I got a lot of small numbers in my calculations. I just want to make sure I\'m u

Question

I got a lot of small numbers in my calculations. I just want to make sure I'm using the right equations.

Volume of saturated Ca(OH)2 solution (mL) Concentration of standardized HCl solution (mol / L) Buret reading, initial (mL) Buret reading, nal (mL) Volume of HCl added (mL) Moles of HCl added (mol) Moles of OH- in saturated solution (mol) [HO-], equilibrium (mol / L) [Ca2+], equilibrium (mol / L) Average molar solubility of Ca(OH)2 (mol / L) Ksp of Ca(OH)2 Average Ksp Standard deviation of Ksp Appendix B Relative standard deviation of Ksp (%RSD) Appendix B

Explanation / Answer

Moles of HCl:

1) 0.044 M * 0.0154 l = 0.000678

2) 0.044 M * 0.0217 l = 0.000955

3) 0.044 M * 0.0154 l = 0.000678

use the titration eq: M1V1=M2V2

1) M[Ca(OH)2] = 0.000678 / 0.025 = 0.027 M

2) M[Ca(OH)2] = 0.000955 / 0.025 = 0.038M

3) M[Ca(OH)2] = 0.000678 / 0.025 = 0.027 M

Ca(OH)2 ----> Ca2+ + 2OH-

In equilibrium [OH-] = 2*[Ca(OH)2]; [Ca2+] = [Ca(OH)2] (I'm not going to repeat this last one, just copy the numbers from above)

1) M[(OH)-] = 2* 0.027 M = 0.054 M

2) M[(OH)-] = 2 * 0.038M = 0.076 M

3) M[(OH)-] = 2* 0.027 M = 0.054 M

moles of OH- in saturated solution= V * M

1) moles (OH)- = 0.025 * 0.054 M = 0.00135 moles

2) moles (OH)- = 0.025 * 0.076 M = 0.0019 moles

3) moles (OH)- = 0.025 * 0.054 M = 0.00135 moles

Avergare molar solubitity = (0.027+0.038+0.027)/3 = 0.031 mol/L

1) Ksp = [Ca2+]*[OH-]2 = 0.027*0.0542 = 7.9*10-5

2) Ksp = 0.038*0.0762 = 2.2*10-4

3) Ksp = 0.027*0.0542 = 7.9*10-5

Average Ksp = 1.3*10-4

Please calculate the standard deviation by yourself because it's too long.

Hope this help!

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