two compounds. b. The density of fluorosilicic acid (H2SiF6) is related to its p

Question

two compounds. b. The density of fluorosilicic acid (H2SiF6) is related to its per- cent by weight as shown in Figure c 1250 1200 b1150 1100 1050 1000 0 4 8 12 16 20 24 28 32 Concentration in % w/w H2SiF6 FIGURE c Density of Fluorosilicic Acid at 20°C Source: http://www.m/2rconsultancy.com/Pages/H2SiF6DATA.aspx i. Calculate the mass, in kg, of fluoride ion in 100.0 lbs of 25.0% (weight/weight) commercial fluorosilicic acid. For a mixture of two components, A and B, the % (weight/ weight) means the weight of component A (lbs.) in the total weight (lbs.) of the contents- weight of A+ weight B ii. Calculate the molarity of the dilute (25.0% weight/ weight) fluorosilicic acid.

Explanation / Answer

Basis : mass of commercial H2SIF6 =100 lb

mass % of H2SIF6 =25%

mass of H2SIF6 in the sample =100*25/100 =25 lb

1 lb =0.4535 kg

25 lb= 25*0.4535 kg =11.34 kgs

moles of H2SiF6 = mass/molar mass = 144

moles of H2SiF6= 11.34/144 kg moles =0.07875 kg moles

H2SiF6 ------------>2H++Si+2+6F-

so 1 mole of H2SiF6 contains 6 F+ ions

0.07875 kg moles of H2SiF6 contain 6*0.07875 kg moles of F+=0.4725 kg moles

molar mass of F- = 19 kg/k moles

mass of F - = 0.4725*19 kg=8.9775 kg

density of the solution is obtained by drawing a horizontal line at 25% weight and intersecting the line given. Then from the intersection point draw a horizontal line and intersecting the y-axis. This density is 1175 kg/m3.

moles off H2SiF6= 0.07875 kg moles= 0.07875*1000 gmoles =78.75 gmoles

Molarity is moles of solute per liter of solution

volume of solution = mass/ density = 100/1175 =0.085 m3 =0.085*m3= 1000L/m3=85 L

molarity = moles/ Liter of solution= 78.75/85 =0.93

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