0. What is the main reason that sodium hydroxide is not considered a good candid
ID: 695637 • Letter: 0
Question
0. What is the main reason that sodium hydroxide is not considered a good candidate to be a primary standard? (A) Sodium hydroxide is relatively expensive. (B) Sodium hydroxide is hygroscopic. (C) Sodium hydroxide has low solubility in water. (D) Sodium hydroxide has a low molar mass. . A 25.00-mL volume of 0.1000 M HCI solution is added to 25.00 mL of a NaOH solution of unknown concentration. The resulting solution requires 10.00 mL of 0.05000 M NaOH to back titrate to a phenolphthalein endpoint. What is the molarity of NaOH in the unknown? (A) 0.1000 M (B) 0.2000 M (D) 0.1800 M (C) 0.08000 M A solution that has a K concentration of 5.00 ppm is to be prepared from solid, primary standard grade KCI. KCI Assuming a solution density of 1.000 g-mL-', how many milligrams of KCI must be used to make 1.00 L of solution? Molar Masses 39.10 g mol 74.55 g.mol A) 2.62 mg C) 5.00 mg (B) 9.53 mg (D) 9.53×10, mgExplanation / Answer
10. answer: B
NaOH is hygroscopic,means it absorbs water moisture present in atmospheric air.results chnage in concentration.
11. no of mol of NaOH consumed for back titration = 10*0.05/1000 = 5*10^-4 mol
No of mol of HCl taken = 25*0.1/1000 = 0.0025 mol
No of mol of NaOH added = (0.0025)-(5*10^-4) = 0.002 mol
Concentration of NaOH added = n/V = 0.002*1000/25 = 0.08 M
answer: C
12. concentration of K+ = 5 ppm
we know that, 1 mol K+ = 1 mol KCl
so taht,
concentration of KCl = 5 ppm
1 ppm = 1 mg/L
amount of KCl required = 5 mg
answer: C
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