A solution with a total volume of 2.5 liters is composed of 31.4 grams of Na2S in water. What is the: molarity of this solution

             0.1608 mol/L

Explanation:

Calculate moles as,

Mole = Mass/M.Mass

Mole = 31.4 g / 78.045 g/mol

Mole = 0.402 mol

Now,

Molarity = Moles / Vol. in L

Molarity = 0.402 mol / 2.5 L

Molarity = 0.1608 mol/L

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the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.