chem notes o level

Chapter 1: Experimental Chemistry

How are physical quantities measured? Time -SI unit: s (seconds) -60 seconds = 1 minute -Measured with stopwatch Temperature -SI unit: K (kelvin) -Temperature in kelvin = Temperature in celsius + 273 -Measured with thermometer Length -SI unit: m (metre) -1 kilometre = 1000 metres -Measured with measuring tape, ruler Mass -SI unit: kg (kilogram) -1 kilogram = 1000 grams -Measured with beam, electronic balance Volume -SI unit: m^3 (cubic metre) -1 cubic metre = 100 millilitres -Measured with pipette (accurate fixed volume up to around 25 cm^3), volumetric flask (big volume up to around 250 cm^3), measuring cylinder (1 d.p. around 20-50 cm^3), burette (2 d.p. 50 cm^3) -Volume of gases are measured with a gas syringe Solubility of gases -Gases can dissolve in water -Insoluble gases: H2, N2, CH4 -Slightly soluble gases: O2 and CO2 -Very soluble gases: SO2, Cl2, NH3 How are gases collected? Water displacement -Gas is bubbled through water and collected in a gas jar -The gas can only be insoluble or slightly soluble in water -Density does not affect this method, but note that density of water is 1 g/cm^3 -e.g. hydrogen, oxygen, carbon dioxide

Downward delivery -Gas is collected in a gas jar and sinks down if denser than air -Solubility in water does not affect this method -Must be denser than air -The Mr of air is 29 -e.g. chlorine, hydrogen chloride, sulfur dioxide Upward delivery -Gas is collected in a gas jar and floats up if less dense than air -Solubility in water does not affect this method -Must be less dense than air -The Mr of air is 29 -e.g. ammonia

Calculating the density of gases -Relative atomic mass (Ar): number of protons and neutrons in an atom -The relative atomic mass of air is around 29 -Relative molecular mass (Mr): number of protons and neutrons of all atoms in a molecule -Density = mass / volume Methods for drying gases Concentrated sulfuric acid -Most gases can be dried -Gases which react with sulfuric acid cannot be used -The moist gas must be bubbled through the sulfuric acid Quicklime (calcium oxide) -Most basic and neutral gases can be used, such as ammonia -Gases which react to calcium oxide cannot be used -The gas must be passed through the calcium oxide -Calcium oxide readily absorbs moisture from the air, so it must be freshly heated before use Fused calcium chloride (fused means dried) -Hydrogen, nitrogen, carbon dioxide is regularly used -Gases which react with calcium chloride cannot be used -The gas must be passed through the calcium chloride -Calcium chloride readily absorbs moisture from the air, so it must be freshly heated before use How are substances in mixtures separated? What is a mixture? -A mixture consists of two or more substances that are not chemically combined -The physical properties of a substance determines the separation techniques used

Seperating solid-solid mixtures Using m