<p>^Amphoteric. That was Al.</p>
<p>Aluminium oxide and hydroxide are amphoteric.
Al3O2 + H+ → Al3+ + H2O
Al3O2 + OH- → [Al(OH4)]-</p>
<p>Hydroxide is a way similar.
It was just asked the day before the subject test in my school exam.</p>
<p>Chemistry was rather easy. The only one I have a doubt on is the question where it asked if H2 can be displaced by water displacement and its reason.</p>
<p>H2 should be less dense than air and it should be able to be displaced by water, but the reason of the latter should be due to its lower density than water rather than air.</p>
<p>There was a question like this? i dont remember it 
Seriously i did not even read this one, im sure :O</p>
<p>There was a diagram of the apparatus too. This was one of the TF TF CE questions. Right page, top most question ;)</p>
<p>i think the answer for the h2 displacement by water is not becz of density but becz h2 is not soluble in water …</p>
<p>for example u cant collect HCl over water becz it dissolves in water</p>
<p>but h2 u can becz it doesnt dissolve …</p>
<p>so i think the answer is T F</p>
<p>anyone remember other TF TF CE questions that were hard/confusing ?</p>
<p>OH this was one of the last questions right? I skipped this one. the second one i skipped. The one with an inverted test tube?</p>
<p>Yeah, it’s that one only</p>
<p>@crisronaldo : I put in TT without CE, that is hydrogen gas is both less dense than air and can be collected by water displacement. But I want to clarify one point, that the density is absolutely one of the considerations of air or water displacement of gas. Because if a gas is more dense than the medium, say air displacement of xenon gas, is not feasible. But it xenon gas soluble in air? Absolutely not. Solubility is of course another consideration, but it has nothing to do with the judgment involving this question.</p>
<p>When we are collecting a gas over water, all we care is whether the gas is soluble or not; and we know we can only collect nonpolar gas because polar gas is too soluble in water. Density is definitely not an issue for water displacement; as long as the nonpolar gas is less dense than water, it will be able to rise above water and be collected. (No gas is more dense than water at normal condition)</p>
<p>OK I get it, it still doesn’t change the answer right? Since the two statements are related to air and water respectively. If the statement changes to ‘hydrogen is less dense than water’, then it will render the question confusing.</p>
<p>Yup, the answer is still TT and no CE, you are right :D</p>
<p>Damn. I thought Hydrogen gas was slightly soluble in water and put down FT…</p>
<p>Whew. I had no time to do it anyway.</p>
<p>It is true that hydrogen gas is slightly soluble; but comparing to a polar gas, it is insignificant. For example, NH3 has a solubility of 500g per kg of water and H2 has a solubility of 0.0015g per kg of water.</p>
<p>I thought the test was fairly good, hopefully we will all get good scores, what do you guys predict the curve will be like? (Like this many questions right to get 800, 750, or 700 and above)</p>