Brandon prepares a potassium hydroxide solution (KOH) that he uses during a titration to determine the unknown concentration of a hydrochloric acid solution
calculate the mass of potassium hydroxide that is need to prepare 250 cm^3 of a standard 0,125 mol.dm^-3 KOH solution.
Since 1 dm^3 = 1L,
.125 mol/dm^3 = .125M solution
So, the 250mL amount needs
.125*.250 = 0.03125 moles of KOH
multiply that by the molar mass of KOH to get the number of grams.
To calculate the mass of potassium hydroxide (KOH) needed to prepare the solution, we need to use the equation:
Number of moles = Volume (in dm³) x Concentration (in mol.dm⁻³)
Given data:
Volume of solution = 250 cm³
Concentration of KOH solution = 0.125 mol.dm⁻³
Firstly, we need to convert the volume from cm³ to dm³:
1 dm³ = 1000 cm³
So, 250 cm³ = 250/1000 dm³ = 0.25 dm³
Now we can use the equation to calculate the number of moles of KOH:
Number of moles = 0.25 dm³ x 0.125 mol.dm⁻³
= 0.03125 mol
Next, we need to determine the molar mass of potassium hydroxide (KOH):
K (potassium) = 39.10 g/mol
O (oxygen) = 16.00 g/mol
H (hydrogen) = 1.01 g/mol
Molar mass of KOH = K + O + H
= 39.10 g/mol + 16.00 g/mol + 1.01 g/mol
= 56.11 g/mol
Finally, we can calculate the mass of KOH needed using the following formula:
Mass (g) = Number of moles x Molar mass
= 0.03125 mol x 56.11 g/mol
= 1.753 g
Therefore, Brandon would need approximately 1.753 grams of potassium hydroxide (KOH) to prepare 250 cm³ of a standard 0.125 mol.dm^-3 KOH solution.