**Molarity of 50% (w/w) Sodium Hydroxide (NaOH)**

**Overview:**

- Sodium hydroxide is a clear colourless liquid. A 50% (w/w) concentrated Sodium hydroxide can be obtained from different suppliers.
- 50% (w/w) Sodium hydroxide means that 100 grams of solution contains 50 grams of NaOH.
- The density of 50% (w/w) Sodium hydroxide is 1.515 g/ml at 25°C that means that weight of the 1 ml of Sodium hydroxide solution is 1.22 gram at 25°C.
- Molarity refers to number of moles of the solute present in 1 litre of solution.
- In simple words, 1 mole is equal to atomic weight of the substance. For example, 1 mole of Sodium hydroxide is equal to 40.00 grams of Sodium hydroxide (NaOH, molecular weight = 40.00).

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**Calculation:**

**Known values:**

Concentration of Sodium Hydroxide: 50% (% by mass, wt/wt)

**Step 1: Calculate the volume of 100 grams of Sodium Hydroxide solution.**

**Formula**:

Volume = weight / density

Volume of 100 gram of Sodium hydroxide solution: 100/1.515 = 66.0066 ml

Note: 50% (w/w) Sodium Hydroxide means that 100 grams of solution contains 50 grams of Sodium Hydroxide.

**The volume of 100 grams of Sodium hydroxide solution is 66.0066 ml. That means 50 grams of NaOH is present in 66.0066 ml of Sodium hydroxide solution.**

**Step 2: Calculate how many grams of NaOH is present in 1000 ml of Sodium hydroxide solution.**

1000 ml of Sodium Hydroxide will contain = 1000 x 50/66.0066 = 757.50 grams of NaOH

**1000 ml ofSodium hydroxide solution will contains 757.50 grams of NaOH.**

**Step 3: Calculate number of moles of NaOH present in 757.50 grams of NaOH.**

757.50 grams of NaOH will be equal to = 757.50 x 1/40 = 18.9375 moles

**Therefore, we can say that 1 litre ofSodium hydroxide solution contains 18.9375 moles or in other words molarity of 50% (w/w) Sodium Hydroxide is equal to 18.9375 M.**