9. How many grams of magnesium hydroxide are needed to make 200mL of a 2.5M magn
ID: 1044138 • Letter: 9
Question
9. How many grams of magnesium hydroxide are needed to make 200mL of a 2.5M magnesium hydroxide solution? 10. What is the pH of the room temperature magnesium hydroxide solution produced in problem 9? 11. What is the concentration of a solution with a volume of 3.0 L containing 500g of calcium phosphate? 12. If a 50 mL portion of the solution produced on problem 11 is diluted to a final volume of 75 mL, what is the concentration of the new solution? 13. How much water should be added to 500mL of a 5.0 M silver chloride solution to make a 1.0M solution?Explanation / Answer
9)
volume , V = 200 mL
= 0.2 L
use:
number of mol,
n = Molarity * Volume
= 2.5*0.2
= 0.5 mol
Molar mass of Mg(OH)2,
MM = 1*MM(Mg) + 2*MM(O) + 2*MM(H)
= 1*24.31 + 2*16.0 + 2*1.008
= 58.326 g/mol
use:
mass of Mg(OH)2,
m = number of mol * molar mass
= 0.5 mol * 58.33 g/mol
= 29.16 g
Answer: 29.2 g
10)
[OH-] = 2*[Mg(OH)2]
= 2*2.5 M
= 5.0 M
use:
pOH = -log [OH-]
= -log (5)
= -0.699
use:
PH = 14 - pOH
= 14 - -0.699
= 14.699
Answer: 14.70
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