How do you prepare 250. mL of a 0.0100 M NaOH solution.

Question

How do you prepare 250. mL of a 0.0100 M NaOH solution. Do your calculation and discuss very well the step by step procedure in doing this. Apply the rules of significant figures.

Available glasswares and chemical reagents: a top loading balance, a 1-kg bottle of NaOH pellets, a small 50-mL beaker, a 500-mL volumetric flask, enough distilled water, 

Answer 1

Step 1: Always wear proper personnel protective equipment including gloves, clean lab coat, and goggles. Ensure hazard spill kits and eye wash stations are operational.

Step 2: Turn on the balance and allow to perform automated internal calibration.

Tip: Calibrate balances once a week using calibration weights. Turn on the balance at least two hours before you intend to use.

Step 3: Calculate how much sodium hydroxide is needed to make 250 ml of 0.0100 M solution. Molecular weight of NaOH is 39.997 g/mol.

Use this formula: Molarity = Weight (in grams)

----------------------------------------------------------------------

molecular weight (in g/mol) X Volume (in litres)

Weight (in grams) = Molarity (in M) X molecular weight (in g/mol) X Volume (in liters)

Thus, amount of NaOH required = 0.0100 M X 39.997 g/mol X 0.250 liter

= 0.099 g

To find the molecular weight of a compound, use periodic table and its chemical formula. Molecular weight can also be found quickly using free online platforms.

Step 4: Place the 50 ml beaker on the balance and press 'tare' or 'zero'. This allows the balance to normalize for the weight of the beaker.

Step 5: Using a spatula (if available), carefully weigh 0.099 g of NaOH. If a spatula is unavailable, tip the bottle slightly and add pellets to the 50 ml beaker one by one until desired weight is reached.

CAUTION: NaOH is corrosive and can cause chemical burns if handled with bare hands. Exercise caution when handling and ensure not to spill. In case of a spill, clean immediately following instructions on the MSDS for NaOH. In case of skin exposure, rinse the exposed skin with water immediately.

Step 6: In the 250 ml volumetric flask, add distilled water to 125 ml graduation mark.

Step 7: Add 0.099 g NaOH (pellet by pellet) slowly to the volumetric flask with water.

CAUTION: As this is an exothermic reaction (forms heat), NaOH should always be added to water first, and stirred gently. Consider keeping the flask on ice if preparing concentrated solutions.

Step 8: Add the remaining 125 ml distilled water to the flask and stir gently until dissolved.

Step 9: Once NaOH dissolves into solution, label the flask "0.0100 M NaOH".

TIPS:

If preparing concentrated stock solutions, store the solutions in properly labelled plastic containers in a cabinet.