1.59moles
Explanation:
Mass of CaO = 89.23g
Unknown
Number of moles = ?
Solution:
The mole is a unit of measurement in chemistry used to delineate the number of particles an atom contains.
A mole of a substance contains the avogadro's number of particles.
Number of moles = 
Molar mass of CaO = 40 + 16 = 56g/mol
Number of moles =
= 1.59moles
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Answer:
2.05*10⁻⁵ moles of CF₂ can dissolve in 100 g of water.
12.82 moles of CaF₂ will dissolve in exactly 1.00 L of solution
Explanation:
First, by definition of solubility, in 100 g of water there are 0.0016 g of CaF₂. So, to know how many moles are 0.0016 g, you must know the molar mass of the compound. For that you know:
- Ca: 40 g/mole
- F: 19 g/mole
So the molar mass of CaF₂ is:
CaF₂= 40 g/mole + 2*19 g/mole= 78 g/mole
Now you can apply the following rule of three: if there are 78 grams of CaF₂ in 1 mole, in 0.0016 grams of the compound how many moles are there?

moles=2.05*10⁻⁵
<u><em>2.05*10⁻⁵ moles of CF₂ can dissolve in 100 g of water.</em></u>
Now, to answer the following question, you can apply the following rule of three: if by definition of density in 1 mL there is 1 g of CaF₂, in 1000 mL (where 1L = 1000mL) how much mass of the compound is there?

mass of CaF₂= 1000 g
Now you can apply the following rule of three: if there are 78 grams of CaF₂ in 1 mole, in 1000 grams of the compound how many moles are there?

moles=12.82
<u><em>12.82 moles of CaF₂ will dissolve in exactly 1.00 L of solution</em></u>
Answer:
6
Explanation:
The atomic number for phosphorous is 15, meaning that it has 15 electrons (and protons). The first and second shells would be filled up with 2 and 8 electrons respectively, leaving 5 which goes on the third shell, which is also the valence shell, meaning phosphorous has 5 valence electrons.
Since the atomic number of sulfur is 16, the first and second shells are also filled up with 2 and 8 electrons respectively, leaving 6 to be on the third shell, the valence shell. Hence, sulfur has 6 valence electrons.