Chemistry of Baking

Elements Compounds and Mixtures

Elements and Compounds

2Mg₂ + O₂ —> 2MgO_(s) + CO_{2 (g)}

_{(element) (molecule) (compound ionic) (compound molecule)}

Diatomic:

A lot of non-metals are diatomic

H₂, N₂, F₂, Cl₂, Br₂, I₂

Chemical Element: A neutral substance that cannot be broken down into simpler substances using chemical bonds

Compound: is a pure substance formed when two or more chemical elements combine together. A compound has different properties from its component of elements.

Molecule: They consist only of atoms that contain the same number of protons although the atoms can contain a different number of neutrons. There are 188 known chemical elements.

Mixtures

Mixture: is a physical combination of pure substance which can be separated into its pure components by physical means. Contain more than one element and/or compound that are not chemically bonded so keep their individual properties.

Homogenous mixture: all the components are in the same phase (air, coffee). They have uniform properties

Heterogenous mixture: The components are in different phases (oil and water, sand and salt). Non uniform properties.

Emulsion: Two immiscible mixtures that are turned into a mixture, where one mixture are tiny balls of liquid dispersed in another (milk which is fat and water )

Immiscible: Two mixtures that cannot make a homogenous mixture when mixed together.

Saturation: Maximum solute that a solvent can hold

Separating Mixtures

Fractional distillation: Allows to separate liquids of close temperature. Where the one with higher boiling point will vaporize but then condense back down as it has to travel more compared to normal distillation

Dissolving and evaporate: One use case is to separate salt from sand. Sand is not soluble by water so by dissolving the salt in water and using funnel paper to separate the sand from the water. Then evaporate water and be left with salt

Dissolve and Filter: Separating sand from salt. Mix the salt with water and then filter the solution through filter paper and funnel finally pour mixture into the filter paper rinse with water to dissolve extra salt. Left with only sand in funnel

Distillation: Heating of a liquid and then let it condense it back. Lower boiling point solution rises first and condenses while high boiling points stays in round bottom flask. Example Separating Alcohol from water. Only useful if boiling points are quite far apart

Fractional Distillation: With closer boiling points or more than two solutions. When ethanol boils at 78 water vapor would also go with it contaminating. Meaning that a fractionating column is needed to condense the water vapor and return to round bottom flask

Magnet: For example iron from sulphur use strong magnet to attract the iron from sulphur.

Separation funnel: (immiscible liquids). For example oil and water, oil is at the top water at the bottom, water goes down while oil stays

Chromatography: Separating components of different mixtures. This is because they move differently when in a solution. Such as different dyes, put dyes on chromatography paper, allow solvent to rise and the dyes separate.

Gel electrophoresis: Applying electric fields to separate based on charge and size as they move faster or slower depending on size and charge. Some things that can be separated amino acids move differently than protein so then separated

KMT and States

States

Melting: Solid transforming to liquid (Endothermic)

Freezing: Liquid transforming to solid decrease in potential energy (exothermic)

Evaporation: Phase change from liquid to gas at lower than boiling point, Increase in potential energy. Occurs at the surface molecules to gas. (Endothermic)

Vaporization: Phase change from liquid to gas, increase in potential energy (endothermic)

Crystallization: Liquid to Solid. Saturated solution allow to cool and as it cools and the solute is no longer dissolved. Can be better than evaporation to remove solvent. (exothermic)

Boiling: Gas to liquid. When vapor pressure=external pressure. produces gas bubbles that rises to the top of the liquid. (Endothermic)

Condensing: Gas to liquid (Exothermic)

Sublimation: Solid to gas directly without being in liquid. Example is dry ice, from solid dry ice to CO₂ gas directly (Endothermic)

Deposition: Gas to solid without being in liquid. Example is snowflakes, from water vapour to solid snowflakes (Exothermic)

Boiling point of water:

As water heats up some molecules have enough energy to escape the intermolecular forces and turn into a vapor (gas). The gas molecules cause a pressure called the vapor pressure. As the water heats up more and more particles escape the surface of the liquid to become a vapor.

Boiling: Water vapor pressure= (100kPa)=atmospheric pressure =(100kPa)

The lower the pressure, the lower the boiling point for water and vice versa. Example if pressure is 120kPa then boiling pure water boils at 120C.

Kelvin: Increase at the same rate of celcius but starts at absolute zero which is -273C. To convert add or subtract 273

Energy:

When a substance in undergoing a phase change the temperature remains constant which show that there is no change in E_k. The energy changed is E_p due to the change in the inter molecular forces.

Kinetic Molecular Theory (KMT)

Postulates of the Kinetic Molecular Theory:

1. Gases have a very small volume (if compressed volume is negligible)

2. Gases are constantly moving at high speeds in random, but in straight line paths (Brownian motion)

3. Gases experience no electrostatic attractions between molecules.

4. The speed of a gas molecules is directly proportional to its mass and Temperature

   E_k=1/2mv²

5. Perfectly elastic collisions

These assumptions are good for ideal gases and are used quite often with little error. However, when one needs to be exact you must account for the fact that REAL gases have mass and experience electrostatic attraction.

Temperature and Ek

Temperature (T) is a measure of average kinetic energy (E_k)

Temperature is not Thermal Energy. Thermal

Kelvin+273=Celsius

Celsius-273=Kelvin

Goes up the same rate

Heat goes in and out cold does not go in and out.

Enthalpy change (∆h):

• The heat usually transferred either into or out of a system

• Is equal to the change of energy of chemical bonds

• Is only applied to reactions that occur at standard pressure (100kPa)

Introduction to the mole

Chemical formulae: Letters are symbols for elements

Ionic compounds: For ionic compound put the cation (positive) and then the anion (negative)

Covalent compound: Exact number of each element present in molecule order doesn’t matter

Hydrated compounds: Ionic compounds with water attached (electrostatic attraction) to form a larger compound)

6.02×10²³ is Avogadro’s number with he number called a mole. A mole of something equals 6.02×10²³ quantity of that thing.

Atomic Mass

Atomic mass

Ratio of the atomic mass per isotopes of an element compared to one twelfth of the mass of the C-12 isotope.

Relative Atomic Mass:

Ratio of the atomic mass per atom of an element compared to one twelfth of the mass of the C-12 isotope.. Dependent on the naturalabundance of different isotopes of an atom.

Empirical and Molecular Formulas

Percentage composition:

It is the percentage by mass of the species in a chemical formula

Empirical formula

1. is the smallest whole number ratio of atom of each element in a compound

2. is applicable to both ionic and covalent compounds

Method

% to mass, mass to moles, divided by the smallest ratio, x to make it whole.

Molecular formula:

• Is the actual of atoms of each element in the compound

• is applicable to only ionic compounds

• can sometimes be the same as the emperical formula

• is always a whole number multiple of the empirical formula

• Therefore the emperical formula is CH₂. The molecular formulae are CH₂,C₂H₄

Chemical Equations

Reactant: a substance that changes in a chemical reaction; a substance that is present starting a chemical reaction

Product: a substance that is created by a chemical reaction; a substance present after the reaction

Net ionic equations show only the ions that are involved in the reaction, does not include the spectator ions.

Word equations are equations with chemical symbols and numbers replacing the names of the reactants and products

Neutralization reactions:

An acid and base produce a salt that contains the anion of the acid and the action of the base. monoprotic acids give one hydrogen ion. Diprotic acids like H₂SO₄ give two hydrogen ions (require two OH^-)

Acid- Carbonate Reactions

Acids react with carbonates and hydrogen carbonates in a type of neutralization

Solubility Rules:

Equipment

Number in Image to know : 1,2,3,4,5,6,13,14,16,18,24,26,27,28,29,30

Equipment uncertainty is (smallest measurement)/2 for analog

Digital uncertainty is equal to smallest reading

Sometimes need to use manufactures uncertainty in digital devices

How a standard aqueous solution can be prepared:

Determine the number of moles of solute needed to make desired concentration.

Calculate and then using that measure the amount of mass needed

Add solute to small beaker and add sufficient distilled water to fully dissolve the solute (has to be less than required volume)

Pour the solute and solvent into a volumetric flask

Fill up the volumetric flask up to the line using distilled water (use the beaker to fill

Invert shake volumetric flaks

Molar concentration

Solute: The substance that is dissolved

Solvent: the substance that is in liquid form the substance the solute is dissolved in

Solubility:the amount of a solute that will dissolve in a given volume of the solvent

Saturated a solution in which no more solute will be dissolved at that temperature

Precipitate When a solid is produced in a chemical reaction in a solution it is called y

Concentration (C) is the amount in moles contained with a given volume (V) of a solution

Molarity (molar Concentration) the molarity of a solution is the concentration in moldm^-3

Avogrado’s law: At constant temperature and pressure, a volume of gas always has the same number of particles

1 mole =22.7dm³ at STP (0 and 100kPa)

Limiting Reagents

Identifying limiting reagent:

1. Take the number in the problem and divide by the coefficeint from the balanced reaction

2. The smallest ratio gives the limiting reagent

Percentage yield

Theoretical Yield:  The amount of the product calculated using stoichiometry

Actual Yield  the amount of product actually made when the reaction is done in a laboratory

Percent Yield The amount of product actually produced divided by the amount of product that could be produced theoretically (as a percentage)

Atom Economy

Percentage Yield of the mass of product that is desired over total mass of reactants

Exothermic and Endothermic Reactions

1. Exothermic reaction

• ∆h is negative

• Chemical potential→ heat energy

• Energy has been given to the surroundings

2. Endothermic Reaction

• ∆h is positive

• heat energy → chemical potential

• Energy has been absorbed from the surroundings

Activation energy: minimum energy required for a collision reaction to be successful

Enthalpy change: Difference between chemical E_p of Reaction and Products

Calculation of Enthalpy Changes

• Enthalpy changes (ΔH) are related to the number of moles in the reaction. If all the coefficients are doubled, then the value of ΔH will be doubled.

• When a reaction is carried out in aqueous solution, the object will gain or lose heat from (or to) the reactants.

• Therefore, the change in energy (ΔH) can be calculated from Q = m x c x ΔT.

• The ΔH value can then be calculated back to find the molar enthalpy change for the reaction.

• Calorimeters are used to measure the heat released (Q system) by a chemical reaction.

• A device called a calorimeter is used to measure the heat released in a combustion reaction. 

• Heat absorbed = (mc ΔT) liquid + (mc ΔT) calorimeter

1. Density of solution=density of water @ 25C

2. Specific heat capacity of solution is the same as H₂O (4.18Kjkg^-1K^-1)

Hess’s Law

Hess’s law: it doesn’t matter how many seps takes for a reaction to occur, or what those steps are, the enthalpy will be the same.

Usually before reactions are added together, some of them must be reversed and/or multiplied by a factor n in order that they sum to the desired reaction. in this process the rules are:

1. Whenever you multiply a reaction by n, ∆H for the reaction is also multiplied by n.

2. If you reverse a reaction, ∆H changes sign.