Answer:
The influenza virus is mutated every 20-40 years.
Explanation:
Large mutations occur every 20-40 years. This results in a new influenza virus to which the human population has no protection. These large mutations are almost always followed by an influenza pandemic.
Hope this helps!
Answer:
165.726 g.
Explanation:
- For the balanced equation:
<em>Cr₂O₃ + 3H₂S → Cr₂S₃ + 3H₂O,</em>
It is clear that 1 mol of Cr₂O₃ and 3 mol of H₂S to produce 1 mol of Cr₂S₃ and 3 mol of H₂O.
- Firstly, we need to calculate the no. of moles of 324.8 g of chromium(III) sulphide:
no. of moles of Cr₂S₃ = mass/molar mass = (324.8 g)/(200.19 g/mol) = 1.62 mol.
- Now, we can find the "no. of grams" of H₂S are needed:
<u><em>Using cross multiplication:</em></u>
3 mol of H₂S produces → 1 mol of Cr₂S₃, from stichiometry.
??? mol of H₂S produces → 1.62 mol of Cr₂S₃.
∴ The no. of moles of H₂S are needed = (3 mol)(1.62 mol)/(1 mol) = 4.86 mol.
∴ The "no. of grams" of H₂S are needed = (no. of moles of H₂S)(molar mass of H₂S) = (4.86 mol)(34.1 g/mol) = 165.726 g.
6.11% w/v of Cu2+ implies that 6.11 g of Cu2+ is present in 100 ml of the solution
therefore, 250 ml of the solution would have: 250 ml * 6.11 g/100 ml = 15.275 g
# moles of Cu2+ = 15.275 g/63.546 g mole-1 = 0.2404 moles
1 mole of CuCl2 contain 1 mole of Cu2+ ion
Hence, 0.2404 moles of Cu2+ would correspond to 0.2404 moles of CuCl2
Molar mass of CuCl2 = 134.452 g/mole
The mass of CuCl2 required = 0.2404 moles * 134.452 g/mole = 32.32 grams
Answer: 8.7 grams
Explanation:
According to avogadro's law, 1 mole of every substance occupies 22.4 L at STP and contains avogadro's number 
of particles.
To calculate the moles, we use the equation:
As oxygen is in excess, Aluminium is the limiting reagent and limits the formation of products.
According to stoichiometry:
4 moles of aluminium give = 2 moles of 
Thus 0.17 moles of aluminium give=
Mass of 
Thus the mass of is 8.7 grams
Theyre the big bunched up group in the middle of the periodic table
