NaOH is sold commercially as Lye.?

Question

A 1.2g sample of lye required 45cm3 of 0.5 moldm-3 HCl for neutralisation. Calculate the % by mass of NaOH in the Lye.

Question is how do I do this because i'm awful at maths.

Answer 1

The number of moles of acid used for neutralisation = volume (in Litres) x concentration = 0.045 x 0.5 = 0.0225 moles.

From the equation for the reaction it can be seen that the same number of moles of NaOH are used as the acid.

NaOH + HCl = NaCl + 2H2O

So there must also be 0.0225 moles of NaOH

The mass of NaOH = number of moles x formula mass (Na : 23 + O : 16 + H : 1) = 0.0225 x 40 = 0.9g NaOH

So the % NaOH in the Lye is 0.9/1.2 x 100 = 75%

Answer 2

This is a titration equation:

NaOH + HCl ----> NaCl + H2O (A 1:1 reaction)

So working out the amount of HCl gives you the amount of NaOH.
moles HCl= concentration x volume (in dm3)
= 0.5 moldm-3 x (45/1000)dm3

the moles HCl = moles NaOH

work out the mass = moles x RMM

(RMM= sum of atomic masses 23+16+1= the grams per mole)

Express this as a percentage of 1.2g

xg/1.2g X 100.

Answer 3

OK, first you need to figure out how much HCl you used. It's 0.5 mol/dm^3, but your volume is in cm^3. A cm is 1/10 of a dm, so multiply the volume by (1/10)^3, or 1/1000, to get it into dm^3. That means you used 0.045 dm^3 of the HCl. Now, multiply the moles per dm^3 by the number of dm^3s to get the number of moles: 0.5 * 0.045 = 0.0225 moles of HCl.

HCl and NaOH neutralize in a 1:1 ratio, so 0.0225 moles of HCl could neutralize 0.0225 moles of NaOH. So now you know how much NaOH was in the sample.

Next, you have to convert this number of moles into a mass. The molar mass of a molecule is equal to the sum of the atomic masses of the atoms in it--the mass of Na (22.990 g/mol), the mass of O (15.999 g/mol) and the mass of H (1.007 g/mol). These add up to 39.996 g/mol. One mole of NaOH weighs 39.996 grams. Multiply the weight of a mole by the number of moles to get the total weight of NaOH: 0.0225*39.996 = 0.900 grams.

Finally, to calculate the % by weight, divide the mass of NaOH (0.900) by the mass of lye (1.200) to get 0.75, then multiply by 100%: 75%.

Answer 4

California and Oregon want to regulate and tax it. It will be interesting to see how they intended to override Federal drug laws. For years, States have all too willingly bowed to the power of the mighty Fed Gov. For the last 40 years, they should have been telling Fed Gov to go pound sand with every little piece of legislation they came out with that didn't directly deal with trade or defense (starting with RvW). Its the State's Right to determine whether or not they will allow abortion. It's the State's right whether or not they will require sex offenders to register. It's the State's Right to run their own education system. It's the State's Right to demand that the Fed Gov protect their borders with foreign nations against illegal intrusions. It's the State's Right to determine the use of marijuana and other similar drugs. The Fed Gov has been overstepping it's authority for years and people who are ignorant to the powers of Government have been content to let them. Time for the States to take back their Rights.