A substance, W has a concentration of 0.02mol when its molar mass was found to be 74.0 gmol-1 . Another substance V contains 1.00x1023 atoms and has molar mass of

40.0gmol-1. Which of the two substances has the greater mass (in grams)? [L =

6.02x1023]

ii) A 250 cm3

solution contains 14.63g of sodium chloride (NaCl). Calculate the

concentration of the solution in moldm-3

[Na= 23, Cl = 35.5]

Explanation:

mass of W in gram  = mole x molecular weight

= .02 x 74 = 1.48 gm

mass of V in gram

first of all we shall calculate the no of moles of V

1 mole = 6.0 x  10²³ atoms

1 x 10²³ atoms = 1 / 6 moles

mass of V in grams

= 40 / 6

= 6.67 grams .

So V has greater mass .

ii )

molecular weight of sodium chloride

= 58.5 gm

14.63 gram of sodium chloride

= 14.63 / 58.5 = .25 moles

250 cm³ = 250 x 10⁻³ dm³

So 250 x 10⁻³ dm³ of solution contains .25 moles of salt

1 dm³ of solution will contain .25 / 250 x 10⁻³ mole

= 1 mole

so concentration of solution is 1 mole per dm³

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