## Define-what-is-concentration-of-solution

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Question:If I'm given different concentrations of a strong acid and a strong base with phenolphthalein indicator, how am I supposed to figure out, by mixing the acids and bases together, what the concentrations of the acids and bases are?

Answers:The process is called titration. For example, you can have an unknown quantity of acid dissolved in water. You add a very small amount of phenolphthalein to this solution and it is clear. You slowly add very small quantities of a strong base, such as sodium hydroxide, and keep mixing the solution. When a pink color appears and stays permanently (even after swirling) you have added enough sodium hydroxide solution to neutralize the acid. Since you were measuring the quantity of sodium hydroxide added, you can calculate the quantity of base, and from this you can calculate the quantity of acid in your unknown mixture of acid that you dissolved to make the original solution.

Question:Potassium hydrogen phthalate, often abbreviated KHP, can be obtained in high purity and is used to determine the concentrations of solutions of strong bases. Strong bases react with the hydrogen phthalate ion as follows. HP -(aq) + OH -(aq) H2O(l) + P2-(aq) The molar mass of KHP is 204.2 g/mol and Ka for the HP - ion is 3.1 multiplied by 10-6. (a) If a titration experiment begins with 0.4885 g of KHP and has a final volume of about 100 mL, which indicator(s) from the figure above (http://i31.tinypic.com/x26nbn.png) would be most appropriate? (Choose all that apply.) thymol blue, bromthymol blue, phenolphthalein, methyl red, methyl violet, methyl orange, alizarin yellow R (b) If the titration required 39.33 mL of NaOH solution to reach the end point, what is the concentration of the NaOH solution?

Answers:(a) In cases like this, you look for a color change around a pH which equals the pKa of the acid. The pKa is 5.5 and methyl red is the only indicator that has a color change that brackets pH = 5.5 (b) 0.4885 g / 204.2 g/mol = 0.002392262 mol of KHP 0.002392262 mol / 0.03933 L = 0.06082 M There is a 1:1 molar ratio between KHP and NaOH, which is why I used 0.002392262 mol for the NaOH.

Question:Having major problems with this. Please help! Answer these questions. Show your work. 16. What is the molar concentration (i.e., molarity) of sucrose (C12H22O11) if 150.0 g is dissolved in 250.0 mL of solution? 17. What is the molar concentration of methanol (CH3OH) if 125.0 mL is dissolved in enough water to make 15.0 L of solution? The density of methanol is 0.792 g/mL. 18. How many grams of NaOH are contained in 250.0 mL of a 0.400 M sodium hydroxide solution? 19. The drinking water standard for lead is 15 ppb (parts per billion). What is this in M? 20. What volume of 0.650 M sucrose must be diluted with water to prepare 250.0 mL of 0.423 M sucrose? 21. Which of the following solutions contains the largest concentration of chloride ions: a. 100 mL of 0.30 M AlCl3 b. 50.0 mL of 0.60 M MgCl2 c. 200.0 mL of 0.40 M NaCl

Answers:16. Molar mass = 342 g/mol Moles = 150 / 342 = 0.439 M= 0.439 / 0.250 L = 1.75 M 17. Mass = 125 x 0.792 = 99 g Molar mass = 32 g/mol Moles = 99 / 32 = 3.09 M = 3.09 / 15 = 0.206 18. Moles = 0.250 x 0.400 = 0.10 Molar mass = 40 g/mol 40 x 0.1 = 4.0 g 19. 1 ppb = 1 mg / 1 m^3 = 1 mg / 1000 L 15 mg = 0.015 g Moles = 0.015 / 207.2 = 0.000072 M = 0.000072 / 1000 = 7.2 x 10^-8 20. 0.25 x 0.423 = V x 0.65 V = 0.163 L = 163 mL 21. a. 0.3 x 0.1 = 0.03 moles AlCl3 => moles Cl- = 0.09 b. 0.05 x 0.6 = 0.03 moles MgCl2 => moles Cl- = 0.06 c. 0.2 x 0.4 = 0.08 moles NaCl => 0.08 moles Cl-

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