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chemistry group 2 questions

1) A marble chip is placed in a test tube. a 1cm depth of 1mole do^-3 H2SO4 is added to the test tube containing the marble chip. a gas is evolved but the bubbles stop after a few seconds.
carbon dioxide gas is produced initially. suggest why this quickly stops being evolved from the surface of the marble chip.

2) water is put in a testtube to depth of aboput 1cm. a very small amount of solid calcuim hydroxide is added to the water./ not all the calcium hydroxide dissolves. three drops of universal indicator solution are added to the mixture. the indicator turns blue. drops of 2 mol dm^-3 HCL are added to the mixutre. the test tube is shaked after each drop has been added. the universal indicator turns red and then turns blue when the tube is shaken.

Explain in terms of acid-base behavious why the indicator changed colour in this way.

3) a wooden splint which has been soaked in barium nitrate solution is put into the bunsen burner flame. the flame tinged with a green colour.
the green light emitted by the heated barium nitrate is analyed using an atomic emission spectrometer. describe the appearance of the spectrum produced.



thanks.
1 CaSO4 formed at surface is insoluble so blocks further reaction
2.Ca(OH)2 porly soluble, so initial blue colour due to some OH- ions realeased in solution. Drop of acid gives small amount of acid in XS, but quickly neutralised. Then the Ca(OH)2 that was solid disolves and so it releases OH- again turning it blue
Line spectra produced with lines of emmission at a specific green wavelength. The electrons in the Ba2+ are excited to a higher energy level. Energy is quantised so when the e- fall back to their ground state they emit a photon of light energy eqaul to the energy gap they fall, such that delta E (energy gap) = h x frequency, in this case, apple green light

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