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Pure chemistry 🧫⚗️💉 > Chapter 1: Experimental chemistry 🧪 > Flashcards

Chapter 1: Experimental chemistry 🧪 Flashcards

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1
Q

What is the international system of units (SI units)?

A
  • The international system of units is used as a common standard for measurements.
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2
Q

How are some physical quantities used in chemistry experiments?

A
  1. Mass
    - SI unit: kilogram (kg)
    - Other units: Gram (g), Tonne (t)
    - Conversion of units: 1kg = 1000 g
    1t = 1000 kg
    - Apparatus: Beam balance, and electronic balance (accuracy +/- 0.1g)
  2. Time
    - SI unit: Second (s)
    - Other units: minute 9min), hour (h)
    - Conversion of units: 1 min = 60 s, 1 hour = 60 min
    - Apparatus: Analogue stopwatch (accuracy +/- 0.1s)
  3. Temperature:
    - SI unit: Kelvin (k)
    - Other units: Degree Celsius (°C)
    - Conversion of units: T(k) = T (°C)
    - Apparatus: Analogue thermometer, digital thermometer, temperature sensor/probe connected to a data logger.
  4. Volume
    - SI unit: Cubic metre (m3)
    - Other units: Cubic centimetre (cm3), cubic decimetre (dm3)
    - Conversion of units: 1m3 = 1000 dm3
    1 dm3 = 1000 cm3
    - Apparatus:
    - For LIQUIDS: measuring cylinder (measures volumes to the nearest 0.5 cm3), burette (measures volume to the nearest 0.05 cm3), and pipette (measures fixed volumes).
    - E.g. 10.0 cm3 / 25.0 cm3
    - For GASES: Gas syringe (measures volumes up to 100 cm3)
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3
Q

What happens before we read the volume of a liquid?

A
  • When a liquid is placed in a container, it forms a curve which is known as the meniscus. (Can be convex or concave)
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4
Q

What is a meniscus?

A
  • A meniscus is a curve that is formed when a liquid is placed in a container.
  • Most liquids like water have a concave meniscus that curves upwards at the edge.
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5
Q

What is a concave meniscus?

A
  • It curves upwards at the edges in most liquids.
  • Mercury has a convex meniscus which curves downwards at the edges.
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6
Q

What is a convex meniscus?

A
  • It curves downwards at the edges in substances such as mercury; a liquid containing metal.
  • The eye should be aligned to the meniscus when reading the volume of a liquid, which prevents parallax error.
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7
Q

What is a parallax error?

A
  • Parallax error is a type of error that is caused by viewing an object from different angles.
  • E.g. Reading off the bottom of a concave meniscus.
  • E.g. Reading off the top of a convex meniscus.
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8
Q

What are the factors that depend how we collect a gas as the end-product?

A
  • The method of collecting a gas depends on how soluble the gas is in the water, and how dense the gas is compared to air.
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9
Q

What are the methods of collecting a gas?

A
  1. Displacement of water:
    Properties of gas collected:
    - Insoluble in water (E.g. hydrogen)
    - Slightly soluble in water (E.g. oxygen, carbon dioxide)
  2. Downward delivery of gas:
    Properties of gas collected:
    - Soluble in water (E.g. chlorine)
    - Very soluble in water (E.g. hydrogen chloride, sulfur dioxide)
    - Denser than air.
  3. Upward delivery of gas:
    Properties of gas collected:
    - Very soluble
    - Less dense than air (E.g. Ammonia)
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10
Q

What can an inverted measuring cylinder be used to measure?

A
  • An inverted measuring cylinder that is filled with water can also be used to measure the volume of a gas through the displacement of water.
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11
Q

What is a gas syringe and what can it be used for?

A
  • A gas syringe can be used to collect a gas if the volume of the gas needs to be measured.
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12
Q

What are the methods of drying a gas?

A
  1. Drying agent:
    - Concentrated sulfuric acid
    Type of gas collected:
    - Most gases, including chlorine and hydrogen chloride
    - Excluding gases that react with sulfuric acid.
    - E.g. Ammonia
  2. Drying agent:
    - Quicklime (calcium oxide)
    Type of gas collected:
    - Ammonia
    - Excluding gases that react with quicklime. (E.g. Hydrogen chloride)
  3. Drying agent:
    - Fused calcium chloride
    Type of gas collected:
    - Hydrogen
    - Nitrogen
    - Carbon dioxide
    - Excluding gases that react with calcium chloride. (E.g. Ammonia)
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13
Q

What is a mixture?

A
  • A mixture is made up of 2 or more substances that are not chemically combined.
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14
Q

What is a pure substance?

A
  • A pure substance is made up of only one element of compound.
    **: During paper chromatography, the solvent is the compound and the dye is the element. (think it like that)
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15
Q

What is a substance with impurities?

A
  • A pure substance with impurities has a different chemical composition from the pure substance. (As it is ‘unpure’)
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16
Q

What are some methods of separating solid-liquid mixtures?

A
  1. Filtration
  2. Evaporation to dryness
  3. Crystallisation (using heat)
  4. Simple distillation
    - (e.g. Salt water can be separated into salt and water)
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17
Q

What is filtration?

A
  • Filtration can be used to separate an INSOLUBLE solid from a liquid
  • The insoluble solid is collected as the residue and the liquid is collected as the filtrate.
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18
Q

What is a residue?

A
  • A residue is the insoluble solid collected after filtration.
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19
Q

What is the filtrate?

A
  • A filtrate is the liquid collected after filtration.
20
Q

What is evaporation to dryness?

A
  • Evaporation to dryness is a process that can obtain a soluble solid (Can’t really see the solid, thus it is soluble because it tends to be invisible) from a solution by heating the solution until all the solvent boils off.
  • The solvent, which has a lower boiling point than the solute changes into a gas first. Thus, a solid is left behind.
  • This method is suitable for obtaining solids that do not decompose (Break down) on heating. (E.g. salt)
21
Q

What is crystallisation?

A
  • Crystallisation is a process that can be used to obtain soluble solid(s) from a solution by allowing a hot saturated solution to cool.
  • A saturated solution is a solution in which no more solute can be dissolved in the solvent.
  • This method is suitable for obtaining solids that decompose on heating. (E.g. Sugar)
  • Many crystals require a fixed amount of water in their crystal lattice.
    -This water is known as the water of crystallisation and if the water is driven off by evaporation to dryness, a powder instead of crystals will be obtained.
  • Thus, crystallisation is used to obtain crystals.
22
Q

What is a lattice?

A
  • A lattice is the arrangement of atoms, molecules, or ions of a crystal in thew form of a space lattice.
23
Q

What are the steps of crystallisation?

A
  1. Heat the solution until it is saturated.
  2. Leave the hot saturated solution to cool until crystallisation occurs.
  3. Filter to collect the crystals, wash the crystals with cold distilled water, and dry them between a few sheets of filter paper.
24
Q

What is simple distillation?

A
  • Simple distillation is a process that can be used to separate a solvent from a solute.
  • E.g. Water can be separated from salt using this method (simple distillation).
  • The solvent, which has a lower boiling point than the solute changes into a vapour first.
  • The solute remains in the distillation flask.
  • The vapour then reaches the top of the distillation flask and enters the condenser
  • The vapour cools in the condenser and condenses back into a liquid.
  • Once all the solvent has changed into a vapour, the solute is left in the distillation flask as the residue.
25
Q

What is a distillate?

A
  • A distillate is the liquid that is collected in the conical flask.
26
Q

What are some methods that involve the separation of solids from a solid mixture?

A
  1. Magnet method
  2. Sublimation
  3. Soluble solid and insoluble solid
27
Q

(Magnetic method to separate a solid from a solid mixture) What is a magnet and what is its function?

A
  • A magnet can be used to separate a magnetic solid from a non-magnetic solid.
  • Iron, cobalt, and nickel are magnetic metals.
  • Compounds of some metals are also magnetic.
  • E.g. Magnetite; It is a naturally occurring oxide of iron that is magnetic.
28
Q

What is sublimation?

A
  • Sublimation is a process that can be used to separate a substance that changes from a solid state to the gaseous state directly.
  • E.g. Ammonium chloride is a substance that undergoes sublimation.
29
Q

(Separating a soluble solid from an insoluble solid) How can a soluble solid be separated from an insoluble solid?

A
  • A soluble solid can be separated from an insoluble solid by dissolving the soluble solid in a suitable solvent and carrying out filtration.
  • The insoluble solid is collected as the residue.
  • The soluble solid is obtained from the filtrate by the evaporation to dryness or crystallisation method.
30
Q

What are some apparatuses that involve the separation of liquid from a liquid mixture?

A
  1. Separating funnel
  2. Immiscible liquids
31
Q

What is a separating funnel and what can it be used for?

A
  • A separating funnel can be used to separate 2 liquids that do not dissolve in each other.
  • E.g. Some examples of these liquids are immiscible liquids.
32
Q

What are immiscible liquids?

A
  • They are liquids that do not dissolve in each other, and they are separated by a separating funnel.
33
Q

What are the steps of using a separating funnel?

A
  1. Pour the mixture of 2 immiscible liquids into the separating funnel and wait until 2 layers are formed, and the less dense liquid will form a layer above the denser liquid.
  2. open the tap, allow the bottom layer to flow into a beaker, and close the tap when the bottom layer has flowed into the beaker completely.
  3. Place another beaker below the separating funnel and open the tap to allow the remaining layer in the funnel to flow into the beaker.
34
Q

What is fractional distillation?

A
  • Fractional distillation is used to separate miscible liquids with different boiling points.
  • When a mixture containing 2 miscible liquids is heated, both liquids change into vapours.
  • The vapour of the liquid with the higher boiling point condenses into a liquid in the fractioning column and flows back into the round-bottomed flask.
  • The vapour of the liquid with the lower boiling point reaches the top of the fractionating column and enters the condenser, and it then condenses into a liquid in the condenser (after a while).
  • The liquid with the lower boiling point is collected first in the conical flask as the distillate.
  • When all of the liquid with the over boiling point has distilled over into the beaker, the temperature in the fractioning column increases to reach the boiling point of the remaining liquid.
  • The liquid with the higher boiling point will then distil over and it/they can be collected separately.
35
Q

What happens during fractional distillation?

A
  • During fractional distillation, the thermometer measures the temperature of the vapour that enters the condenser.
  • It does not measure the temperature of the liquid in the round-bottomed flask, which may be affected by the heat source.
36
Q

What is chromatography?

A
  • Chromatography can be used to separate a mixture of substances that have different solubilities in a given solvent.
  • The substances to be separated are distributed between 2 phrases and one of them is stationary and does not move, while the other phase moves in a definite direction.
37
Q

What happens during PAPER chromatography?

A
  • During paper chromatography, the solvent moves up the stationary chromatography paper, thus carrying with it the substances to be separated.
  • The more soluble substances move more quickly with the solvent than the less soluble substances, thus the substances are separated, and the separation experiment is successful.
  • The chromatography paper with the separated substances.
38
Q

What is a chromatogram?

A
  • A chromatogram is the chromatography paper with the SEPARATD substances. (Mainly separated solutes)
39
Q

What are some methods that involve the separation of liquid from a liquid mixture?

A
  1. Fractional distillation
  2. Chromatography
40
Q

What is the retention factor?

A
  • The retention factor is the ratio between the distance travelled by a substance, and the distance travelled by the solvent is a CONSTANT. (Rf value of a substance)
  • Formula for finding the retention factor/ Rf value of a substance:
    Rf = distance travelled by the substance/distance travelled by the solvent.
41
Q

What happens when the distances travelled by the substances and the solvent increases?

A
  • the distances travelled by the substances and the solvent increase with the time given for the chromatogram to develop.
42
Q

Does the Rf (retention factor) value of a substance change or remains constant?

A
  • The Rf value of a substance does not change as long as the chromatogram is obtained under the same conditions.

(Spec question: Why must it be the same conditions, same solvent, and same temperature?)
Ans: This is because it allows the substances to be identified based on their solubility because there is only ONE CHANGED variable.

43
Q

How can colourless substances be made to appear as coloured spots?

A
  • Colourless substances can be made to appear as coloured spots on a chromatogram by spraying the chromatogram with a suitable locating agent.
44
Q

What is a locating agent?

A
  • A locating agent is a substance that is sprayed on the chromatogram to allow colourless substances to appear as coloured spots on a chromatogram.
45
Q

Why is it important to measure the purity of substances?

A
  • By measuring the purity of substances, helps to identify harmful impurities and ensures that produces such as food stuff and drugs meet their qualified standards.
    (e.g. Is it clean enough? Did it meet the hygiene standards for food products?)
46
Q

How can the purity of a substance be determined?

A
  1. Use of chromatography:
    - Pure substance will only give a single spot in the chromatogram.
    - Impurities will appear as multiple spots with different Rf (Retention factor) values on the chromatogram.
  2. Melting and boiling points of a substance:
    - A pure substance has constant and fixed melting and boiling points.
    - Impurities of the substance/Impurify the substance and then raise the boiling point of it.
    - The more impurities present, the lower the melting point of the substance and the higher its boiling point

Pure chemistry 🧫⚗️💉 (12 decks)

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