Chemistry - 9202 OxfordAQA

Identification Of Common Gases C

Gbogbo ọrọ náà

Five stoppered test tubes sit on the bench and not one of them carries a label. Four hold gases you cannot see at all; the fifth has a faint green tint if you catch it against white paper. There is no instrument in the room that will read them out for you. What you do have is a wooden splint, two strips of coloured paper, a bottle of cloudy-looking water and your own sense of smell used very carefully. Within about four minutes, every tube can be named.

That is the quiet promise of qualitative analysis: a handful of cheap, repeatable observations, each one designed so that a single gas gives a result nothing else gives. This lesson works through the five gases OxfordAQA expects you to identify, shows the reaction behind each observation rather than asking you to memorise a list, and deals with the two details that quietly cost marks every year: why the paper has to be damp, and why a limewater test left running too long can tell you the opposite of the truth.

Ebumnobi

  1. A pop is heard when a lighted splint is placed near hydrogen gas.
  2. A glowing splint relights in a test tube of oxygen gas.
  3. Carbon dioxide turns limewater (calcium hydroxide solution) cloudy white.
  4. Ammonia has a characteristic sharp, choking smell. It also makes damp red litmus paper turn blue. Ammonia forms a white smoke of ammonium chloride when hydrogen chloride gas, from concentrated hydrochloric acid, is held near it.
  5. Chlorine has a characteristic sharp, choking smell. It also makes damp blue litmus paper turn red, and then bleaches it white.

Maapụ uche

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Akwụkwọ Ọmụmụ

Most of the chemistry in this course predicts what will happen. This part of it does the reverse. Something has already happened, a gas has come off a reaction mixture, and your job is to work backwards from what you can observe to what the gas must be. Chemists call this qualitative analysis: not how much, just what.

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Nnyocha Ọmụmụ

Ekele diri gi maka imecha ihe karịrị na Identification Of Common Gases C. Ugbu a na ị na-enyochakwa isi echiche na echiche ndị dị mkpa, ọ bụ oge iji nwalee ihe ị ma. Ngwa a na-enye ụdị ajụjụ ọmụmụ dị iche iche emebere iji kwado nghọta gị wee nyere gị aka ịmata otú ị ghọtara ihe ndị a kụziri.

Ị ga-ahụ ngwakọta nke ụdị ajụjụ dị iche iche, gụnyere ajụjụ chọrọ ịhọrọ otu n’ime ọtụtụ azịza, ajụjụ chọrọ mkpirisi azịza, na ajụjụ ede ede. A na-arụpụta ajụjụ ọ bụla nke ọma iji nwalee akụkụ dị iche iche nke ihe ọmụma gị na nkà nke ịtụgharị uche.

Jiri akụkụ a nke nyocha ka ohere iji kụziere ihe ị matara banyere isiokwu ahụ ma chọpụta ebe ọ bụla ị nwere ike ịchọ ọmụmụ ihe ọzọ. Ekwela ka nsogbu ọ bụla ị na-eche ihu mee ka ị daa mba; kama, lee ha anya dị ka ohere maka ịzụlite onwe gị na imeziwanye.

  1. Which gas relights a glowing splint? A. hydrogen B. oxygen C. carbon dioxide D. ammonia Answer: B
  2. A colourless gas is bubbled through limewater and the limewater turns cloudy white. The gas is: A. chlorine B. hydrogen C. carbon dioxide D. oxygen Answer: C
  3. Damp blue litmus paper is held in a tube of gas. The paper turns red and is then bleached white. Which gas is in the tube? A. ammonia B. chlorine C. hydrogen D. carbon dioxide Answer: B
  4. Why must the litmus paper be damp when testing for ammonia? A. Damp paper is easier to hold in the tube. B. The water cools the gas so that it reacts more slowly. C. The ammonia must dissolve in the water to produce hydroxide ions. D. The water reacts with the ammonia to produce ammonium chloride. Answer: C
  5. Ammonia gas meets hydrogen chloride gas from concentrated hydrochloric acid. What is the white smoke that forms? A. ammonium chloride B. calcium carbonate C. chlorine water D. ammonium hydroxide Answer: A

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