***SHOW WORK WITH MY NUMBERS FOR POINTS*** 1. The concentration of a hydrochlori
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Question
***SHOW WORK WITH MY NUMBERS FOR POINTS***
1. The concentration of a hydrochloric acid solution is approximately 0.25 M but the solution must be standardized by titration against sodium hydroxide to determine the precise concentration. If the molarity of the sodium hydroxide solution is 0.2070 M and the volume required to reach the end point in the titration against 25.00 mL of the hydrochloric acid is 29.40 mL,
what is the molarity of the hydrochloric acid solution?
2. Using an analytical balance, 0.1659 grams of the nickel(II) ammine complex was weighed by difference and placed in an Erlenmeyer flask. Exactly 25 mL of the standardized hydrochloric acid solution was added to neutralize the ammonia in the complex. The excess hydrochloric acid remaining in the Erlenmeyer flask was titrated against the sodium hydroxide. 13.84 mL of sodium hydroxide was required to reach the end point.
How many moles of sodium hydroxide were required?
3. This equals the number of moles of excess HCl remaining in the flask. How many moles of HCl are there in 25.00 mL of the hydrochloric acid solution, and therefore how many moles of HCl were required to neutralize the ammonia in the nickel(II) ammine complex?
Moles of HCl in 25.00 mL =
Moles of HCl required to neutralize the ammonia =
4. This equals the number of moles of ammonia in your sample of the complex. Multiply by 17.031 to obtain the mass of ammonia. Subtract this from the mass of the complex (0.1659 grams) to obtain the mass of nickel ions and nitrate ions in the sample.
Mass of ammonia in the sample = g
Mass of Ni(NO3)2 in the sample = g
5. Divide this mass by 182.70 to obtain the number of moles of Ni(NO3)2 in the sample and then calculate the mole ratio of Ni(NO3)2 to ammonia in the complex.
Moles of Ni(NO3)2 in the sample =
Mole ratio of ammonia to Ni(NO3)2 in the complex =
***SHOW WORK WITH MY NUMBERS FOR POINTS***
Explanation / Answer
Answer for 1)
mL x M = millimoles
29.4 mL x 0.2070 M = 6.0858 millimoles NaOH
25.00 mL x HCl Molarity = 6.0858 millimoles HCl
Therefore, HCL molarity = 6.0858/25 = 0.2434 M
Answer for 2)
it took 13.84 mL of NaOH to reach the endpoint, and we also know that its concentration is 1 mole per 1 Liter
so, we can set up an equation, 1000 mL make 1 Liter, and 1mol / 1L represents the molar concentration.
molarity of NaOH is given 0.2070 M
No. of moles of NaOH = 0.2070 * 13.84/1000 = 2.865 * 10-3 mol
Answer for 3)
Moles of HCl in 25.00 mL = 0.2070 * 29.40/1000 = 6.086 *10-3 mol
all we do is subtract the moles of NaOH from the moles of HCl in 25 mL.
6.086 *10-3 - 2.865 * 10-3 mol= Moles of HCl required to neutralize the ammonia = 3.2208 * 10-3 mol
Answer for 4)
Mass of ammonia in the sample = 17.031 * 3.2208 * 10-3 g= 0.05485 g
Mass of Ni(NO3)2 in the sample = 0.1659 - 0.5485 g= 0.11105 g
Answer for 5)
Moles of Ni(NO3)2 in the sample = 0.11105/ 182.70 = 6.078 *10-4 mol
no. of moles of ammonia = 3.2208 * 10-3 mol
Mole ratio of ammonia to Ni(NO3)2 in the complex =(3.2208 * 10-3) / (6.078 *10-4) = 5.2988
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