recipitates when excess potassium chloride is added to 10. If 12.8 g lead(II) su
ID: 636020 • Letter: R
Question
recipitates when excess potassium chloride is added to 10. If 12.8 g lead(II) sulfate (303.26 g/mol) precinit sample, what is the molar concentration of Pb' in a. 0.0696 M b. 0.0422 M c. 0.0256 M d. 0.129 M e. 0.776 M ded to sodium hydroxide is added to 75.0 mL of 0.200 M iron(lIn) nitratep a te if 50.0 mL of 0.500 a. 1.60 g b. 0.891 g c. 3.56 g 11. How many grams of iron (III) hydroxide (106.87 g/mo) will yr d. 8.02 g e. 2.67 g 12. What is the oxidation number of sulfur in the thiosulfate ion (S2O a. +2 e. +1Explanation / Answer
10.
Mass of PbSO4 = 12.8 grams
molar mass of PbSO4 = 303.26 gram/mole
volume of water= 1.65L
Number of moles of PbSo4 = mass/molar mass = 12.8/303.26 = 0.0422 moles
Molarity = number of moles/volume
Molarity = 0.0422/1.65 = 0.0256 M
PbSo4 ------------------ Pb+2 + SO4-2
So the concentration of Pb+2 = 0.0256M
The answer is C
11.
SOdium Hydroxide = NaOH= 50.0ml of 0.500M
number of moles of NaOH= 0.500Mx0.050L =0.025 moles
Iron(III)Nitrate = 75.0mL of 0.200M
number of moles of Fe(NO3)3 = 0.200Mx0.075L= 0.015 moles
Fe(NO3)3(aq) + 3 NaOH(aq) -------------------- Fe(OH)3(s) + 3 NaNO3(aq)
according to equation
1 moles of Fe(NO3)3 = 3 moles of NaOH
0.015 moles of Fe(NO3)3 = ?
= 3x0.015/1= 0.045 moles of NaOH
we need 0.045 moles of NaOH. but we have 0.025 moles of NaOH. so NaOH is first completed in the reaction. Hence NaOH is limiting reagent.
according to equation
3 moles of NaOH = 1 moles of Fe(OH)3
0.025 moles of NaOH= ?
= 1x0.025/3= 0.0083 moles of Fe(OH)3
number of moles of Fe(OH)3 formed = 0.00833 moles
molar mass of Fe(OH)3 = 106.87gram/mole
mass of 0.0083 moles of Fe(OH)3 = 0.00833x106.87 =0.8902 grams
mass of Fe(OH)3 formed = 0.891 grams.
The answer is B.
12.
S2O3-2
The oxidation state of Oxygen is -2
sum of the oxidation states of all the atoms in a poly atomic ion is equal to its charge.
2x+3(-2) = -2
2x-6 = -2
2x= +4
x= +2
The oxidation state of Sulfur =+2
The answer is A.
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