Posted by candy on Tuesday, September 21, 2010 at 3:12pm.
Yes, my NaOH is granular.
Why 7ml of 10M HCl? Do I add 7ml of 10M HCl 1st slowly in ice bath, then slowly adjust the pH to 7 using 10M HCl? Then to dilute to 15ml in a graduated cylinder?
Thanks
Posted by candy on Tuesday, September 21, 2010 at 10:03am.
The following is part of a procedure for a limit test for sulphates in an NaOH sample:-
Dissolve 3.0g of NaOH in 6ml of deionized water, adjust to pH 7 with HCl (approx.7.5ml) and dilute to 15ml with deionized water.
Please explain how to perform this procedure. Conc HCl or 1M HCl? I do not understand it.
Thanks.
Chemistry - urgent - bobpursley, Tuesday, September 21, 2010 at 10:09am
What form of NaOH did you use? Assume granular.
moles NaOH=3/40
moles HCl needed= 3/40=volume*Molarity
so lets see what 7 ml will neutralize
molarity=3/40/.007= or about 10Molar. 32Percent HCl is about 10M
didn't I just demonstrate it is conc HCl?
To perform the procedure for the limit test for sulphates in the NaOH sample, you will need to follow these steps:
1. Dissolve 3.0g of NaOH in 6ml of deionized water: Measure out 3.0g of NaOH and add it to a container. Then, add 6ml of deionized water to the same container.
2. Adjust the pH to 7 with HCl: Determine the amount of HCl needed to neutralize the NaOH. Assuming you used granular NaOH, calculate the number of moles of NaOH by dividing the mass of NaOH by its molar mass (40g/mol). In this case, it would be 3/40 moles. Since the NaOH and HCl react in a 1:1 ratio, you will need the same number of moles of HCl. Divide the moles of HCl by the volume of HCl to find the concentration needed. In this case, 3/40 divided by 0.007 (7ml converted to liters) would give you a molarity of around 10M.
3. Dilute to 15ml with deionized water: Add deionized water to the container until the volume reaches 15ml. This will dilute the solution.
In terms of the concentration of HCl to use, the previous calculation indicates that a concentration of 10M HCl is needed. You can use either concentrated HCl (32% HCl) or prepare a 1M HCl solution by diluting concentrated HCl with deionized water.