Wednesday 4 June 2008

IS notes unit 10,11 form 2

1) Acids (acidic substances) taste sour, fruits contain citric acid and soft drinks contain carbonic acid. Alkalis (Alkaline substances) are slippery. 2) Some natural materials contain pigments that changes colour in acid / alkalis, they are natural indicators. 3) Common acids in Lab.: hydrochloric acid, sulphuric acid and nitric acid. 4) Common alkalis in Lab.: sodium hydroxide and ammonia. 5) Litmus: Acids turn blue litmus blue and alkalis turn red litmus blue, if no change for both colour, it’s neutral. (Litmus solution or litmus paper which soaked in the litmus solution.) 6) Universal indicator: they show a wide range of colours depending on the degree of acidity or alkalinity of substances, pH paper is soaked in the universal indicator. pH scale shows the different colour to show their acidity or alkalinity from 0 to 14. Lower value is more acidic and higher value is more alkaline, 7 is neutral. 7) pH meter is as electronic appliance that measure the value accurately. 8) The pH value in daily: blood: 7.4; stomach juice:2; intestinal juice: 8.5, skin: 5.5 and soil: 6-8. 9) Test for hydrogen: burning splint, burn with a pop sound (explosion). 10) Corrosive effect of metal + acid => Hydrogen + salt , (energy release) Acids corrode metals but aluminium resistance from this because aluminium react with oxygen and form aluminium oxide which resistance from corroding. 11) Corrosive effect :acid +marble (-> Calcium carbonate)=> Carbon dioxide+ water (+ salt) 12) Rain water is slightly acidic because in air dissolves in rain water and form carbonic acid, when the pH value of rain water lower than 5.6, it’s acid rain. They formed because air pollutants such as sulphur dioxide and nitrogen oxides. 13) The acid rain will corroding stone(marble) structures, metal structures, damage forests and make the water be acidic where most aquatic life can’t live. It’s a regional problem that HKSARgov. and Guangdong Provincial gov. joined to control acid rain. They reduce the release pollutants form vehicles and power stations. We can use energy efficiently to reduce also. 14) Acids help to preserve food, they slow down their activities or even kill them. Vinegar is non-toxic solution that contains acetic(ethanoic) acid so they use vinegar as food preservative. 15) *higher pH value can slow down the browning effect. 16) Oven, drain cleanser contains sodium hydroxide, glass cleanser contains ammonia and toilet cleanser contains hydrochloric acid. 17) Neutralization: Acids + Alkalis => Salt + water 18) Daily use of neutralization: Antacid (alkaline) is used for excess acid in stomach, Baking soda for bee, ant and mosquito stings and vinegar for wasp stings, lime is alkali that neutralize the acidic soil. All chemical waste should be neutralize before dispose it. Also, lye is added to neutralize the acidity of glutinous rice and vinegar is used to neutralize the lye in noodles. 19) Strong acids or alkalis cause a burn, they are highly corrosive. When diluting a concentrated solution, we add it to water but not add water to solutions, adding them slowly and mix them when diluting. 20) We detect different stimuli (stimulus) with different sense organs, they sense with their own sensory cells. Eye→sight, ear→hearing, tongue→taste, nose→smell, skin→touch. 21) The parts of eye: Eyebrow, eyelash on the eye lid; Cornea is a clear layer in front of eye, help focusing light, Iris, changes the size to fit the amount of light going in, they have different colours refer to pigments; Pupil allows light go in the eye; focusing muscles help control the thickness of lens to focus image; Lens can change in thickness to focus light in retina; Retina contains light-sensitive cell and sends stimuli to brain by Optic nerve; Blind spot is in front of the optic nerve and we can’t sense light there, yellow spot is that most of the light-sensitive cell are there, protective coat (sclera) protects eyeball and maintain its’ shape. Aqueous Humor(watery fluid) is water in front of lens and Vitreous Humor is jelly-like fluid that behind lens. The light goes with an inverted image in the eye. 22) Cones cells sense colours in bright light, three types sensing for red, blue and green. They used to form colour images (no. 6M), rod cell form B&W images in dim light, 1 types only (no. 1.2 B) 23) Three reason for short sight: the lens stable to be thick, eyeball too long or focusing muscles too weak, three reason for long sight just the opposite.

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