Percent Composition

Percent Composition

The percentage by mass of each element present in a compound

%Element = ((mass of element)/(mass of compound))*100%

Formula for Percent Composition

help identify unknown chemical formulas

Purpose of Percent Composition: Used to determine the relative amount of each element in a compound and to ….

Constituent Element

An element that makes up part of a compound.

Percent Composition from Experimental Data

A method that uses measured masses of elements in a sample to determine the percent by mass of each element

Determining Percent Composition from a Known Formula

A method that uses atomic masses and the compound's formula to calculate the mass percentage of each element.

Formula Mass

The sum of the atomic masses of all atoms represented in a chemical formula

Molecular Mass

The mass of a single molecule expressed in atomic mass units (amu).

Molar Mass

The mass of one mole of a substance, expressed in g/mol.

To determine the mass percentage of the nutrient element, such as nitrogen, available in the fertilizer.

Why Fertilizer Manufacturers Use Percent Composition

Empirical Formula

The chemical formula showing the simplest whole-number ratio of atoms of each element in a compound

First Step in Determining an Empirical Formula

Convert the mass of each element into moles using molar masses

Moles = Mass/Molar mass

Mass to Moles Conversion Formula

Chemical formulas represent numbers of atoms, not masses

Why Masses Must Be Converted to Moles

Mole Ratio

The ratio of the numbers of moles of elements in a compound.

Divide all mole values by the smallest mole value obtained.

Determining Empirical Formula Subscripts

Tentative Empirical Formula

The formula obtained immediately after dividing all mole amounts by the smallest mole amount

Whole-Number Subscripts Rule

Empirical formulas must contain whole-number subscripts

Correcting Fractional Subscripts

Multiply all subscripts by the smallest integer that converts them into whole numbers.

Convert masses of all elements to moles.

Empirical Formula Flowchart Step 1

Divide each mole amount by the smallest mole amount.

Empirical Formula Flowchart Step 2

Convert the resulting ratio into the lowest whole-number ratio

Empirical Formula Flowchart Step 3

Write the empirical formula using the whole-number subscripts.

Empirical Formula Flowchart Step 4

Deriving an Empirical Formula from Percent Composition

A method that uses percentage data instead of actual masses to determine the empirical formula

Convenient Mass Assumption Method

Assume a 100 g sample so that each percentage value becomes an equivalent mass in grams.

It allows percentage values to be directly interpreted as masses in grams.

Why a 100 g Sample is Often Assumed

Convert percentages to masses, convert masses to moles, determine mole ratios, and reduce to the smallest whole-number ratio.

Procedure for Finding an Empirical Formula from Percent Composition

Molecular Formula

A chemical formula showing the actual number of atoms of each element in a molecule.

The empirical formula gives the simplest ratio of atoms, while the molecular formula gives the actual number of atoms

Difference Between Empirical and Molecular Formula

The empirical formula and the compound's molecular mass (or molar mass)

Information Required to Determine a Molecular Formula

Empirical Formula Mass

The sum of the atomic masses of all atoms in the empirical formula.

n = (Molecular Mass)/(Empirical Formula Mass)

Formula for Determining the Molecular Formula Multiplier (n)

(Empirical Formula)_n = Molecular Formula

Relationship Between Empirical and Molecular Formulas

Glucose

C₆H₁₂O₆

Empirical Formula of Glucose

(CH₂O)₆

Hematite

• Fe₂O₃

• The mineral form of iron(III) oxide used in jewelries

Alkaloid

• A naturally occurring organic compound that contains one or more nitrogen atoms and is typically produced by plants

• Alkaloids often have strong physiological effects on humans and animals

• Commonly used as medicines, stimulants, poisons, or recreational drugs.

• Examples: nicotine, caffeine, morphine, quinine, and atropine

Solanaceae (Nightshade Family)

A family of flowering plants that includes many agriculturally important species such as potatoes, tomatoes, eggplants, peppers, and tobacco. Several members of the Solanaceae family produce biologically active alkaloids

Nicotine

• C₁₀H₁₄N₂

• Receptors it binds to: Nicotinic acetylcholine receptors (nAChRs)

• Plants that produces: Tobacco (Nicotiana tabacum) & Wild Tobacco (Nicotiana rustica)

• Effects of consuming it: Increased alertness, elevated heart rate, dopamine release, addiction, reduced appetite

• Other uses: Natural insecticide; protects tobacco plants from herbivorous insects

Caffeine

• C₈H₁₀N₄O₂

• Receptors it binds to: Adenosine receptors (primarily A₁ and A₂A)

• Plants that produces: Coffee (Coffea species), Tea (Camellia sinensis), Cacao (Theobroma cacao), Guarana (Paullinia cupana)

• Effects of consuming it: Increased alertness, reduced fatigue, improved concentration, increased heart rate

• Effects: Natural pesticide; deters insects and inhibits growth of competing plants

Morphine

• C₁₇H₁₉NO₃

• Receptors it binds to: μ-opioid receptors (primarily), κ-opioid and δ-opioid receptors (weakly)

• Plants that produce: Opium Poppy (Papaver somniferum)

• Effects of consuming: Pain relief, euphoria, sedation, respiratory depression, dependence

Quinine

• C₂₀H₂₄N₂O₂

• Receptors it binds to: Interferes with heme metabolism in malaria parasites (not primarily known for a specific human receptor)

• Plants that produce: Cinchona trees (Cinchona officinalis, Cinchona ledgeriana)

• Effects of consuming: Antimalarial action, bitter taste, may cause tinnitus and dizziness at high doses

• Other uses: Protects plants against pathogens and herbivores; used as a flavoring agent in tonic water

Atropine

• C₁₇H₂₃NO₃

• Receptors that it blocks: Muscarinic acetylcholine receptors (M₁–M₅)

• Plants that produce: Deadly Nightshade (Atropa belladonna), Jimsonweed (Datura stramonium), Henbane (Hyoscyamus niger)

• Effects of consuming: Pupil dilation, increased heart rate, dry mouth, decreased sweating

• Other uses: used medically for eye examinations and treatment of certain poisonings

Scopolamine

• C₁₇H₂₁NO₄

• Receptors that it blocks: Muscarinic acetylcholine receptors (M₁–M₅)

• Plants that produce: Jimsonweed (Datura stramonium), Angel's Trumpet (Brugmansia species), Henbane (Hyoscyamus niger)

• Effects of consuming: Prevents motion sickness, causes drowsiness, memory impairment, hallucinations at high doses

• Other uses: used medically in transdermal patches for motion sickness

Solanine

• C₄₅H₇₃NO₁₅

• Primary biological target: Disrupts cell membranes and inhibits acetylcholinesterase

• Plants that produce it: Potato (Solanum tuberosum), Black Nightshade (Solanum nigrum), Eggplant (Solanum melongena)

• Effects of consuming: Nausea, vomiting, diarrhea, stomach pain, neurological symptoms at high doses

• Other uses: Natural pesticide and fungicide; protects plants from insects, fungi, and grazing animals