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About weiming1998

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  • Birthday 12/03/1998

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  • Location
    Western Australia
  • Interests
    Chemistry (sciences in general), reading, fishing and a game of chess or two.
  • College Major/Degree
    No degree yet, although I hope to get one some day.
  • Favorite Area of Science
  • Biography
    I am just a high school student interested in chemistry, and do chemistry experiments at home.
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  1. Although HF is a weak acid in aqueous solution, as it becomes more and more concentrated (approaching 100% hydrogen fluoride) , it becomes a lot more acidic, dissociating into H+ and HF2- ions instead, and doing so far more readily than when it is diluted in water. This could mean that it can donate a proton to the H2SO4, forming the H3SO4+ ion and the stable HF2- ion. Read this (http://en.wikipedia.org/wiki/Hydrofluoric_acid).
  2. There are several ways you can concentrate 3% H2O2. One way is by freezing it. Since H2O2 has a lower freezing point than water, it will stay liquid while all the water freezes. It is possible to get the H2O2 to at least 15% with freezing. With fractional crystallisation, a 60% concentrated solution could be made, but this would be difficult to set up. Another way is by evaporation/boiling. For your purposes, you do not need to fear about combustible vapours (H2O2 vapours are only significantly dangerous/explosive if your H2O2 is above 70% in concentration), but cranking the heat all the way
  3. Because an alcohol, after all, is just any molecule with an OH group. The rest of the molecule could be anything from just a simple saturated chain of carbon and hydrogen to ring/rings made of carbon and hydrogen to branching structures containing both rings, carbon hydrogen chains, double/triple bonds, and other functional groups. It is like the difference between a frog and an elephant. They both have four legs, but they are drastically different in most other aspects, and thus doesn't even look remotely similar.
  4. Add a couple of ml of the unknown acid that you're testing to a dilute solution of potassium permanganate or dichromate. If it is sulfurous acid, the bright orange/purple colour will change. If it is sulfuric acid, the colour won't change. Carefully smell the acid. Sulfuric acid hardly has a smell at room temperature, while sulfurous acid (which is just SO2 in water) has an odour resembling burnt matches (when dilute) and stings your nose (when more concentrated) Sulfurous acid has a bleaching effect on some dyes, while sulfuric acid doesn't.
  5. Question 1: (a), The ratio of NH4NO3:Na3PO4 is 3:1. 3 moles of NH4NO3 is approximately 240 grams while 1 mole of Na3PO4 is approximately 164 grams. 30 is 1/8 of 240. 1/8 of 164 is 20.5 grams. Clearly the limiting reagent is NH4NO3. (b), As NH4NO3 is the limiting reagent, the maximum amount of moles of product is 1/8 of the amount of moles of each product in the equation. Thus, The maximum amount of (NH4)3PO4 formed is 1/8 moles and the maximum amount of NaNO3 formed is 3/8 moles. You can work out the rest from here. ©, This can be worked out using the information I gave you in (a). Quest
  6. No, carbon dioxide is not polar. Although the C=O bond is somewhat polar, the molecule's symmetry balances out the polarity, resulting in a non-polar molecule. Thus, liquid CO2 is non-polar.
  7. weiming1998


    Stainless steel contains considerable amounts of chromium, which is in solution as trivalent Cr3+ ions. Iron is also dissolved in solution. However, it is in the form of Fe2+ ions that are a light grass-green in colour. The colour of Cr3+ is a much more intense deep green. Thus, stainless steel dissolved in hydrochloric acid yields a much deeper colour than iron dissolved in hydrochloric acid. I'm not sure why the solution looked greener after the addition of aluminium (optic effects due to precipitate of metal?), but the carbon-like particles are iron particles with traces of chromium in it.
  8. Dilute nitric acid (3.0 mol/L would be dilute) reacts with copper in a different equation as the NO2 formed would redissolve back/oxidize the copper in solution: 3Cu(s)+8HNO3(aq)----->3Cu(NO3)2(aq)+2NO(g)+4H2O(l) 2.5L of the solution contain 7.5 moles of nitric acid (3x2.5). Multiply that by 3/8 (every 8 moles of HNO3 reacts with 3 moles of Cu) and you get 2.8125. 2.8125 moles of copper had reacted. Multiply that by 64 (atomic weight of copper) and you get 180. 180 grams of copper had reacted. 500-180=320.
  9. Salt, or sodium chloride, is an ionic compound. That means that salt actually exists as Na+ and Cl- ions stacked together. The Na+ and the Cl- ions are bonded together with ionic bonds. As salt crystals dissolve in water, these bonds break, releasing Na+ and Cl- ions. Breaking bonds requires energy, so this is endothermic. But it doesn't stop here. The Na+ ion doesn't exist as free ions, as the negatively charged ends of water is attracted to and bonds to it, forming the coordination complex [Na(H2O)6}+, amongst other things. Bond-forming is exothermic, so this releases energy. I'm not sure
  10. The ferric nitrate definitely decomposed. At such high temperatures (180 degrees), a solution of ferric nitrate will decompose (hydrolyse), producing ferric oxides, ferric basic nitrates, and nitrogen oxides. A lot of transitional metal nitrates (copper, iron, etc) are very sensitive to the combination of water and high temperatures, and will decompose. The correct way to prepare hydrated iron (III) nitrate is by combining hydrogen peroxide (dilute nitric acid will not oxidise iron (II) to iron (III) easily), excess dilute nitric acid, and iron without heating, then evaporate (not boil) t
  11. The gelatinous blue mass sounds like copper (II) hydroxide to me. That's strange, because it should have dissolved already in the nitric acid. Or maybe it is precipitated hydrated copper (II) nitrate, which makes more sense. Anyway, just add water, and the mass should dissolve if it is the nitrate. If not, then add nitric acid, and it should dissolve.
  12. 1, I deducted it from the chemistry of silicon. Silicon dioxide dissolves in HF to form hexafluorosilicic acid. Zirconium dioxide acts very similarly to silicon dioxide, and as hexafluorozirconic acid exists, I deducted that it would form. To actually practically test it, heat the resulting solution of H2ZrF6 to dryness. If fumes of HF in addition to water (careful!) is emitted, then the compound is almost definitely H2ZrF6. 2, Yes, but the formation of these ions are negligible and won't affect anything in a 48% solution. H2F2 doesn't exist, as far as I know.
  13. An Arrhenius base is anything that increases the concentration of OH- in aqueous solution. In simpler terms, anything that causes the pH to rise above 7 when dissolved/mixed in water.
  14. Some HCl will be formed by adding salt to vinegar, but in very small amounts (an equilibrium), I think a mix of salt and vinegar cleans pennies due to the complexing ability of Cl-. Usually, the reaction between vinegar and copper oxide/sulfide is very slow due to the weak acidity of the vinegar. The vinegar dissolves the layer of oxides, forming [Cu(H2O)6]2+ and CH3COO-. What the chloride does, however, is allowing the formation of CuCl4(2-) within the solution. Thus, the equation can be written as: CuO(s)+2H+(aq)+4Cl-(aq)---->CuCl4(2-)+H2O. The chloride ions can also penetrate the oxide
  15. Ammonia has an extremely weak tendency to donate protons outside aqueous solution, forming amides and nitrides. Only extremely strong bases, like butyllithium (I think) can deprotonate ammonia. The pKa of ammonia is about 40, while the pKa of water is about 15-16. Arrhenius acids donates protons in AQUEOUS SOLUTION, while if a substance can donate protons at all, it is a Bronsted-lowry acid. Now it's your turn to think.
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