Analytical chemistry problems help?

H

HisashiH

New member
i need help solving these problems.. these are the only ones that get in my way for an exam

1. a 0.6334g sample of primary standard grade HgO (m.m. 216.59) was dissolved in 100ml of 0.5M KI solution. the Liberated OH needed 35.60 ml of HNO3 to reach end point. calculate the molarity of HNO3

2. Consider an impure sample of 25.20% Na2CO3. How many grams of the sample must be dissolved in a 500ml solution so that titration of a 50ml aliquot portion will require only about 22ml of 0.1250 M HCL to reach methyl orange end point

thanks a lot guys
 
Moles HgO = 0.6334 g/ 216.59 g/mol=0.002924
moles KI = 0.100 L x 0.5 M = 0.05
The reaction is :
HgO + 4 I- + H2O = HgI4- + 2 OH-
KI is the limiting reactant ( 0.002924 x 4 = 0.012 moles needed)

the ratio between HgO and OH- is 1 : 2
moles OH- = 2 x 0.002924=0.005848

OH- + HNO3 = NO3- + H2O
moles HNO3 = 0.005848
Molarity HNO3 = 0.005848 mol / 0.03560 L=0.1643 M


Na2CO3 + 2 HCl = H2O + CO2 + 2 NaCl
moles HCl = 0.022 L x 0.1250 M=0.00275
moles Na2CO3 = 0.00275/2=0.001375
Theoretical amount Na2CO3 = 0.001375 mol x 105.9876 g/mol=0.1457
g

mass sample = 100 x 0.1475 / 25.20= 0.5853 g
 
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