Dear Margarita:

There should be any problem. Solubility of NaCl in water is 359 g/L, and a 5M solution is 292 g/L. Check your calculation.

Best regards

Is this solution in pure (distilled or otherwise purified lab-grade) water? If so, the solubility at 25°C of NaCl in water is around 5.9 moles/L,so like the previous answer said, you should be ok. Just dump all the solid NaCl into the water, put a stir bar and stir until it all dissolves. Dissolution of NaCl may be slow when getting closer to saturation, but it should all dissolve. You're using lab-grade, at least 95% pure NaCl, right? 

Try mixing with some mild heat and/or ultrasonication to help it go into solution (e.g. place the covered container in a heated ultrasonic bath).

I do  not recommend to head at all. 5M NaCl should be soluble at room temperature. If there is some problem with the product and you dissolve it on heating, the sample will precipitate when going back to RT. Just stir until it dissolve. If, it is not dissolved, try to find another analytical-grade product, at least 99% pure.

"mild" heat should be fine, but I agree that we should emphasize hi grade water and high purity NaCl should be used.

I think the issue is the purity of my compound might be the issues since I was only able to dissolve it when I heated it up to 50C for 15 minutes. I will look for high purity NaCl, thank you so much for your help!!

Mild heat  (2-3 minute in microwave) will solve ur problem of  undissolution of NaCl. it works when there is the high concentration of NaCl. Heating increases the molecules movement and this increases fast collision and easy dissolution of  solid chemicals.

I have realized what could be the problem. Surely not the NaCl quality because most of the companies produce a product with purity higher than 99.5%. The question is that NaCl  solubility increases with temperature and you can dissolve more at 50ºC, than at 25ºC. If you try to dissolve the 292 g in less than 1 L, (i.e. 500 ml) you are trying to get a 10M solution, and this is not possible at 25ºC. Then, when you fill to 1 L, after dissolving at higher temperature, you get your right concentration, but if you dissolve directly in about 1L, let say 980 ml, at 25ºC, and then fill to 1L, you should get any problem.

I have also the same problem even i  added 15 to 25 microlitter hcl but the condition is same

As I noted much earlier in this thread, some mild heat is all that is needed to get it into solution. If you have access to an ultrasonic bath, place the container in it initially to speed up the process, then remove and stir on a warm hot plate (hot plate/stir).

can i autoclave it cz i need 6M solution

If the salt doesn't dissolve in maximum volume, add water in drops above the limit with constant stirring. The salt would dissolve in seconds. However the concentration would be slightly less than 5M. This is how I had to prepare one.

It is usually very difficult to prepare 5M NaCl solution for the one who is doing this for the first time.

The easiest method to prepare 5M NaCl solution is:

(1)    Take little dH2O in a conical flask and add the required amount of NaCl little by little with constant stirring,

(2)    Autoclave the solution, as the temperature of the solution becomes lowered (40-50C), all the remaining salt will dissolve in seconds by shaking, then level volume of the solution up to the mark by adding more water, if not levelled. It is an efficient method; I have personally used it.

Slightly Warm the solution at 500c and stirring can solve the issue. 

Mild heating will not solve, salt will precipitate again as the solution cools down to RT. Better to mix overnight at RT. If needed in a rush, either autoclave or settle for a 4M, which will dissolve promptly.

Sometimes, the purity of the salt can be a problem. If the NaCl salt is not molecular grade, you can prepare 4M stock solution(you can t,here preparing your working solution from this 4M), I suggest that the solution should not be heated otherwise it will precipitate at room temperature thereafter.

I also have same problem when I made 6M NaCl solution, it could not be dissolved very well. Then i autoclaved it but the solution still not be dissolved.

Please, read my previous anwser to this question. I think it should be useful.

It’s really strange that I tried to prepare 1mL 5M NaCl solution and it dissolved successfully while when I tried to prepare 500mL it failed.

Those interested at this discussion topic may possibly want to check also: https://www.researchgate.net/post/How_can_I_dissolve_6_molar_sodium_chloride

So I had this problem. I took a beaker measured 292.2 g of NaCl into it, put a stir bar in, turned on stirring, added water upto the 1000 mL mark with stirring and resorted to mild heating. After an hour, all the salt had still not dissolved. Out of deep exasperation I decided to make a 4M solution instead and calculated that it can be achieved by making the final volume 1250 mL instead of 1000 mL. So I added water upto the 1200 mL mark and kept stirring. All the salt dissolved magically. Now when I poured the solution into a measuring cylinder, I noticed that the solution in my beaker had a volume of just a little bit more that 1000 mL. So I added extra water to get 1250 mL.

I realized that I could have indeed achieved 5M by not trusting the marks on the beaker. So try this: keep on adding water slowly till your solution runs clear. Then pour it into a volumetric flask/measuring cylinder and add water to get 1 L. At room temperature 5M NaCl solution should not be a problem. Do not trust beaker marks ever.

The salt should dissolve at 6M Concentration (358g/L). If its not dissolving means there are two possibilities. 1 The salt may be contaminated or not pure. and 2. the water you are using may be not correctly distilled. if the water has already dissolved salt in that, it may affect the further dissolving of salt.