62.5 mL is prepare .
What is molarity?
Molar concentration is a unit of measurement for the concentration of a chemical species, specifically a solute, in a solution, expressed as the amount of substance per unit volume of solution. The most often used unit for molarity in chemistry is the number of moles per litre, denoted by the unit symbol mol/L or mol/dm3 in SI units.
Molarity of the stock solution as 0.100 M
Volume of the dilute solution as 250 mL
Molarity of dilute solution as 0.0250 M
We are required to calculate the Volume of the stalk solution.
Taking the volume and molarity of the stock solution to be V₁ and M₁ respectively, and volume and molarity of the dilute solution to be V₂ and M₂ respectively.
We are going to use the dilution formula;
According to the dilution formula, M₁V₁ = M₂V₂
Rearranging the formula;
V₁ = M₂V₂ ÷ M₁
= (0.025 M × 0.25 L) ÷ 0.100 M
= 0.0625 L
But, 1 L = 1000 mL
V₁ = 62.5 mL
Therefore, the volume of the stock solution is 62.5 mL
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Answer:
moles = given mass/atomic mass
so H2O mass = 2 +16=18
so 12g of h2o= 12/16 = 3/4 moles
Formula units in 450 g of 
is 1.93 × 10²⁴ formula units.
<u>Explanation:</u>
First we have to find the number of moles in the given mass by dividing the mass by its molar mass as,
Now, we have to multiply the number of moles of Na₂SO₄ by the Avogadro's number, 6.022 × 10²³ formula units/mol, so we will get the number of formula units present in the given mass of the compound.
3.2 mol × 6.022 × 10²³ = 1.93 × 10²⁴ formula units.
So, 1.93 × 10²⁴ formula units is present in 450g of Na₂SO₄.
