When 93 mL of distilled water is added to 188 mL of 2.91 M MgCl2, what is the new concentration?
Answer to 2 decimal places.

Explanation:

The concentration is 2.91 moles / Liter.

The moles don't change when the new water of 93mL is added.

Starting number of moles

C = 2.91 moles / Liter

m = ?

V = 1 Liter. = 1000 mL

C = m/V

2.91 moles / L = m/1 Liter

2.91 moles in 1 Liter

Moles in 188 mL

2.91 moles / 1000 mL = x moles / 188 mL      Cross multiply

2.91 moles * 188 mL = 1000 x

547 moles mL = 1000 mL x                             Divide by 1000

547 moles mL

   = x

1000 mL

0.547 moles in 188 mL

Now add 93 mL to 188 mL

281 mL

Finally  calculate the concentration.

C = 0.547 moles / 281 mL

C = 0.00194  moles / mL

C = 1.93 moles / L

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