A beaker contains 100 mL of water. We add 112 mg of KOH(s). What is the concentration of H+ ions?
To determine the concentration of H+ ions, we need to calculate the number of moles of KOH that is added to the water. From there, we can find the number of moles of H+ ions present.
To calculate the number of moles of KOH, you need to use its molar mass. The molar mass of KOH is:
K (potassium) = 39.10 g/mol
O (oxygen) = 16.00 g/mol
H (hydrogen) = 1.01 g/mol.
So, the molar mass of KOH is:
39.10 g/mol + 16.00 g/mol + 1.01 g/mol = 56.11 g/mol
Next, we convert the mass of KOH added (112 mg) into grams:
112 mg = 112/1000 g = 0.112 g
Now, we can calculate the number of moles of KOH:
Number of moles = mass/molar mass = 0.112 g/ 56.11 g/mol
Number of moles of KOH = 0.001994 mol
Since KOH is a strong base, it dissociates completely in water to produce one K+ ion and one OH- ion. Therefore, the number of moles of H+ ions is equal to the number of moles of OH- ions. Thus, the concentration of H+ ions is given by the equation:
[H+] = Number of moles of H+ ions / Volume of solution
The volume of the solution is given as 100 mL, which is equal to 0.1 L.
[H+] = 0.001994 mol / 0.1 L
[H+] = 0.01994 mol/L
Therefore, the concentration of H+ ions is 0.01994 mol/L.