On the last page of the pink booklet (mole calculations)
Question 3a is How many moles of hydrogen in every mole of HCl?
What does this mean? Because surely it's a compound so to work out moles of hyrdogen is meaningless. Am I missing something here?
Thanks.
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6 comments:
You don't need to do any calculations for this type of question, it's just to get you used to looking at the ratio of the elements in a compound to each other.
So, in every 1 mole of HCl there is 1 mole of H and 1 mole of Cl. But in every 1 mole of H2SO4, there are 2 moles of H, 1 mole of S and 4 moles of O.
Hope this makes sense!
Ok thanks, I didn't think it could be that simple.
Another question:
A carboxyl group,COOH, is called an acidic group, and exists in ethanoic and methanoic acid etc. Why does it release H+ ions in solution, rather than OH- ions?
Great question, Vicky!
It's related to the difference in electronegativity between O and H. O is highly electronegative compared to H, so in the O-H covalent bond the shared pair of electrons is already 'nearer' the O. This means that it is easy for the O-H bond to break and therefore for the carboxylic acid to behave as a Bronsted-Lowry acid by donating an H+ ion.
Hope this helps!
Ok thanks. Here's my next question:
When talking about ionic and covalent bonding and getting 'a full outer shell' what does that mean when you get beyond the first few shells and you fill up the next number shell before finishing the previous one? ie filling 4s before 3d, because then whenever you 'finish' filling a shell, you've started on the next one, so can never finish filling a shell. Or do you abandon the idea of trying to fill shells?
By the way, today, Jo and I started our presentation but didn't finish it. I'm sorry if that messes up where we are supposed to be in terms of lessons.
Don't worry about not finishing your presentation, Vicky. I've planned for us to do some practical work on Wednesday that is based on Claire, Jennifer, Debbie and Rhiannon's areas of the topic but we have at least 1 lesson next week in which to come back to intermolecular forces. Which bits did you manage to get done?
When thinking about electrons at AS level and beyond, we tend to think about filling 'energy levels' rather than shells. For an atom to be stable, it should have a full energy level. However, it is also favourable for it to have a full sub-level (e.g. 2s, 3p) and also, to a lesser degree, a half-full sub-level (e.g. 3d5).
The reason that 4s is filled before 3d (in neutral atoms only, not charged ions) is because 4s is lower in energy than 3d and sub-levels are filled in order of increasing energy.
Not sure if I've answered your question or not but hope I've helped!
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