and % O = (16/46) x 100 = 34.78%

Acceptable EA Measurements

• Measurements help identify the compound and its purity
• What are acceptable values will depend on the scientific journal
• Typical values can vary from ±0.4% down to ± 0.1%.
• For a theoretical calculation for C=54.0%, the range of 0.4% = 54 x 0.004 = 0.22%
• Range for C= 54 (+/-) -0.22 = 53.78% and C=54.22% with an acceptable range = 53.78-54.22%
• If the experimental result for Carbon was 53.92%, the result is good
• If the experimental result was 54.35%, the sample is not acceptable due to contamination

Comparing Carbon Dioxide and Carbon Monoxide

• C=12 amu and O=16amu
• Compare CO2 and CO using %C and %O
• Range and acceptable for ±0.4%
• Identify the compound with the highest percentage of carbon
• Identify the compound with the highest percentage of oxygen

Atomic and Molecular Mass

• The periodic table has the atomic mass in amu
• Grams are used in every day life
• amu is too small to measure on a weighing balance
• An individual atom or molecule weights very little!
• The ability to count atoms and molecules is achieved a simple system
• 1 amu = 1.66054 x 10 -24 g is the relationship of amu to gram

Mass and Number

• Carbon has a mass of 12amu, and Oxygen has 16 amu
• amu is replaced with g: 12g of C and 16g of Oxygen achieved
• Number of atoms of C in 12g or O in 16g cannot be determined if the number of atoms in 16g O would be the same as 12g of C.

Avogadro number and the Mole

• New system developed by scientists.
• Started in 1896 by German Chemist Wilhelm Ostwald.
• A physicist Jean Baptiste Perrin's made the first measurement.
• Measurement found to be 6.022 x 1023
• This number is called the Avogadro Number
• When the atomic mass is converted to g the number is called the "Mole”
• One mole (1 mol) of a substance contains 6.02 x 1023 particles of the substance.
• The number 6.02 x 1023 is called the Avogadro Constant.

Moles

• 1 mole of Oxygen atoms weighs 15.994g and contains exactly 6.022 x 1023 oxygen atoms.
• The Atomic mass of hydrogen is 1.008 amu.
• Therefore, 1 mole of Hydrogen atoms weighs 1.008g and contains 6.022 x 1023 hydrogen atoms.
• 1 mole of Iron (Fe) has a mass of 55.8g, and 1 mole of Aluminium (Al) has a mass of 27.0g.
• Both cases contain Avogadro's number of atoms

Moles Calculations

• The concept of the Mole: used for the following calculations
• The number of moles in any given mass of an element
• The number of atoms in any given mass of an element
• The mass of a single atom of an element
• Calculate the number of moles of carbon atoms, and the number of individual carbon atoms in 20.0g of carbon, (e.g. graphite).
• 1 mole of carbon atoms has a mass of exactly 12g.
• Resulting in 20.0 / 12.0 = 1.67 moles of Carbon atoms
• 1 mole consists of Avogadro's number of atoms: i.e. 6.022 x 1023 atoms
• 1.67 moles of carbon atoms (i.e. 20.0g) contains 1.67 x 6.022 x 1023 = 1.01 x 1024 atoms in 20.0g of carbon

How do Compounds Dissolve in Liquids

• A solution has only one phase with no solids or cloudy appearance
• A compound/substance dissolves by the solvent molecules surrounding individual molecules, with no solid material
• Each individual molecule of the compound is surrounded by groups of solvent molecules.
• Solubility is when the solid compound is split into individual molecules
• Then each individual molecule is surrounded by molecules of the solvent
• This is called a solvent sheath
• Guidelines for predicting compounds dissolve have to conform to like dissolves like

Making a Solution

• Most chemical reactions occur in solution
• Materials should be dissolved before starting a chemical reaction
• Requires question of what solvent to use?
• The question is tough because most reactions involve carbon, which is not soluble in water
• The solute is the substance you want to dissolve
• The solvent is the liquid

Like Dissolves Like

• Chemists use the general guideline: "Like Dissolves Like."
• This means a polar solvent will dissolve a polar substance like solvent.
• This similarly means a non-polar solvent will dissolve a non-polar substance.

Polar Solvent Dissolves Polar Substance

• The polar solvent breaks the polar bond of the solute in a solid state.
• This allows the individual solute molecules to be surrounded by the solvent
• The result is always a solution
• "Like Dissolves Like”

Non Polar Solvents

• Polarity will determine if the non polar solvents will not dissolve polar substances
• The non polar solute has no partial charge
• Therefor it cannot break the polar bonds of the solvent solute
• The result indicates non polar solvent remains as a solid, and does not dissolve.
• "Like Dissolves Like" condition is not met

Non polar solvent dissolves non polar substance

• The non polar solute does not need to break any bonds in the non polar solvent
• Therefore the non polar solvent molecules can surround the non polar solute.
• Finally achieving the "Like Dissolves Like” condition!

Polar Solute will not dissolve non polar substance

• The non polar solute has no charge to break the bonds of the polar substance.
• The non polar solvent molecules cannot surround the non polar solute.
• "Like Dissolves Like" condition is not achieved, and the solution does not mix

Polarity and Solubility

• Ionic compounds and polar molecules dissolve in polar solvents
• Organic molecules and non polar molecules dissolve in non polar solvents, like dissolves like but will not be achieved!

Choosing a Solvent

• Solvents with alcohol groups: typically polar
• Solvents with no OH groups: typically non polar
• A detailed index can be followed to measure solvent polarity

Conclusion

• It is possible to calculate the percentage of elements in a molecule/compound (elemental analysis)
• To use the Avogadro number to calculate the number of elements based on weight.
• To calculate the number of elements using the mole.
• To describe the physical process required to get a solid to dissolve in a liquid (Like Dissolves Like).