Kindly help me wth my Pre-Lab, 1) Suppose you would like to make 100.00 mL of a
ID: 964466 • Letter: K
Question
Kindly help me wth my Pre-Lab,
1) Suppose you would like to make 100.00 mL of a 4.76 pH acetic acid/acetate buffer, in which the acid concentration is 0.070 M. What concentration of sodium acetate is needed in this buffer? 2) How many mL of 1.00 M acetic acid are needed for the buffer? 3) How many grams of sodium acetate are needed for the buffer? 4) Write the reaction of the buffer with HCl solution. How many mL of 0.100 M HCl can react with the buffer before it is exhausted? 5) Write the reaction of the buffer with NaOH solution. How many mL of 0.100 M NaOH can react with the buffer before it is exhausted?
Explanation / Answer
1)
pH = pKa + log [acetate / acetic acid]
4.76 = 4.76 + log [acetate / 0.07]
[acetate] = 0.070 M
total volume = 100 mL
2) volume of acetate = 50 mL
volume of acetic acid = 50 mL
because pH = pKa here : millimoles of acid = millimoles of base
3)
moles of acetate = 0.07 x 50 / 1000 = 3.5 x 10^-3
molar mass of sodium acetic acid = 82 g /.mol
mass of sodium acetate = 3.5 x 10^-3 x 82
= 0.287 g
4)
buffer with HCl solution :
CH3COO- + H+ ---------------> CH3COOH
5)
buffer reaction with NaOH
CH3COOH + OH- ----------------> CH3COO- + H2O
note : 4, 5 subpart problems i do not understand
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