If element X has 25 protons, how many electrons does it have?
2 answers:
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Answer:
\text{0.30 cm}^{3} \times \left (\dfrac{10^{-2}\text{ m}}{\text{1 cm}}\right )^{3} = 3.0 \times 10^{-7} \text{ m}^{3}
Explanation:
0.030 cm³ × ? = x m³
You want to convert cubic centimetres to cubic metres, so you multiply the cubic centimetres by a conversion factor.
For example, you know that centi means "× 10⁻²", so
1 cm = 10⁻² m
If we divide each side by 1 cm, we get 1 = (10⁻² m/1 cm).
If we divide each side by 10⁻² m, we get (1 cm/10⁻² m) = 1.
So, we can use either (10⁻² m/1 cm) or (1 cm/10⁻² m) as a conversion factor, because each fraction equals one.
We choose the former because it has the desired units on top.
The "cm" is cubed, so we must cube the conversion factor.
The calculation becomes
Answer:
394.76g
Explanation:
Given parameters:
Mass of Phosphorus = 172.1g
Unknown:
Mass of P₂O₅ = ?
Solution:
We should work from the known specie to the unknown in this problem. The limiting reactant is the reactant in short supply and it determines the extent of the reaction. This is the given phosphorus.
Oxygen is in the excess.
The balanced reaction equation:
4P + 5O₂ → 2P₂O₅
let us find the number of moles of phosphorus first,
Number of moles of phosphorus =
Molar mass of phosphorus = 31g/mole
Number of moles = = 5.55mole
4 moles of phosphorus gives 2 moles of P₂O₅
5.55 mole of P will produce = 2.78moles
Mass of P₂O₅ = number of moles x molar mass
Molar mass of P₂O₅ = (31 x 2) + (16 x 5) = 142g/mole
Mass of P₂O₅ = 2.78moles x 142g/mole = 394.76g