0.688 g of antacid was treated with 50.00 mL of 0.100 M HCl. The excess acid required 4.21 mL of 1.200 M NaOH for back titration. What is the neutralizing power of this antacid expressed as mmol(millimoles) of HCl per gram of antacid?
mmols HCl added initially = mL x M = 5.00
mmols NaOH to neutralize = 4.21 x 1.2 = 5.05.
Check you numbers. mmols NaOH > mmols HCl which means antacid tablet did not neutralize any of the HCl.
To find the neutralizing power of the antacid as mmol of HCl per gram of antacid, we need to calculate the amount of HCl that reacts with the antacid.
First, we need to calculate the number of moles of HCl used in the reaction.
Number of moles of HCl = volume of HCl solution (in L) × concentration of HCl solution (in mol/L)
Given that the volume of HCl solution used is 50.00 mL (or 0.050 L) and the concentration of HCl solution is 0.100 M, we can calculate:
Number of moles of HCl = 0.050 L × 0.100 mol/L = 0.005 mol
Now, let's calculate the number of moles of HCl that reacted with the antacid. Since they react in a 1:1 ratio, the number of moles of HCl that reacted is also 0.005 mol.
Next, we need to calculate the number of moles of HCl that remained after reacting with the antacid. We can do this by taking into account the amount of NaOH used in the back titration.
Number of moles of NaOH used in the back titration = volume of NaOH solution (in L) × concentration of NaOH solution (in mol/L)
Given that the volume of NaOH solution used is 4.21 mL (or 0.00421 L) and the concentration of NaOH solution is 1.200 M, we can calculate:
Number of moles of NaOH = 0.00421 L × 1.200 mol/L = 0.00505 mol
Since the reaction between NaOH and HCl is also 1:1, the number of moles of HCl that reacted with NaOH is 0.00505 mol.
Therefore, the number of moles of HCl that remained after reacting with the antacid is 0.005 mol - 0.00505 mol = -0.00005 mol.
However, we cannot have a negative amount of moles, so the excess amount of HCl that remained is 0 mol.
Next, we need to calculate the number of moles of HCl per gram of antacid.
Number of moles of HCl per gram of antacid = number of moles of HCl / mass of antacid (in grams)
Given that the mass of antacid used is 0.688 g, we can calculate:
Number of moles of HCl per gram of antacid = 0.005 mol / 0.688 g
Finally, we can convert this value to millimoles per gram by multiplying by 1000:
Neutralizing power of the antacid = (0.005 mol / 0.688 g) × 1000
Therefore, the neutralizing power of this antacid expressed as mmol of HCl per gram of antacid is the calculated value from the equation above.