Ch 1 Experimental Chemistry

• Measurement of TIME (def)

  • SI unit?
  • Apparatus?

  -How long it takes to measure something

  • second (s)
  • Digital stopwatch (+/-0.01s), analogue stopwatch (+/-0.1s)
• Measurement of TEMPERATURE (def)

  • SI unit?
  • Apparatus?

  -How hot/cold something is

  • Kelvin(K) [K= Temperature in Celsius + 273]
  • Digital thermometer -> has a wide temp. range

  Mercury/Alcohol thermometer - alcohol-> -10 degree celsius to 110 degree celsius

  Temperature sensors connected to data loggers ->automatically collect data
• Measurement of LENGTH (def)

  • SI unit?
  • Apparatus?

  -Distance between 2 points

  • Metre (m) [1m=10decimeter=100cm=1000millimeter]
  • Metre rule (+/-0.1), measuring tapes (+/-0.1 to +/-0.5)
• Measurement of MASS (def)

  • SI unit?
  • Apparatus?

  -How much matter is present in substance

  • kilogram(kg) [1kg=1000g=1000 000mg] [1t=1000kg=1000 000g]
  • Electronic balance (+/-0.01), beam balance
• Measurement of VOLUME (def)

  • SI unit?
  • Apparatus?
  • Which is the most accurate apparatus?*

  -Amount of space something occupies

  • cubic metre (m^3) [1m^3 = 1000dm^3 =1000 000cm^3]
  • pipette -> accurate fixed volume => 20.0cm^3/25.0cm^3
  • volumetric flask -> accurate large fixed volume =>100cm^3/250cm^3
  • measuring cylinder-> range of volume to nearest 0.5cm^3 / 1 d.p
  • *burette-> range of volume to 2 decimal points to the nearest 0.05cm^3
  • beaker -> hold liquids
• How to avoid parallax error?

  -eyes positioned perpendicular to the meniscus to measure the volume of liquid
• What is used to measure volume of gas?

  -Gas syringe => up to 100cm^3
• What are the physical properties of gas used to determine method?

  -solubility -> how easily gas dissolves in water

  -density ->how dense gas is compared to surrounding air
• When is water displacement used to collect gas?

  -When gas is insoluble to slightly soluble -> water dissolves soluble gases

  -Gas density does not affect

  
• How should measuring the volume of gas look like in a diagram?


  *Label diagram with ruler

  *Readings on apparatus

  *Plunger should be close to wall -> gastight

  *Add stoppers if necessary ->gastight

  
• When is downward delivery used?

  -When gas is soluble (can be insoluble)

  -Denser than air (displaces air at the bottom)

  *Relative molecular mass of air is 30

  
• When is upward delivery used?

  -When gas is soluble (can be insoluble)

  -Less dense than air (displaces air at the top)

  *Relative molecular mass of air is 30

  
• *What is the method used when the drying agent is quickline? (calcium oxide)

  -Calcium oxide absorb moisture and carbon dioxide from air

  -> need to be freshly heated before use

  -> not suitable for gases reacting with calcium oxide

  *only method where ammonia is suitable

  
• *What is the method used when the drying agent is concertrated sulfuric acid? (-> most gases+chlorine, hydrochloride)

  -Method unsuitable for gases reacting with sulfuric acid (ammonia)

  
• *What is the method used when the drying agent is fused calcium chloride? (->hydorgen, nitrogen, Carbon dioxide)

  -calcium chloride readily absorbs moisture from air

  ->need to be freshly heated before use

  ->not suitable for gases reacting with calcium chloride

  
• Drying gases based on chemical reaction (neutralisation)
• What physical techniques should be used for: solid-solid mixtures?


  -magnetic attraction*

  -sieving

  -using suitable solvents

  -sublimation*
• What physical techniques should be used for: solid-liquid mixtures?


  -filtration

  -evaporation to dryness

  -crystalisation

  -simple distillation
• What physical techniques should be used for: liquid-liquid mixtures?


  -use of separating funnel*

  -chromatography

  -fractional distillation
• How can magnetic attraction be used to separate?

  magnet can separate magnetic solids from non-magnetic solids
• How can a sieve be used to separate?

  separate solids with different particle sizes
• How can suitable solvents be used to separate?

  separate solid-solid mixtures where only 1 of solids is soluble in solvent
• How can sublimation be used to separate?

  separate substance that changes from solid to gaseous state directly upon heating
• What are some common substances that undergo sublimation?

  -iodine

  -napthalene
• Describe sublimation

  -1 of the solids sublimes into gas when heated and moves away from mixture

  -Gas will change back into solid when there is a cool surface for gas to deposit on

  -resulting solid deposit ->sublimate

  -pure sublimate collected by scraping off surface
• How is filtration used to separate?

  -separate insoluble solids from liquids that have particles smaller than pores

  -liquid that passes through -> filtrate

  -solid that remains->residue
• How is evaporation to dryness used to separate?

  -separates dissolved solid from its solvent by heating mixture until all solvent has vaporised

  -soluble solid must not decompose*

  -substance with lower boiling point turns into gas first
• How is crystallisation used to separate?

  -obtain a pure solid from its saturated solution
• What is a saturated solution?

  -no more solute can be dissolved
• Describe the steps for crystallisation

  1. Gently heat solution until saturation in evaporation dish (so substance decomposes into simpler substances)
  2. Cool the solution gradually to form crystals (the slower the cooling rate, the bigger the crystals formed) (solubility increases with temperature -> cooling saturated solution results in crystallisation)
  3. Filtrate mixture to collect solid crystals as residue
  4. Wash crystals with a small volume of cold* distilled water (so crystals do not dissolve*) to remove impurities
  5. Dry crystals between pieces of filter paper
• How is simple distillation used to separate?

  -separates a pure solvent and solute from a solution with different boiling point

  -liquid that is vapourised is collected by condensation so both solute and solvent obtained
• Describe steps for simple distillation*

  1. Solution heated. Boiling chips added for smooth boiling

  • Vapour rises and enters condenser

  2. Water Vapour cools in condenser and condenses

  • Pure water collected -> distillate

  3. More water vaporises -> solution is more concentrated

  • solid residue remained in distillation flask
• Water enters bottom of condenser

  -> exposes hottest vapour to coldest water

  ->maximises heat transfer
• What is a miscible liquid?

  -form a homogeneous solution when mixed together
• What is a homogeneous mixture?

  -composition is uniform throughout mixture
• What is an immiscible liquid?

  -forms a heterogeneous mixture when put together
• How is a separating funnel used to separate?

  -separates immiscible liquids

  -heterogeneous mixture -> 2/more liquids left undisturbed -> separates into layers

  -least dense -> top phase

  -most dense -> bottom phase
• Describe how oil and water mixture can be separated using a separating funnel

  1. pour mixture into separating funnel
  2. allow mixture to settle and separate into 2 layers
  3. Drain bottom layer that has a higher density, which is water and collect it in a container
• How is chromatography used to separate?

  -separate a mixture of substances which have different solubilities in a given solvent
• What do chromatograms show?

  -shows separated substances on paper after chromatography