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13 Cards in this Set
- Front
- Back
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Both aldehydes and ketones contain what functional group?
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Carbonyl - double bond O
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Where is the carbonyl group located in both?
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Aldehydes - on the end or terminal carbon
Ketones - on a non terminal carbon(only if the ketone contains more than 4 carbons does the placement need to be specified) |
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Aldehydes and ketones with the same number of carbons are what?
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Structural isomers
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Preparation of an aldehyde - including reagents and special procedures to stop what occuring?
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Oxidation of a primary alcohol - usually using a weaker oxidising agent such as dichromate so it does not become oxidised further to a carboxylic acid. The aldehyde must be distilled off to stop it being further oxidised.
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What is the name of the apparatus used to make sure aldehydes are not further oxidised?
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A condenser is used to ensure the aldehydes are distilled to stop them becoming carboxylic acids.
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Equation for preparation of aldehydes
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Primary alcohol with catalyst of dichromate, = aldehyde (aq) + 2H+(aq) + 2e-
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Equation for preparation of ketones
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Secondary alcohol with acidified dichromate = ketone (aq) + 2H+(aq) + 2e-. Ketones cannot be oxidised further
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Aldehydes and Ketones are in what state at RT?
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Except for methanal, which is a gas, the other low mass ones are all colourless liquids at RT.
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Are Ketones and Aldehydes soluble in water?
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Yes, due to their ability to form hydrogen bonds with water, low mass aldehydes and ketones are soluble in water. Any ketone or aldehyde with more than 5 carbons is virtually insoluble.
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Reactions of aldehydes - Acidified dichromate or permanganate
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These oxidising agents oxidise not only alcohols (primary and secondary), but aldehydes as well. Aldehydes are oxidised to form carboxylic acids.
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Aldehyde reaction with Tollens Reagent
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Tollens reagent is a mild oxidising agent that will oxidise aldehydes but not alcohols or ketones. It must be warmed, and is the diammine silver complex ion, [Ag(NH3)2]+. The aldehyde is oxidised to a carboxylic acid, and the metallic silver either appears as a fine black ppt or as a 'silver mirror' on the inside of a clean test tube.
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Aldehyde reaction with Benedicts (Fehlings) solution
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Fehlings solution contains Cu2+ ions in complex form. They are a mild oxidising agent which can be reduced by aldehydes to form copper 1 oxide (Cu2O), which is a red brown ppt.
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Ketones - react or not?
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Ketones do not react with any of the reagents listed, and are only distinguishable from aldehydes by the fact that aldehydes do react.
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