Intro: A titration is a method of analysis that will allow you to determine the
precise endpoint of a reaction and therefore the precise quantity of reactant in
the titration flask. A burette is used to deliver the second reactant to the flask
and an indicator or pH Meter is used to detect the endpoint of the reaction.
Oxidation and reduction are best defined as follows. Oxidation occurs when the
oxidation number of an atom becomes larger. Reduction occurs when the oxidation
number of an atom becomes smaller. An easier way to remember this is OILRIG.
Oxidation Is Loss Reduction Is Gain
Questions
1. Which is oxidising agent and reducing agent?
a) Au3+(aq) + 2I-(aq) --> Au(s) + I2(s)
b) CuO + Mg --> Cu + MgO
c) 2 Na + Cl2 --> 2 NaCl
d) 2 K + H2 --> 2 KH
e) 4 Li + O2 --> 2 Li2O
f) 2 Na + O2 --> Na2O2
2. What volume of 0.200 M HCl is required for the complete neutralization of 1.10
g of NaHCO3 (sodium bicarbonate)?
3. What volume of 0.200 M HCl is required for the complete neutralization of 1.40
g of Na2CO3 (sodium carbonate)?
4. A sample of NaOH (sodium hydroxide) contains a small amount of Na2CO3
(sodium carbonate). For titration to the phenolphthalein endpoint, 0.200 g of
this sample requires 23.98 mL of 0.100 M HCl. An additional 0.700 mL of 0.100
M HCl is required to reach the methyl orange endpoint. What is the percentage
of Na2CO3 by mass in the sample?
Solutions/ Answers
1.
a) ox. agent: Au3+ , red agent: Ib) ox. agent: CuO , red agent: Mg
c) ox agent: Cl2 , red agent: Na
d) ox agent: H2 , red agent: K
e) ox agent: O2 , red agent: Li
f) ox agent: O2 , red agent: Na
2. First find out how many moles of NaHCO3 you have. Do this by figuring out
the molecular mass:
1Na (23.0) + 1H (1.008) + 1C (12.0) + 3O (16.00) =84.008 g/mole
1.10g (1mole/84.008g)=0.0131 moles of NaHCO3
Let v = volume of HCl
Assume one mole of HCl neutralizes one mole of NaHCO3.
v(0.200moles/L)=0.0131moles
v=0.0131moles/0.200moles/L
v=0.0655L or 65.5mL
3. Do this one the same way as number 2.
4. Phenolphthalein endpoint is for the strong base NaOH.
23.98mL (1L/1000mL)(0.100moles/L)=0.002… moles
molecular mass NaOH=23.0 + 16.0 + 1.008 =40.008g/mole
mass NaOH = 0.002398moles(40.008g/mole)=0.0959g
The methyl orange endpoint is for the Na2CO3.
0.700mL(1L/1000mL)(0.100moles/L)=0.000…
molecular mass is 2(23.0)+12.0 + 3(16.0)=106.0g/mole
mass Na2CO3= 0.0000700moles(106.0g/mole)=0.00742g
Total mass is 0.00742+0.0959=0.1033g
%Na2CO3=(0.00742g/0.1033g)100%=