Today's selection is:
1/ Question from Canada, "ammonia gas undergoes a combustion to produce nitrogen dioxide gas and water vapour. write and balance the equation"
Answer: 2NH3 +7/2O2 → 2NO2 + 3H2O
2/ Question from USA, "How do you convert weight percent to mass fraction?"
Answer: percent by mass (weight) = mass (weight) fraction x 100
3/ Question from USA, "what are the physical properties of metals due to metallic bonding?"
Answer: The physical properties of solid metals are:
- conduct heat
- conduct electricity
- generally high melting and boiling points
- malleable (can be hammered or pressed out of shape without breaking)
- ductile (able to be drawn into a wire)
- metallic lustre
- opaque (reflect light)
4/ Question from USA, "Can air be separated by physical means?"
Answer: Yes. Air is a mixture so it can be separated by physical means.
5/ Question from USA, "How do you calculate atomic mass from relative abundance?"
Answer: Given the relative atomic mass (r.a.m.) of an element and the mass of each of its isotopes, the relative abundance of each isotope can be calculated:
let y/100 = abundance of isotope 1
and (100 - y)/100 = abundance of isotope 2
then, r.a.m = [y/100 x mass isotope 1] + [(100 - y)/100 x mass isotope 2]
and solve for y
6/ Question from USA, "How do you turn empirical formula into molecular formula?"
Answer: molecular formula = whole number x empirical formula