Question
Chemistry
How many grams of CaCl2 are in 250 mL of 2.0 M CaCl2?
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The answer is:  " 56 g CaCl₂ " .
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Explanation:
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2.0 M CaCl₂  = 2.0 mol CaCl₂ / L  ;

Since: "M" = "Molarity" (measurement of concentration);

= moles of solute per L {"Liter"} of solution.
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Note the exact conversion:  1000 mL = 1 L .

Given: 250 mL ;

250 mL = ?  L  ?  ;

250 mL * (1 L / 1000 L) =  (250/1000) L = 0.25 L .
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(2.0 mol CaCl₂ / L ) * (0.25L) = (2.0) * (0.25) mol  = 0.50 mol CaCl₂ ;

We have: 0.50 mol CaCl₂ ;  Convert to "g" (grams):

→ 0.50 mol CaCl₂  .
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1 mol CaCl₂ = ? g ?

From the Periodic Table of Elements:

1 mol Ca = 40.08 g

1 mol Cl  =  35.45 g .

There are 2 atoms of Cl in " CaCl " ;

→ Note the subscript, "2", in the " Cl₂ " ;
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So, to calculate the molar mass of "CaCl₂" :

40.08 g  +  2(35.45 g) =

40.08 g  +  70.90 g = 110.98 g ;  round to 4 significant figures;

→ round to 111 g/mol .
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So:

→  0.50 mol CaCl₂  = ? g CaCl₂  ? ;

→  0.50 mol CaCl₂ * (111 g CaCl₂ / mol CaCl₂) ;

= (0.50) * (111 g) CaCl₂ ;

=  55.5 g CaCl₂  ;

→ round to 2 significant figures;

→  56 g CaCl₂ .
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The answer is:  " 56 g CaCl₂ " .
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