<u>Answer:</u> The moles of hydroxide ions present in the sample is 0.0008 moles
<u>Explanation:</u>
To calculate the concentration of acid, we use the equation given by neutralization reaction:
![n_1M_1V_1=n_2M_2V_2](https://tex.z-dn.net/?f=n_1M_1V_1%3Dn_2M_2V_2)
where,
are the n-factor, molarity and volume of acid which is HCl.
are the n-factor, molarity and volume of base which is ![Ca(OH)_2](https://tex.z-dn.net/?f=Ca%28OH%29_2)
We are given:
![n_1=1\\M_1=0.05M\\V_1=16mL\\n_2=2\\M_2=?M\\V_2=36.0mL](https://tex.z-dn.net/?f=n_1%3D1%5C%5CM_1%3D0.05M%5C%5CV_1%3D16mL%5C%5Cn_2%3D2%5C%5CM_2%3D%3FM%5C%5CV_2%3D36.0mL)
Putting values in above equation, we get:
![1\times 0.05\times 16=2\times M_2\times 36\\\\M_2=\frac{1\times 0.05\times 16}{2\times 36}=0.011M](https://tex.z-dn.net/?f=1%5Ctimes%200.05%5Ctimes%2016%3D2%5Ctimes%20M_2%5Ctimes%2036%5C%5C%5C%5CM_2%3D%5Cfrac%7B1%5Ctimes%200.05%5Ctimes%2016%7D%7B2%5Ctimes%2036%7D%3D0.011M)
To calculate the moles of hydroxide ions, we use the equation used to calculate the molarity of solution:
![\text{Molarity of the solution}=\frac{\text{Moles of solute}\times 1000}{\text{Volume of solution (in mL)}}](https://tex.z-dn.net/?f=%5Ctext%7BMolarity%20of%20the%20solution%7D%3D%5Cfrac%7B%5Ctext%7BMoles%20of%20solute%7D%5Ctimes%201000%7D%7B%5Ctext%7BVolume%20of%20solution%20%28in%20mL%29%7D%7D)
Molarity of solution = 0.011 M
Volume of solution = 36.0 mL
Putting values in above equation, we get:
![0.011=\frac{\text{Moles of }Ca(OH)_2\times 1000}{36}\\\\\text{Moles of }Ca(OH)_2=\frac{0.011\times 36}{1000}=0.0004mol](https://tex.z-dn.net/?f=0.011%3D%5Cfrac%7B%5Ctext%7BMoles%20of%20%7DCa%28OH%29_2%5Ctimes%201000%7D%7B36%7D%5C%5C%5C%5C%5Ctext%7BMoles%20of%20%7DCa%28OH%29_2%3D%5Cfrac%7B0.011%5Ctimes%2036%7D%7B1000%7D%3D0.0004mol)
1 mole of calcium hydroxide produces 1 mole of calcium ions and 2 moles of hydroxide ions.
Moles of hydroxide ions = (0.0004 × 2) = 0.0008 moles
Hence, the moles of hydroxide ions present in the sample is 0.0008 moles