Question

1. Prepare 1 mmol/L Lithium standard from lithium carbonate (Li2CO3). Give the quantity in mg/L.

2. If 3 mL of a 100 mcg/mL is diluted to 100 mL. What is the concentration in mg/dL?

3. Prepare 1L of 0.06M NaOH (FW 40) solution from 1N stock solution.

4. Prepare 2L of 0.85% (W/V) NaCl (FW 58).

5. Prepare a 5% W/V calcium chloride solution from CaCl2 * 6H2O (FW 219).

Answer 1

1. Molarity = (w/Mwt)*(1/V in L)

molarity = 1/2 = 0.5 mM of Li2CO3 = 1 mM of Li+

mwt of Li2CO3 = 73.891 g/mol

    0.5 = (x/73.891)*(1/1)

x = 36.94 mg

so take 36.94 mg of Li2CO3 and dissolve in minimum amount of water, and then add water upto 1 L solution.

2. 100 mcg/mL = 0.1 mg/ml

so that,

   c1V1 = c2V2

(0.1*3) = C2*100

C2 = concentration of solution = 0.003 mg/ml

1 ml = 0.01 dl

C2 = concentration of solution = 0.003/0.01 = 0.3 mg/dl

3. for NaOH , Normality = Molarity

so that,

Molarity = (w/Mwt)*(1/V in L)
  
   0.06 = (w/40)*(1/1)

w = weight of NaOH = 2.4 g

take 2.4 g NaOH and dissolve in minimum amount of water, and then add water upto 1 L solution.

4. 0.85%(w/v) , means 0.85 g of solute present in 100 ml sample.

   so that, mass of NAcL required = 2000*0.85/100 = 17 g

take 17 g NaCl and dissolve in minimum amount of water, and then add water upto 2 L solution.

5.

5%w/v , means 5 g of solute present in 100 ml sample.

so that,  

take 5 g of CaCl2*6H2O and dissole in litte amount of water and then add water up to 100 ml solution.