Aqueous Sodium Hydroxide Solution from Pellets: 6N Make-Up in Oman

Most labs and plants in Oman use caustic soda as an aqueous sodium hydroxide solution. You make it by dissolving sodium hydroxide pellets or flakes in cold water. A 1 litre batch of 6N solution needs 240 g of pure NaOH, which is 250 g of pellets at a 96% assay. Add the solid to the water in small portions, never the water to the solid. Then let it cool, make it up to volume and check the strength by titration.

Sodium hydroxide pellets and flakes: same chemical, different handling

Sodium hydroxide (caustic soda, NaOH, CAS 1310-73-2) is a white hygroscopic solid sold as flakes, pellets, beads and prills. The form does not change the chemistry. Industrial caustic soda flakes typically contain 98-99% NaOH. They are made by membrane-cell electrolysis of brine, then evaporated and flaked.

The form changes how you weigh and dissolve it. Pellets pour evenly and make less dust on a lab balance, so QC and water-testing labs use them for titration solutions. Flakes suit plant make-up tanks, where you tip a whole drum into a dissolving vessel.

Our sodium hydroxide flakes / pellets (RXSOL-19-1618-025) have the specification below. Always calculate a make-up from the assay on the label, because a few points of carbonate and moisture change the result.

How much NaOH goes into an aqueous sodium hydroxide solution

For NaOH, normality equals molarity because each formula unit gives one OH- ion. This means 6N and 6M are the same solution. To find the grams of pure NaOH needed for 1 litre, multiply the normality by 40. Then divide by your assay as a decimal to get the weight of pellets or flakes to use. The table gives both figures, for a 96% and a 99% product. A % w/v figure gives the grams in 100 mL of finished solution.

The 20% w/v line matches the pharmacopoeia reagent: dissolve 20 g NaOH in water and dilute to 100 mL. NaOH is very soluble in water, so even the 50% w/v make-up dissolves fully at room temperature. It gives off a lot of heat as it dissolves, which the next sections cover.

6N NaOH solution preparation, step by step

This method makes 1 litre of 6N solution from pellets at a 96% assay. For larger batches, scale every quantity in proportion.

1. Put on splash goggles, a face shield, nitrile or neoprene gloves and a chemical apron. Work in a ventilated area with an eyewash within reach.
2. Measure about 800 mL of cold water (about 80% of the final volume) into an HDPE or PP beaker. Stand the beaker in an ice bath.
3. Weigh 250 g of pellets quickly and reseal the drum at once, because the solid picks up moisture and carbon dioxide from the air.
4. Add the pellets slowly, a small portion at a time, to the surface of the water while stirring constantly. Never pour water onto the pellets.
5. Let the solution cool to room temperature.
6. Transfer it to a 1000 mL plastic volumetric flask or a marked HDPE bottle. Make up to 1000 mL with water and mix well.
7. Standardise the solution before precise use. The pharmacopoeia method titrates it against 1 M hydrochloric acid with methyl orange as indicator.

The order of addition matters because dissolving NaOH is strongly exothermic: the hydration releases roughly 44.5 kJ/mol. Water poured onto solid caustic, or caustic added to hot water, can boil locally and spatter corrosive liquid out of the vessel.

Caustic soda dilution from a 6N stock (C1V1 = C2V2)

Many labs keep one 6N stock and dilute it as needed. Multiply the strength you want by the volume you want, then divide by the stock strength. For 1 litre of 1N, you need 1 x 1000 / 6 = 166.7 mL of 6N stock. For 1 litre of 2N you need 333.3 mL, and for 1 litre of 0.1N you need 16.7 mL. Put most of the water in the flask first and add the stock to the water. Then make up to the mark and mix.

Heat, humidity and containers on Oman sites

A typical dilution runs 20-40 °C above ambient, and concentrated make-ups can go above 60-85 °C. The standard advice is to start with cold water at about 15-25 °C. In a Muscat or Sohar summer, water from a rooftop tank can already be 30 to 35 °C, and a strong batch made with it can come close to boiling. Use chilled water, add the solid in small portions and allow cooling time between additions. In a plant tank, add the drum in several lots with the agitator running.

Coastal humidity in Muscat, Sohar and Salalah causes a second problem. NaOH absorbs moisture and carbon dioxide from the air. This is why it is not a primary standard, and why a stored solution slowly loses strength as carbonate forms. Reseal opened drums immediately, use opened stock quickly and re-standardise solutions before critical titrations. If carbonate matters for your analysis, the pharmacopoeia gives a low-carbonate method. You dissolve NaOH to 50% w/v in water that has had its carbon dioxide removed, let it stand so the carbonate settles, then decant the clear liquid while keeping air out.

Store solutions in HDPE or PP bottles with tight caps. Aqueous NaOH slowly attacks glass, so ground-glass stoppers and joints can seize. Never use aluminium, tin, lead, zinc or galvanised steel for caustic, because NaOH attacks these metals and gives off flammable hydrogen. Keep it away from ammonium salts, which release ammonia. Store the solid dry and well closed in the original container, away from strong acids, metals, food and feedstuffs. The store should have no drain or sewer access.

Hazards, PPE and first aid for caustic soda

Sodium hydroxide carries the signal word DANGER with three hazard statements: H290 may be corrosive to metals, H302 harmful if swallowed, and H314 causes severe skin burns and eye damage. The exposure limit is TLV 2 mg/m3 ceiling, and the NIOSH IDLH is 10 mg/m3. Dust from tipping flakes therefore needs to be controlled.

Wear chemical splash goggles plus a face shield, nitrile or neoprene gloves and a chemical apron. Use a particulate respirator where dust is present. Flush skin or eye contact with plenty of water and get medical help. Sweep spilled solid into covered plastic containers, and never pour water into the solid. For transport, the solid is UN 1823, Class 8, packing group II. The solution is UN 1824, Class 8, packing group II-III.

Where aqueous NaOH is used in Oman

Food and dairy plants around Muscat and Barka use caustic solutions for CIP cleaning of tanks and lines. Water and sewage treatment plants use it to control pH in drinking water and wastewater. For those buyers we list a sewage treatment grade (RXSOL-40-1318-050). Labs at plants, ports and universities use 0.1N and 1N solutions for titration. Oil and gas refineries use caustic wash, and soap makers use NaOH for saponification.

To read more about the product itself, see our sodium hydroxide flakes and pellets supplier page for Oman. The wider range is in our guide to inorganic powder chemicals in Muscat.

Where to buy sodium hydroxide pellets in Muscat and Oman

Muscat Chemical (Muscat & Barka for Business Trading), Barka Industrial Area, Sultanate of Oman. Phone +968 77333599, WhatsApp +968 77333599, email muscatchem@gmail.com.

We pack sodium hydroxide flakes / pellets in 50kg. M.S. Drum with inside double lining. We are based in Barka Industrial Area and supply buyers across Oman. The same product is also listed on our Sohar site. Buyers in Dhofar can order through our Salalah sodium hydroxide page. Send us the quantity, the part number and the delivery site, and ask for the MSDS with your quote. If you also need acids or indicators for the same job, browse all our products.

To order, request a quote or send your requirement on WhatsApp to +968 77333599.

Frequently asked questions

Is 6N NaOH the same as 6M NaOH?

Yes. Sodium hydroxide gives one OH- ion per formula unit, so its normality equals its molarity. A 6N solution and a 6M solution both contain 240 g of pure NaOH in each litre.

How many grams of NaOH do I need for 1 litre of 1 M or 6 M solution?

You need 40 g of pure NaOH for 1 M and 240 g for 6 M, each made up to 1 litre. Divide by the assay of your product. At a 96% assay, that is 41.7 g and 250 g of pellets.

Why must caustic soda be added to water and not water to caustic?

Dissolving NaOH releases a lot of heat, roughly 44.5 kJ/mol. Water poured onto the solid boils where it touches the solid and spatters corrosive liquid. Adding the solid slowly to cold water while stirring spreads the heat through the whole volume.

Can I store sodium hydroxide solution in a glass bottle?

Use HDPE or PP bottles with tight caps instead. Aqueous NaOH slowly attacks glass, and ground-glass stoppers can seize in the neck. Do not use aluminium, zinc or galvanised containers either, because NaOH attacks them and gives off hydrogen.

How do I dilute 50% caustic soda to a weaker solution?

Work by mass for w/w solutions. To make 1000 g of 10% w/w, weigh 800 g of cold water and slowly add 200 g of 50% w/w caustic while stirring. Ready-made 50% w/w solution has a typical density of about 1.5 g/mL at 25 °C, so weigh it rather than measuring by volume.