HKDSE Chemistry Question Review (2021-01-21)

1. Explain why semen is alkaline.

Solution:

It contains hydrogencarbonate ions. Carbon dioxide is removed from bloodstream such that more oxygen will be available for male genital to ejaculate.

When semen passes through cervix, the latter has lactic acid such that the former will be neutralized to release carbon dioxide, which is endothermic, and water, which is exothermic. Overall, the pH and composition of semen secure the transport of speeds which enter the womb within acceptable temperature ranges.

speeds --> sperms

fucking Samsung auto-correction

2. Explain why oxalic acid is toxic.

Solution: It will form a stone to upset kidneys with calcium ions. Oxalic acid is dibasic such that the packing of the stone will be largely ionic, in a sense that hydrogen bonds are difficult to form with water molecules. So Calcium oxaliate is insoluble in water and cannot be metabolized.

Calcium oxalate*

3. How do snails eat concrete?

Solution:

Snails have many microscopic teeth to physically digest concrete composed of calcium sulphate. Once the calcium ions are escaped from the ground concrete, the proton in their digestive juice will replace calcium ions with to form sulphuric acid to be egested.

4. Why is urine smelly?

Solution:

The urine smell is actually ammonia.

Urea + water + heat --> CO2 + 2NH3

5. Why should we never eat shit?

Solution:

Bile is composed of cholesterol.

It is a metabolic waste from liver.

Bile then sticks on the stool.

Also, by diffusion colons will accumulate I read on the stool to give bad smells.

So why should we eat toxins?

will accumulate urea*

Colon has many bacteria. They will also produce toxins to promote tumor formation. So eating shit is eating carcinogens.

6. How to dissolve bones?

Solution: By halogenic acids.

6HF + Ca3(PO4)2 --> 3 CaF2 + 2 H3PO4