Separation Techniques and Solutions Flashcards
mixture
in a mixture 2 or more substances are physically mixed together.
this means that no chemicla reaction/change as taken place and no new substances have been formed. the substances are simply near each other in the same space. the substances being mixed can be in any state of matter when forming a mixture.
states of matter
gas, liquid, solid
heterogenous mixtures
they occur when 2 or more substances are mixed and the composition is not uniform throughout the mixture.‘in different states or phases’ A mixture containing two or more phases or states of matter.
you typically see that there are different substances mixed together
e.g.: sand and sugar, a salad, oil and water
homogenous mixtures (solutions)
occur when 2 or more subatnces mix with a uniform composition at the particle level. ‘in the same state or phase’ A mixture containing one phase or state of matter.
to the naked eye, a homogenous mixture appears as one substance, though actually multiple substances are present.
e.g.: salt water, the atmosphere, carbonated beverages, metal alloys
what are simple solutions made of?
solutes and solvents
solute
the minor component in a solution, dissolved in the solvent.
solvent
the larger component in a solution, able to dissolve a solute
aqueous solution
solutions where water is the solvent is referred to as an aqueous solution.
they play a major role in many chemical reactions snd in the human body. the symbol used in chemical equations to represent an aqueous solution is (aq).
how to seperate a mixture? (general idea)
since mixtures are only physically mixed together, it should awlays be possible to seperate mixtures into their components by exploiting differences in physical properties.
physical properties
propreties that can be measured or observed without changing the chemical composition of the substance. they include:
* melting point
* boiling point
* volatility
* solubility
* conductivity
* magnetism
* hardness
* colour
^^ many of these depend on the types and relative strengths of the interparticle (intermolecular) forces/attractions bteween the particles of a substance or mixture.
separation techniques
for solid in liquid mixtures
homogenous:
* evaporation
* distillation
* entrifugation
heterogenous
* sedimentation/gravitation
* filtration
* magnetic seperation
* fractional distillation
for liquid in liquid mixtures
homogenous:
* simple or fractional distillation
* chromotography
heterogenous:
* seperating funnel
filtration
This technique is used to separate an insoluble solid from a liquid by passing the mixture through a porous barrier, such as filter paper.
the substance left in the filter paper is called the residue and the liquid taht comes through is called the filtrate
separating funnel
Separating liquid from an insoluble liquid based on differences in their densities.
The denser liquid settles at the bottom and can be drained off first, while the less dense liquid remains on top. e.g. oil is less dense than water, where water would be drained off furst using this technique.
evaporation
a type of vaporization that occurs on the surface of a liquid as it hanges into the gas phase. can be used to separate solutes dissolved in a solvent by boiling the solution. the solvent gets vaporised leaving back solute.
solvation
solvation is essentially the process that happens when something dissolves, but with a focus on what the solvent molecules are doing. Solvation is the process by which solvent molecules surround and interact with solute particles when a substance dissolves. In this process, intermolecular forces between the solute and solvent, such as hydrogen bonding, dipole-dipole interactions, or ion-dipole forces, stabilize the solute particles in solution. Solvation is essential in determining solubility and reaction mechanisms in solutions.
simple distillation
Simple distillation is a method used to separate a liquid from a mixture based on differences in boiling points. The mixture is heated until the liquid with the lowest boiling point evaporates, then the vapor is cooled and condensed back into a liquid, called the distillate.
the components being separated are miscible, meaning they mix completely to form a homogeneous mixture. This method relies on differences in boiling points rather than immiscibility.
fractional distillation
Fractional distillation is a separation technique used to separate a mixture of miscible liquids with closely spaced boiling points (less than 25°C difference).
Fractional distillation uses a fractionating column, a vertical tube filled with materials like glass beads or plates. This column increases the efficiency of separation by creating multiple stages of condensation and evaporation as the vapor rises.
As the mixture is heated, the liquid with the lowest boiling point evaporates first. In the column, the vapor cools slightly and condenses on the surfaces, then re-evaporates as it absorbs more heat. Each cycle progressively purifies the vapor, ensuring better separation of liquids with close boiling points before reaching the condenser.
e.g. water (100C b.p) and ethanol (78C b.p)
chromatography
Paper chromatography is used to separate mixtures of soluble substances based on their relative attractions involving intermolecular forces to mobile and stationary phases.
Chromatography relies on two different ‘phases’:
* the stationary phase, which in paper chromatography is very uniform, absorbent paper
* the mobile phase is the solvent that moves through the paper, carrying different substances with it
The different dissolved substances in a mixture are attracted to the two phases in different proportions. This causes them to move at different rates through the paper. the choice of solvent (and its polarity) will affect how well the different
components separate out.
for IB, you’re only required ot know about paper chromatography and thin layer chromatography (TLC) where the only difference is the stationary phase (paper chrom. uses paper, TLC uses silica gel)
chromatogram
Separation by chromatography produces a chromatogram.
A paper chromatogram can be used to distinguish between pure and impure substances:
* a pure substance produces one spot on the chromatogram
* an impure substance produces two or more spots
A paper chromatogram can also be used to identify substances by comparing them with known substances. Two substances are likely to be the same if:
* they produce the same number of spots, and these match in colour
* the spots travel the same distance up the paper (have the same Rf value)
Rf values
The Rf value of a spot on a chromatogram is calculated using:
Rf = distance travelled by substance/ distance travelled by solvent
Rf are given as rounded decominals and are always values between 0 and 1.
* An Rf value of 0 would mean that yhe substance is insoluble in the mobile phase (the solvent being used) and so the spot remains on the start line.
* an Rf value of 1 would mean that the substance has moved as far as the solvent front, so it’s very strongly attracted to the mobile phase. though this is rare.
water as a solvent
Types and properties of solutions
water is a highly polar molecule, meaning it has a partial negative and a partial positive charge at its ends. Because of these partial charges, water iis an effective solvent for many compounds that also contain charges, such as polar covalent compounds (partial charges) and ionic compounds (full charges)
water insoluble
Types and properties of solutions
covalent (molecular) compounds that are largely non polar, such as oil and hydrocarbon compounds, do NOT mix with water and therefore are immiscible. general rule is that giant covalent structures are completely insoble in water (or any solvent).
which type of compound? what happens?
water soluble substance
Types and properties of solutions
polar covalent compounds are usually miscible or soluble with water if the molecules can form hydrogen bonds with water molecules. When polar covalent compounds dissolve, the molecules are surrounded by water molecules and spread out evenly throughout the solution. The molecules, however, stay intact. Therefore, they do not dissociate apart into atoms or ions.
aqueous solutions of ionic compounds
Types and properties of solutions
When ionic compounds dissolve in water, the individual ions are pulled apart by ion-dipole interactions and surrounded by water molecules. The ions are said to fully dissociate, or separate, away from each other. This means that solutions of ionic compounds are full of separated, free moving ions.
forming electrolytes
electrolytes and non-electrolytes
Types and properties of solutions
Due to their dissociation, solutions of ionic compounds will conduct electricity and can be referred to as electrolytes. This is because they contain free moving charges (ions, not electrons!). electrolytes can conduct electricity.
Solutions of molecular compounds, however, contain intact, neutral molecules. Therefore, they do not contain any free moving charges and can be referred to as non-electrolytes.
summary of solubility and aqueous conducitivity in terms of bonding types of compounds
presented as a table in the packet
water solubility:
1) metallic: none
2) giant covalent: none
3) covalent molecular: depends on polarity
4) ionic: usually
aqueous conductivity:
1) metallic: N/A
2) giant covalent: N/A
3) covalent molecular: none/poor/low
4) ionic: good/high
aqueous conductivity
the ability of an aqueous solution (water with dissolved substances) to conduct electricity. This depends on the presence of ions (charged particles) in the solution. The more ions present, the better the solution conducts electricity.
relates to electrolytes and non electrolytes
nonpolar compound solubility
when water is not the solvent
Compounds that are not polar enough to dissolve in water can usually be dissolved by other solvents that are less polar than water. These molecules interact with the molecules of other substances with dipole-dipole forces and/or London Forces.
polar/aprotic solvents
Solvents can be somewhat polar, meaning they can interact with
dipole-dipole forces but not hydrogen bonding. they can dissolve polar compounds and ions.
polar/protic solvents
solvents that are polar and also contain (H-NOF bonds) hydrogen atoms attached to electronegative atoms, such as oxygen or nitrogen. These hydrogen atoms are capable of forming hydrogen bonds with other molecules, which influences the solvent’s behavior in chemical reactions. they can dissolve polar compounds and ions.
e.g. water, ethanol, most alcohols
many organic solvents (completely non polar)
miscible with other non polar substances.
thin layer chromatography (TLC)
Thin Layer Chromatography is similar to paper chromatography, but the stationary phase is silicon compound paste, spread on a thing sheet of plastic. The spots often need to be visualized using dyes or ultraviolet (UV) lights.
solubility
the ability of a substance (solute) to dissolve in a solvent, forming a homogeneous mixture called a solution. The extent to which a solute dissolves depends on factors like the nature of the solute and solvent, temperature, and pressure.
When a substance (typically we are focused on solid solutes) is soluble in water, there is generally a maximum amount of it that can be dissolved into a given amount of water at a given temperature. a solution can be referred to as:
* unsaturated solution: more solute dissolves
* saturated solution: no more solute dissolves
* supersaturated solution: becomes unstable, crystals form
not on this test
effect of termperature on solubility
While not true for all substances, water solubility usually increases with increasing water temperature. The water molecules have greater kinetic energy and are able to keep more solute particles separated. The exact relationship is unique for each substance and must be determined experimentally.
*Degrees of saturation and the effect of temperature on solubility are not a huge focus for the IB Chemistry course, however, they are useful terms and concepts to be aware of.
concentration
The concentration of a solution is the amount of solute per a certain amount of solution (or per a certain amount of solvent). A solution with a higher concentration has more solute particles in a given amount of solvent than one with a lower concentration.
a solution is dilute if it has a relatively low concentration and concentrated it has a relatively high concentration of solute. these terms are only useful for giving a vague sense of concentration, and in chemistry it is preferable to express concentration quantitatively, with a unit.
equation C = n/V
units: moles solute/ dm^3 of solution –> mol dm^-3
*Note that brackets [ ] are often used to indicate “concentration.” For example,
[NaCl] is a shorthand to mean “the concentration of NaCl.”
most precise glassware for measuring volume
Volumetric flask: are useful for measuring certain volumes of liquid with a very high degree of accuracy. common sizes are 50 cm3, 100cm3, 250cm3, 500cm3, 1.0 dm3.
volumetric flasks cannot be used for any otehr volume but the one its is marked for
Graduated pipettes/pipettes: useful for measuring lots of differnt small volumes of liquid with a high degree of precision.
downside is that they are somewhat slow and the reading are often more challenging to take
less precise glassware for measuring volume
graduated/measuring cylinders: are useful for measuring lots of differnt volumes of liquid quickly and with a reasonably high degree of precision.
fine for less formal lab work, but should be avoided on IB exam questions and IAs when a better alternative is reasonable and available
non-measurment glassware
beakers: useful for holding and pouring liquids. they should never be used to measure volumes of liquids as they are very imprecise
erlenmeyer/ conical flasks: very useful for holding liquids, especially those that need to be sealed off as they have a narrow neck. they should never be used to measure volumes of liquids as they are every imprecise.
dilution
Dilution is a technique for lowering concentration. More solvent is added to a solution, which lowers the ratio of solute-to-solvent. In dilution, the change in volume & the change in concentration are inversely proportional. e.g. Volume is doubled –> Half the initial concentration
Volume is tripled –> One third the initial concentration
Volume increased 10x –> 1/10th Initial concentration
equation for more complex changes in volume and concentration:
C1V1 = C2V2
1 = initial solution
2= target solution
acids and bases
A simplified way of considering acids and bases is that:
* acids are solutions containing H+ ions
* bases are solutions containing OH- ions.
While not the definition we will use later in the course, it is a useful idea to have for now.
* strong acids are often polyatomic anions bonded to hydrogen. The number of hydrogens matches the charge on the polyatomic anion.
* The strong bases are usually ionic compounds, with a metal cation balanced by a given number of hydroxide ions.
Strong species are defined as those that fully dissociate (or ionize) in solution (with water). This means that they react with water molecules, yielding ions in solution. In this way, acids and bases are electrolytes and share similarities with the solutions of ionic compounds.
*Some acids and bases can yield more than one proton, or hydoxide ion, per
molecule. These are referred to as diprotic or tripotic species.
The pH Scale: Simplifying Acid & Base Concentrations
pH and pOH are used to express acidity and alkalinity using relatively simple numbers. They are related values and are both logarithmic in nature:
*we did not go over this in class
metal alloys
A metal alloy is a homogenous mixture (or a “solution”) of 2 or more metals (or of nonmetals into a metallic lattice).
Although the atoms and ions of the different elements interact via metallic bonds, alloys are not technically considered metallic compounds. This is because compounds have defined proportions (mole ratios) of each element.
Alloys on the other hand, occur with no fixed ratio of the relevant elements. This allows for essentially infinite subtle changes in percent composition of elements in alloys.
examples:
* Stainless Steel: An alloy of iron (Fe), carbon (C), and chromium (Cr), sometimes with nickel (Ni) or molybdenum (Mo).
* Brass: An alloy of copper (Cu) and zinc (Zn).
* Bronze: An alloy of copper (Cu) and tin (Sn).
enhanced properties of metal alloys
The inclusion of the other metal (or nonmetal) atoms in the metal lattice gives many alloys “enhanced properties” compared to pure metal elements.
While each alloy is unique, the most important idea is that the different ions and atoms have different ionic and atomic radii. This means that when they mix, the other elements end up distorting the regular lattice arrangement of the pure metal. (For the IB) fair to consider that this happens because the particles of the other elements fill in the spaces between the pure metal’s ions.
usually have these properties compared to pure metals
1) harder: by fitting particle of other elements in between the metals, it makes it more difficult for the layers of metal ions to slide past each other.
2) lower melting points: other elements act as impurities, disrupting the normal metallic bonds between the metal’s atoms - whereas pure metals are arranged in regular, repeating patterns that allow for strong metallib bonds. (not universal where some ca have high melpting points.)
3) more resistant to errosion: since the paryicles are filling in gaps in the metal lattice, it can make it more difficult for other elements, especially oxygen, to get in contact with the metal particles. additionally, the other elements can sometimes form compounds with oxygen that form a prptetcive layer on the surface of the metal, preventing metal atoms underneath from reacting.
ratios
diferrence between compounds and mixtures
compounds consist of atoms of different elements chemically bonded togetehr in a fixed ratio.
mixtures contain more than one element or compound in no fixed ratio, which are not chemically bonded and so can be separated by physical methods.
Pure substance
- a single substance made of only 1 type of particle
Elements
- the primary constituents of matter, which cannot be broken down into simpler substances
Compounds
- consist of atoms of different elements chemically bonded together in a fixed ratio
