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Five involved pH and pOH problems

1. If the pH of an aqueous solution is 8.23, what are the hydrogen- and hydroxide-ion concentrations of this solution?
2. If 7.40 grams of Ca(OH)2 is dissolved in sufficient water to make 100mL of solution, what is the hydroxide-ion concentration of this solution?
3. What is the hydroxide-ion concentration, the pH, and the hydrogen-ion concentrations of solutions containing 15.0 grams of the following substances in 1.00L solution:

*First, write the balanced equations for the reactions that occur when the oxides are dissolved in water.

Substance Molarity of Substance [OH-] pH [H3O+]
CaO
Na2O

4. If 50mL of 0.50 M HCl solution is added to 75mL of 0.20 M Ca(OH)2 solution, will the solution be neutral, acidic, or basic? Write a balanced chemical equation for the reaction and justify your answer?
5. Complete and balance. Predict oxide to be acidic, basic, or amphoteric.

Zn + O2 
Ga + O2 
As4 + O2 
Li + O2 

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Thank you,
Professor K

1. If the pH of an aqueous solution is 8.23, what are the hydrogen- and hydroxide-ion concentrations of this solution?
Since pH = -log[H+] where [H+] = the hydrogen ion concentration, you simply take the inverse log of -8.23 to get the hydrogen ion concentration, 5.89x10-9
Then, there are several ways to get the hydroxide ion concentration. You can use the fact that pH + pOH = 14 (take the inverse log of -(14-8.23)) or that [H+] + [OH-] = 1x10-14 (subtract the answer above from 1x10-14)
Thus, [OH-] = 1.70x10-6
2. If 7.40 grams of Ca(OH)2 is dissolved in sufficient water to make 100mL of solution, what is the hydroxide-ion concentration of this solution?
So, assume that the entire amount dissolves. First you must convert the 7.40g to moles by dividing by the molecular weight. If you're ever not sure whether to multiply or divide, just check the units... 7.40g Ca(OH)2 x (1 mol ...

Solution Summary

1.Calculate concentrations of H+ and OH- given a pH value. Fully explained solution.
2.Calculate the OH- concentration given an amount in grams of dissolved base. Fully explained solution.
3.Calculate H+ and OH- concentrations and molarity given 15g of various substances dissolved in water. Fully explained solution.
4.Predict whether a solution is acidic, basic, or neutral given two volumes of acid and base that are mixed. Fully explained solution.
5.Balance 4 equations and predict whether the oxide is acidic, basic, or neutral. Fully explained solution.

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