chap 1 Flashcards
what is the si unit for time?
seconds
what apparatus can be used to measure time?
- digital stopwatch - to the nearest 0.01 second
- analogue stopwatch - to the nearest 0.1 second
what is the si unit for temperature?
kelvin (degree celsius temp + 273)
what is the si unit for length?
metre
what apparatus can be used to measure length?
- metre rule
- measuring tape
what is the si unit for volume?
cubic metre
what apparatus can be used to measure volume?
- measuring cylinder - to the nearest 0.5 cm3 (larger volume)
- pipette - to the nearest cm3 (for smaller volume)
- volumetric flask - to the nearest cm3
- burette - to the nearest 0.05 cm3
how to read the volume of a liquid?
we should position our eyes at the meniscus to prevent parallax error
what apparatus can be used to measure the volume of gases?
gas syringe
what physical properties should be considered when collecting gases ?
solubility and density
what are the methods to collect gas?
- water displacement - used for gases that are insoluble or slightly soluble in water, density does not affect gas collection
- downward delivery - used for gases that are dense than air, can be soluble or insoluble
- upward delivery - used for gases that are less dense than air, can be soluble or insoluble
what gases are insoluble or slightly soluble in water?
carbon dioxide, oxygen, hydrogen, nitrogen
what gases are less dense than air?
ammonia, hydrogen, nitrogen
define solubility
how easily the gas dissolves in water
what are the methods to dry gases?
- concentrated sulfuric acid - this method is suitable for acidic and neutral gases, not suitable for alkaline gases (e.g. ammonia) as they react with acid to form salt
- calcium oxide -must be freshly heated before use, suitable for alkaline and neutral gases (e.g. ammonia), not suitable for acidic gases as they react with calcium oxide to form salt
- fused calcium chloride - must be freshly heated before use, can be used for all gases except ammonia as it reacts with calcium chloride
what is magnetic attraction used for?
to separate magnetic solids from non-magnetic solids
what physical properties should be considered when choosing separation techniques?
particle size, solubility, melting and boiling point
what is sieving used for?
to separate solids with different particle sizes
what is a solvent?
the liquid that dissolves solids
what is the solute?
the solid that dissolves in the solvent
what is using suitable solvents used for?
a suitable solvent can be used to separate solid-solid mixtures in which only one solid is soluble in the solvent
what is sublimation used for?
sublimation can be used to separate a substance that changes from the solid to gaseous state directly. sublimation can be used to separate a mixture of solids where one sublimes on heating while the others are stable at the sublimation temperature
what substances can undergo sublimation?
dry ice (carbon dioxide), naphthalene (mothballs), ammonium chloride and iodine
how does sublimation take place?
the solid sublimes into a gas on heating and moves away from the mixture. by providing a cool surface for the gas to deposit on, the gas will change state back into a solid. the resulting solid deposit, known as the sublimate, can be collected by scraping them off the cool surface
what is filtration used for?
filtration can be used to separate insoluble solids from liquids
what is a filtrate?
the liquid that passes through the filter paper
what is the residue?
the solid that remains on the filter paper
what is evaporation to dryness used for?
it is used to separate a dissolved solid from its solvent by heating the solution until all the solvent has vaporised. it works base on the difference in boiling point between solute and solvent
how does evaporation to dryness take place?
heat the solution in an evaporating dish until all the solvent evaporates and only the solid is left
what is crystallisation used for?
if a solute decomposes or breaks down into simpler substances when heated, crystallisation is used. crystallisation is used to obtain a pure solid from its saturated solution. a saturated solution is one in which no more solute can be dissolved in the solvent
how does crystallisation take place? (copper (ll) sulfate)
- gently heat the copper (ll) sulfate solution in an evaporating dish to evaporate most of the liquid until a saturated solution is obtained. stop heating before all the solvent has evaporated
- cool the solution gradually until the coper (ll) sulfate crystals appear within the solution
- carefully pour the mixture through a filter funnel lined with filter paper to filter and collect the solid crystals
- wash copper (ll) sulfate crystals with cold distilled water to remove any impurities and dry the crystals between pieces of filter paper
what is simple distillation used for?
to separate a pure solvent from a solution
how does simple distillation take place? (seawater)
- the salt water is heated. boiling chips are added for smooth boiling. at 100 degree celsius, the water boils. the vapour rises and enters the condenser through the exit sidearm of the distillation flask.
- the water vapour cools in the condenser and condenses back to liquid water. pure water is collected in the conical flask as the distillate.
- as more water vaporises, the salt solution becomes more concentrated. eventually, a solid residue of salt remains in the distillation flask
what are miscible liquids?
liquids which form a homogeneous solution when mixed
what are immiscible liquids?
liquids which form a heterogeneous mixture when mixed. when immiscible liquids are left undisturbed, they can separate into layers known as phases
what is a separating funnel used for?
a separating funnel is used to separate immiscible liquids.
what is chromatography used for?
used to separate a mixture of substances which have different solubilities in a given solvent
why cant ink be used to mark the start line for chromatography?
ink will dissolve and interfere with the results obtained
what is the rf value?
rf value = distance travelled by the substance / distance travelled by the solvent
what does rf value show?
the rf value of a substance is constant if the chromatography is carried out under the same conditions (same temperature and same solvent). using rf values allows us to compare chromatograms which have been run for different durations using the same solvent and temperature
what is an application of chromatography?
detect small quantities of banned substances in an athlete’s urine or blood sample
what is fractional distillation used for?
used to separate miscible liquids with different boiling points
what is the difference between fractional distillation and simple distillation?
a fractionating column is added to the simple distillation set-up.
how does fractional distillation take place? (ethanol and water)
- as the solution is heated, both ethanol and water vapour rise up the column
- water has a higher boiling point than ethanol. the water vapour condenses on the cool surfaces within the fractionating column and the water returns to the flask
- ethanol vapour continues to rise. at its boiling point of 78 degree celsius, it exits the column through the sidearm at the top
- the hot ethanol vapour cools and condenses into a liquid as it travels through the inner tube of the condenser.
- liquid ethanol (distillate) flows into the conical flask.
what are the properties of the fractionating column?
- the fractionating column contains glass beads or other small solid objects which provide a larger surface area for the vapours to condense on
- the length of the fractionating column determines its ability to separate substances
- liquids with similar boiling points will require a longer fractionating column for better separation
what is and application of fractional distillation?
ethanol produced by glucose fermentation is extracted in breweries
how can purity be determined?
- using chromatography - a pure substance should show only one spot / component on the chromatogram. an impure substance or mixture would show more than one spot
- using melting / boiling point - a pure substance has a fixed melting and / or boiling point while mixtures melt or boil over a range of temperatures
what are the impacts of impurities on melting and boiling point?
- the greater the amount of purities, the larger the change in melting or boiling points
- impurities will increase the boiling point
- impurities will decrease the melting point
how to use a separating funnel ?
when a heterogeneous mixture is left to settle into separate layers, each component can be removed by opening the tap at the bottom and collecting it in separate flasks or beakers
