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GCSE6 Analysis
AQA GCSE chapter 12 chemical analysis
| Question | Answer |
|---|---|
| Describe how to carry out a chromatography experiment | draw a start line in PENCIL, ABOVE the water level; place a dot of your mixture and a dot for references on start line; place the paper in beaker WITH A LID; remove paper before the solvent reaches the top of the paper; draw a line on the solvent FRONT |
| Why does the start line need to be drawn in PENCIL? | if the line was drawn in ink, the ink could rise with the solvent as well as your mixture |
| Why does the start line need to be drawn ABOVE the water level? | If the line was below, the dot from the mixture would dissolve into the water instead of rising up the paper |
| Why do we place a lid on top of the beaker? | to prevent teh solvent from evaporating |
| Looking at a chromatogram, how would you know if a chemical is a mixture? | There would be more than one dot above the start line |
| Looking at a chromatogram, how would you know if HOW MANY different chemicals were in a mixture? | COUNT the dots above the start line |
| Looking at a chromatogram, how would you know if how many different chemicals were in a mixture? | COMPARE the HEIGHT of the dots above the start line of the mixture to the HEIGHT of reference/pure chemicals; if two dots are at the same height, then they are the same chemical |
| Looking at a chromatogram, how would you know which chemical is the most soluble? | the most soluble chemical rises the furthest; has the biggest Rf |
| Explain why a chemical rise up the paper | A chemical rises up the paper when it forms STRONGER bond with the mobile phase (solvent) than the bond it forms with the stationary phase (paper) |
| What is the stationary phase? | the paper |
| What is the mobile phase? | the solvent |
| How do you work out the Rf for a given dot? | measure the distance from the start line to the MIDDLE of the dot; measure the distance from the start line to the solvent front; divide the start-to-dot by start-to-front |
| Looking at a chromatogram, how would you know if how many different chemicals were in a mixture? | COMPARE the Rf of the dots above the start line of the mixture to the Rf of reference/pure chemicals; if two dots are at the same Rf, then they are the same chemical |
| What is the chemical test for oxygen gas? | A GLOWING splint RELIGHTS |
| What is the chemical test for hydrogen gas? | A LIT splint makes a SQUEAKY pop |
| What is the chemical test for carbon dioxide gas? | when BUBBLED through LIMEWATER, the limewater turns cloudy |
| (CHALLENGE) why is it not enough to identify carbon dioxide gas to say “carbon dioxide turns off a flame”? | Because nitrogen gas also turns off a flame |
| What is the chemical test for Al+3? | a white precipitate forms with sodium hydroxide; the precipitate WILL dissolve if more Sodium Hydroxide is added |
| What are the 2 chemical tests for Ca+2? | a white precipitate forms with sodium hydroxide; the precipitate WILL NOT dissolve if more Sodium Hydroxide is added |
| What are the 2 chemical tests for Cu+2? | A blue precipitate forms with sodium hydroxide; also green flame |
| What is the chemical test for Fe+2? | A green precipitate forms with sodium hydroxide solution |
| What is the chemical test for Fe+3? | A brown precipitate forms with sodium hydroxide solution |
| What is the chemical test for NH4+? | A white precipitate forms with sodium hydroxide solution; if the precipitate is heated, a pungent gas that turns red litmus paper to blue is given off; the gas is Ammonia |
| What is the chemical test for Cl-? | A white precipitate forms with silver nitrate and acid solution |
| What is the chemical test for Br-? | A cream precipitate forms with silver nitrate and acid solution |
| What is the chemical test for I-? | A yellow precipitate forms with silver nitrate and acid solution |
| Describe a simple chemical test to distinguish between Cl- and I- ions? | Add acid and then silver nitrate solution; a white precipitate indicates Cl- ions and a yellow precipitate indicates I- ions |
| Describe a simple chemical test to distinguish between Fe+2 and Fe+3 ions? | Add Sodium Hydroxide; if the precipitate that forms is green, then the ion is Fe+2; if the precipitate is brown, then Fe+3 |
| What is the colour of the flame when you burn Na+ ions? | Yellow |
| What is the colour of the flame when you burn Ca+2 ions? | brick red (orange-red) |
| What is the colour of the flame when you burn Cu+2 ions? | Green |
| What is the colour of the flame when you burn K+ ions? | Lilac |
| What is the colour of the flame when you burn Li+ ions? | Crimson |
| What is the chemical test for CO3-2? | Fizz on addition of HCl; the gas will turn limewater cloudy |
| What is the chemical test for SO4-2? | A white precipitates forms on addition of dil HCl and BaCl2(aq) |
| A sample of water produces a green precipitate on addition of Sodium Hydroxide and fizzes on addition of acid. What ions are present in solution? | Fe+3 and CO3 -2 |
| Give two applications to flame tests and chemicals tests | Blood tests and testing for water |
| A sample of water produces a blue precipitate on addition of Sodium Hydroxide and a cream precipitate on addition of Nitric acid + silver nitrate. What ions are present in solution? | Copper Cu+2 and Bromide Br-1 ions |
| (HIGHER) What is the IONIC equation for the precipitation of copper hydroxide? | Place the ions as reactants: Cu+2 + OH- --> ....; Work out formula of copper hydroxide: Cu(OH)2; The copper hydroxide is the product, after the arrow; Cu+2 + OH- --> Cu(OH)2; Balance: Cu+2 + 2 OH- --> Cu(OH)2 |
| (HIGHER) What is the IONIC equation for the precipitation of silver bromide? | Place the ions as reactants: Ag+ + Cl- ...; Work out formula of silver bromide: AgBr; The silver bromide is the product, after the arrow: Ag+ + Cl- AgBr; check Balancing |
| (HIGHER) What is the IONIC equation for the reaction between Sodium Hydroxide and copper ions? | Always look for spectator ions: classical spectators are sodium, potassium and nitrate ions. Then write the ionic equation as usual. |
| (HIGHER) What is the IONIC equation for the reaction between Sodium Hydroxide and copper sulfate? | WORD : Sodium Hydroxide(aq) + Copper Sulfate(aq) --> Sodium Sulfate(aq)+Copper Hydroxide(s); CHECK FORMULAE NaOH + Cu(SO4) -> Cu(OH)2 + Na2(SO4); BALANCE 2NaOH + Cu(SO4) -> Cu(OH)2 + Na2(SO4); remove ions that stay (aq): 2OH(aq) + Cu(aq) -> Cu(OH)2(s) |
| (HIGHER) What is the IONIC equation for the reaction between Silver Nitrate and Sodium Chloride? | WORD : Silver Nitrate+Sodium Chloride --> Sodium Chloride(aq) + Silver Chloride(s); CHECK FORMULAE Ag(NO3)(aq) + NaCl (aq)->AgCl(aq) + Na(NO3)(aq); remove ions that stay (aq) AND CHECK CHARGES: Ag+(aq) + Cl-(aq) --> AgCl(s) |
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ursulinechem2
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