How many moles of solid Mg(OH)2 should you add to 200mL of 0.15M lactic acid solution to produce pH 4.0 buffer?
See your post later (above).
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To find out how many moles of solid Mg(OH)2 should be added to the lactic acid solution to produce a pH 4.0 buffer, we need to set up a balanced chemical equation for the reaction between lactic acid and magnesium hydroxide.
The balanced equation for the reaction between lactic acid (C3H6O3) and magnesium hydroxide (Mg(OH)2) is:
2C3H6O3 + 3Mg(OH)2 → Mg3(C3H5O3)2 + 6H2O
From the equation, we can see that 2 moles of lactic acid react with 3 moles of magnesium hydroxide, producing 1 mole of magnesium lactate and 6 moles of water.
To determine how many moles of magnesium lactate are needed to reach a pH of 4.0, we need to calculate the concentration of the lactic acid solution after neutralization. Since it is a buffer solution, the acid and base components react in a 1:1 ratio, resulting in a pH equal to the pKa of the acid. The pKa of lactic acid is around 3.9 - 4.1.
Since the initial concentration of the lactic acid solution is 0.15 M and it reacts in a 1:1 ratio with magnesium hydroxide, the concentration of the lactic acid after neutralization will be 0.15 M.
Therefore, to achieve a pH 4.0 buffer, we need to neutralize 0.15 moles of lactic acid.
From the balanced equation, we can see that 2 moles of lactic acid react with 3 moles of magnesium hydroxide. So, the number of moles of magnesium hydroxide needed can be calculated as:
(0.15 moles lactic acid) * (3 moles Mg(OH)2 / 2 moles lactic acid) = 0.225 moles Mg(OH)2
Therefore, you should add approximately 0.225 moles of solid Mg(OH)2 to the 200 mL of 0.15 M lactic acid solution to produce a pH 4.0 buffer.
Please note that this is a theoretical calculation. In practice, it is essential to consider the solubility of magnesium hydroxide and the volume contraction that may occur during the addition of the solid compound.