Acids & Bases, Reproduction in Plants
Main points for Acids & Bases:
Acids
Substance which produces hydrogen ions as the only positive ions when dissolved in waterProperties of acids:
- Sour taste
- change colour of indicators (e.g. turn blue litmus paper red)
- contain hydrogen ions and can conduct electricity
- react with metals, carbonates and base
Acids can be strong or weak.
Strong acids:
- hydrochloric acid (HCl)
- nitric acid (HNO3)
- sulfuric acid (H2SO4)
Weak acids:
- acetic acid (found in vinegar)
- citric acid (found in lemons)
- tartaric acid (found in grapes)
Reaction with metals
Acids react with metals to produce salt and hydrogen
Acid + metal ---> salt + hydrogen
Observations
- effervescence observed, colourless, odourless gas evolved whihc extinguishes a lighted wooden splint with a "pop" sound
- grey solid reduced in size (when in excess), dissolves to form colourless solution
- heat liberated
Reactions with carbonates
Acids react with carbonates to produce salt, carbon dioxide and water
acid + carbonate ---> salt + carbon dioxide + water
Observations
- effervescence occurs
- colourless, odourless gas evolved which reacts with calcium hydroxide to form a white precipitate
- white solid dissolves to form a colourless solution
Reactions with bases
Acids react with bases (metal oxides and metal hydroxides) to produce salt and water
acid + base ---> salt + water
Observations
- white solid dissolves to form a colourless solution
- heat is evolved, no visible change
Bases & Alkalis
Bases have a bitter taste and feel slippery or soapy to touch
Some bases are very corrosive, like caustic soda
Bases that can be dissolved in water are called alkalis
Bases are oxides or hydroxides of metal that react with an acid to form a salt and water only. Most bases are insoluble in water.
An alkali is a metal hydroxide which is soluble in water and produces hydroxide ions (OH-) in water.
Types of Oxides
- Acidic oxide
- non-metallic oxide that neutralises a base to form salt and water only, reacts with water slightly to form an acid solution
- Basic oxide
- metallic oxide that neutralises an acid to form salt and water only, forms an alkali if soluble in water
- Neutral oxide
- non-metallic oxide that shows neither acidic nor basic properties, insoluble in water and do not react with water
- Amphoteric oxide
- metallic oxide that reacts with both acid and base to form salt and water, has both acidic and basic properties
Strong alkalis ionise completely in water to produce hydroxide ions and there are no molecules left. Weak alkalis ionise incompletely in water to produce few hydroxide ions and most alkali molecules remain as molecules.
Properties of bases
- Alkalis have a soapy feel and a bitter to taste
- Alkalis can change the colour of indicators (e.g. turn red litmus paper blue)
- Bases can react with acids to form salt and water only, through a process called neutralisation, where acid properties are destroyed
- Bases can react with ammonium salts to form salt, ammonia and water
base + ammonium salt ---> salt + ammonia +water
Observations
- colourless, pungent gas is evolved
- the gas turns damp red litmus paper blue
Main points for Reproduction in Plants
Parts of a flower
General
- petals - usually bright coloured to attract pollinators
- sepals - protects to flower at bud stage
- epicalyx - occurs in certain plants only, forms a layer outside the petals
- receptacle - enlarged end of stalk, holds other parts of flower in place
- pedicel (stalk) - attaches flower to plant
Pistil (female)
- ovary - contains one or more ovules
- style - stalk that connects stigma to ovary, holds stigma in optimal position for pollination
- stigma - site of pollination
Stamen (male)
- anther - produces pollen grains
- filament - holds anther in optimal position to release pollen
Pollination
transfer of pollen grains from the anther to the stigma
Self-pollination: transfer of pollen grains to the stigma of the same flower or a different flower on the same plant
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