Question

Show calculation step by step for:

1) 0.10% (wt/vol) ethanol

2) 10% (wt/vol) H2SO4 solution

3) 10% (wt/vol) sodium tungtate

4) 1N NaOH solution

5) Saturated HgCl2 solution

6) saturated K2CO3 solution

7) prepared a solution of 8.5015g of K2Cr2O7 and 400mL sulfuric acid per liter of solution

Answer 1

1. For 1 L. Weight 1 g ethanol, put it in a 1000 mL graduated cylinder and add water to sign.
2. For 1 L. Weight 102 g H2SO4 98%. Put in a Beryelius beaker about 500 mL water. Add slowly the acid in the beaker. Allow to cool. Never put water over this acid. Eventually use a water bath to cool the mixture. Transfer it in 1000 mL cylinder, add water to sign. Transfer in a bottle and mix well.
3. For 1 L. Dissolve 100 g sodium tungstate in about 500 mL water. Transfer in a graduated cylinder and add water to sign.
4. For 1 L. Weight about 41.00 g NaOH, wash it with water to remove Na2CO3. Disolve it in about 500 mL water. Transfer the solution in 1000 mL volumetric flask . Add water to sign. Do a titration and calculate the correction factor for the concentration.
5. For 100 mL. Put about 8.0 g HgCl2 in 100 mL water at room temperature. Mix and wait for the undissolved salt to settle. Decant the solution that is now saturated.
6. For 100 mL. Put about 60 g Na2CO3 monohydrate in 100 mL water. Mix, wait to settle, decant.
7. It is a preparation for a primary standard. It must be very exact.

Primary standard: procedure

1. K2Cr2O7 chemical dried at 103-105 ºC for 2 h & cooled in desiccator.

2. Weigh 8.5015g g in a clean, oven dried, cooled & tared watch glass.

3. Carefully transfer weighed chemical to a funnel placed on 1L volumetric flask.

4. Wash the watch glass with a small amount of water into the funnel.

5. Add about 0.5L distilled water, swirl to dissolve & make up to 1L mark.

6. Carefully/slowly add the acid. Cool the flask in a water bath.

6. Store the reagent in a reagent bottle (not in volumetric flask).