I'm a bit worried about the question about traditional sources if alkalis. I put urea. But in the book it says stale urine. I'm not sure if urea and stale urine is the same thing. As it's the urea IN the urine that forms the alkali. I think it was 2 marks so it would be really annoying to lose two marks for something that could have been prevented. Does anyone's know if urea is still an acceptable answer, it's the only question which is stressImg me out. Thanks.