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A graduated beaker measures approximate volume of a liquid. A pipette measures fixed volumes very beaker volumetric flask measuring 3 cylinder accurately. Pipettes of volumes 10 cm , 20 cm3 and 25 cm3 are used in laboratory. For accurate measurement of the volume of a liquid, a measuring cylinder is used. For more accurate measurement, a burette is used which can measure the volume of a liquid correct to 0. Volumetric flasks are used to measure fixed volumes of liquids. Volumetric flasks of cm3, cm3, cm3 and 1 dm3 are available in the laboratory.
Volumetric flasks are also used for preparing solutions of known concentrations.
How to Read the Volume of a liquid? This curved surface is called meniscus. If the meniscus is concave, read off the scale at the bottom of the meniscus. If the meniscus is convex, read off concave convex the scale at the top of the meniscus.
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For this purpose gas syringes are used. Displacement of water ii. Downward Delivery or Upward Displacement of Air iii. Upward Delivery or Downward Displacement of Air Displacement of water - This method is suitable for collecting gas gas collected gases that are insoluble or slightly soluble in water such as carbon dioxide CO2 , hydrogen H2 and oxygen O2. In this method, the gas is passed through water into an upside down jar full of water; water the gas starts collecting on the top while the water gets displaced downwards. In this method, the gas is introduced in a gas jar.
Being heavier it starts settling at the bottom and leaving the air to escape from the mouth of the jar. In this method, the gas is introduced into an upside down gas jar. Being lighter than air, the gas starts rising at the top and leaves the air to escape from the bottom end of the jar. This method is also called downward displacement of air. Unit 1 13 Experimental Design - The table given as below shows the solubility and density of some common gases. Gas Solubility in Water Density hydrogen insoluble less denser oxygen slightly soluble slightly denser chlorine soluble denser carbon dioxide slightly soluble denser ammonia extremely soluble less denser hydrogen chloride very soluble denser table 1.
In order to collect a dry sample of a gas, it should be passed through a drying agent.
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Using Conc. Sulfuric Acid H2SO4 - To dry a gas with concentrated sulfuric acid, a double moist gas dry gas in out neck bottle or a conical flask with two delivery tubes see fig. The tube introducing the gas should be immersed in the acid while the exiting tube should remain out of the acid. It cannot be used for ammonia NH3 which is alkaline and leads to a chemical reaction. Purity of a Substance - A pure solid has a fixed and exact melting point.
While choosing a suitable technique, one should take into account the properties of each substance present in the mixture. Term Meaning mixture an impure substance containing two or more substances that are not chemically combined impurities unwanted materials present in a given substance suspension a mixture in which insoluble solid particles are suspended in a liquid precipitate an insoluble solid substance formed in a solution as the result of a chemical reaction filter or filter medium the porous material through which only liquids and dissolved substances can pass through but solids or suspended particles are left behind.
Filter paper, closely packed glass fibres, cotton, woven wire, cloth, sand etc. Decanting - Decanting is used to separate insoluble solids from a liquid by carefully pouring the liquid away. For example, a mixture of sand and salt can be separated by filtration using water sand residue as solvent. This phenomenon is called sublimation. Unit 1. For example, when a mixture of iodine and solidified iodine sand is heated, iodine sublimes i. When these vapour touch a cold surface, wet cloth to cool they solidify again and are thus separated from sand.
For example, sugar decomposes to water and carbon when its solution is heated strongly.
Similarly, strong heat may release water of crystallization from crystals and leave them in powder form. Another drawback of using this method is that soluble impurities present in the solution may contaminate the solid to be recovered. For such substances, crystalization is a better technique. Desalination optional water out - Desalination is a process of removing salt from sea applied pressure water by distillation or by reverse osmosis.
An external pressure forces the water to salty water pure water pass through the semipermeable membrane but leaves behind the dissolved salts. Now allow this solution to cool to room temperature. This makes the dissolved solid to reappear as pure crystals. Simple Distillation - Simple distillation is used to separate a pure liquid solvent from its solution by heating the mixture upto its boiling point and then condensing the vapour.
Heat the solution in a distillation flask. The vapour rises and enters the condenser where they are cooled thermometer and change back to liquid. Pure liquid is collected as distillate in the flask. The salt solution in the distillation flask becomes more and more concentrated as distillation proceeds.