#4 and #5:
To find pH given concentration of H+ or H30+
pH = - log (H+ or H30+ M)
To find pH given concentration of OH-
Since you already found the pH for this (in #4), you subtract #4's answer from 14.
14 - (pH) = pOH
5. B air is a mixture of many elements, but is not a chemically fused.
6. B Beef stew, composition varies throughout.
7. A. They can be chemically separated into their component elements, but they are all homogenous, and as such, have constant composition, which differs from the components properties, as the components must undergo a chemical change to become compounds.
I believe it is decomposition, neutralization, combustion
The density of He is 1.79 x 10⁻⁴ g/mL
In other words in 1 mL there's 1.79 x 10⁻⁴ g of He.
To fill a volume of 6.3 L the mass of He required
= 1.79 x 10⁻⁴ g/mL * 6300 mL
= 11 277 * 10⁻⁴ g
Therefore mass of He required = 1.1277 g of He
