OCR B Salter's Chemistry by Design F335 - 15th June 2015 Watch
But water does exist as both ice and liquid at the same temperature? On a cold day the top of a pond will freeze over but there will still be water underneath. In fact water exists as all three states at the same temperature, water vapour in the air, liquid as the pond, and solid as the frozen top of the pond (its even got a special name and occurs for other molecules as well - the triple point)
I'm not going to argue with that as I don't know enough on the subject of the "triple point". However the reason why water doesn't freeze in a pond is because the water at the top of the pond is in direct contact with the cold air which makes the top freeze however because ice is less dense than water it floats to the top and acts as a barrier of protection to the rest of the water underneath. This is why the top of the pond freezes but the rest of the water underneath is insulated enough (i.e. temperature is high enough) to still exist in it's liquid state.
Yes that is true and I probably chose a poor example, but if you imagine when the pond is just freezing over and the layer hasn't formed yet, the top of the pond will be at the same temperature but the ice crystals forming stay on the top of the water opposed to sinking, which is probably the concept the book is trying to get at
Well I may not have learnt anything from my revision today but at least I can now draw a hexagon really well
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Well, good luck everyone.
does that mean we HAVE to have the primary to gain the mark ?
Basically, as nitric is a strong acid, it fully dissociates. Therefore you have a 0.015 mol/dm3 concentration of H+ ions. However, the NaOH is a strong alkali so will neutralise the H+, but as you only have 10cm3 of NaOH versus the 20cm3 of HNO3, you can only have 10cm3 of acid left to provide H+ ions .
This means that you now have 10cm3 of 0.015 mol/dm3 solution of H+ ions.
To work out moles (conc x volume):
0.015 x (10/1000) = 1.5x10-4
-log(1.5x10-4) = 2.3
It was a very nasty question