Question

how does one prepare a 100ppm sanitizing solution of chlorine and water?
add 1 part chlorine bleach to 9 parts water
add 5ml of chlorine bleach to 1l of water
add 2ml of chlorine bleach to 1l of water
none of the above

Explanation:

Step1: Convert units

1 ppm = 1 mg/L. So 100 ppm = 100 mg/L = 0.1 g/L.
Chlorine bleach (sodium hypochlorite, NaClO) has a typical active chlorine content. Assume the chlorine bleach has 5% (mass/volume) active chlorine. That is 50 g/L.

Step2: Use dilution formula

Let \(V_1\) be the volume of bleach and \(V_2\) be the volume of the final solution (\(V_2 = 1L\)).
Using \(C_1V_1=C_2V_2\), where \(C_1 = 50g/L\), \(C_2=0.1g/L\), \(V_2 = 1L\)
\(V_1=\frac{C_2V_2}{C_1}=\frac{0.1g/L\times1L}{50g/L}=0.002L = 2mL\)

Answer:

C. Add 2mL of chlorine bleach to 1L of water