What is the molarity of 4 moles of NaOH in 500 ml solution?

Kitty F.

asked • 12/05/14

I'm working on a solutions lab and would like someone to look over my calculations please.

The question asked:

"What mass of solid NaOH is needed to make 500mL of 0.1M NaOH solution?"

My work:

Needed: 500mL solution with a final concentration of .1M

Na: 22.989 amu

O: 15.999 amu

H: 1.008 amu

=39.996 amu (rounded to 40amu)

40 amu= 1 mole NaOH

To make one mole NaOH solution, dissolve 40 grams NaOH in 500mL of H2O.

mL to L conversion:

500/1000=.5

For .5L of 0.1M solution, we need 0.1M of solute.

0.1M of solute x 40 grams/Mole= 4 grams NaOH

The solution would be made by dissolving 4 grams NaOH in .5 Liters of H2O

2 Answers By Expert Tutors

Siddharth B. answered • 03/29/20

You needed to use the molarity formula: moles of solute/Liters of solution to find how many moles of solute you needed.

You correctly converted 500 mL to 0.5 L.

Now, we can put the information we already have into the formula.

We want a solution with 0.1 M.

So, we will do 0.1=x/0.5; 0.1*0.5

Solving for x, we find that we need 0.05 moles of solute NaOH.

As you found, the molar mass of NaOH is 40 g. So, we will do 40 g*0.05, which is about 2 g.

John G. answered • 12/05/14

Understanding math via the real world.

Everything looks good except for this part: "To make one mole NaOH solution, dissolve 40 grams NaOH in 500mL of H2O."

To make a one molar solution you want to put one mole of the solute into 1L (1000mL) of H2O. Then you can do your conversion the other way from L to mL. It looks like you included to conversion here, but then didn't use it because you already had your 500mL.

(You should end up with fewer grams of NaOH overall)

Definitions

Solute-the substance being dissolved

Solvent-the substance doing the dissolving (the larger amount)

Solution- a homogeneous mixture of the solute and the solvent

Solution= solvent + solute

Aqueous (aq)= water solution

Tincture= alcohol solution

Amalgam= Mercury solution

Molarity (M)- is the molar concentration of a solution measured in moles of solute per liter of solution.

The molarity definition is based on the volume of the solution, NOT the volume of water.

Vocab. Lesson

Incorrect= The solution is 5.0 Molarity.

Correct= The solution is 5.0 Molar.

Example Problems

Level 1- Given moles and liters

Determine the molarity when 3.0 moles of sucrose are dissolved to make 2.0 liters of solution.

3.0 mol	= X = 1.5M solution
2.0 liters

Level 2- Given Molarity and liters of solution

Determine the number of moles of salt dissolved in 5.0 liters of a 0.50M solution of salt water.

X mol	= 0.5M solution
5.0 liters

cross multiply, X= 2.5 mols

Level 3- Given grams (instead of moles) and liters of solution

Determine the molarity when 117g of NaCl are dissolved to make 0.500 liters of solution.

1st convert to moles, 2nd plug into the molarity equation

117g NaCl( 1mol/58.5g)= 2.00mol NaCl

2.00 mol	= 4.00M solution
0.500 liters

Level 4-Given grams (instead of moles) and milliliters of solution (instead of liters)

Determine the molarity when 55.5g of CaCl2 are dissolved to make 250.mL of solution.

1st convert to moles, 2nd convert to liters, 3rd plug into the molarity equation

55.5g CaCl2( 1mol/111g)= 0.500mol CaCl2

250.ml( 1L/1000mL) =0.250L

0.500 mol	= 2.00M solution
0.250 liters

Past Regents Questions-Follow link to check the answers

Jan 2003-44 What is the molarity of a solution of NaOH if 2 liters of the solution contains 4 moles of NaOH?

(1) 0.5 M (3) 8 M
(2) 2 M (4) 80 M

Jan. 04-41 What is the molarity of a solution containing 20 grams of NaOH in 500 milliliters of solution?

(1) 1 M (2) 2 M (3) 0.04 M (4) 0.5 M

Jan 2002-42 What is the molarity of a solution that contains 0.50 mole of NaOH in 0.50 liter of solution?

(1) 1.0 M (3) 0.25 M
(2) 2.0 M (4) 0.50 M

Aug. 2006-42 How many total moles of KNO3 must be dissolved in water to make 1.5 liters of a 2.0 M solution?

(1) 0.50 mol (2) 2.0 mol (3) 3.0 mol (4) 1.3 mol

Aug 2005-

41 What is the total number of moles of NaCl(s) needed to make 3.0 liters of a 2.0 M NaCl solution?(1) 1.0 mol (3) 6.0 mol

(2) 0.70 mol (4) 8.0 mol

June 2006-

16 Molarity is defined as the(1) moles of solute per kilogram of solvent(2) moles of solute per liter of solution(3) mass of a solution

(4) volume of a solvent

Aug 2008-

15 Which phrase describes the molarity of a solution?(1) liters of solute per mole of solution(2) liters of solution per mole of solution(3) moles of solute per liter of solution

(4) moles of solution per liter of solution

June 2009-

46 Which sample of HCl(aq) contains the greatest number of moles of solute particles?(1) 1.0 L of 2.0 M HCl(aq)(2) 2.0 L of 2.0 M HCl(aq)(3) 3.0 L of 0.50 M HCl(aq)

(4) 4.0 L of 0.50 M HCl(aq)

June 2007-

13 A 3.0 M HCl(aq) solution contains a total of(1) 3.0 grams of HCl per liter of water(2) 3.0 grams of HCl per mole of solution(3) 3.0 moles of HCl per liter of solution

(4) 3.0 moles of HCl per mole of water

June 2010-14 The molarity of an aqueous solution of NaCl is defined as the(1) grams of NaCl per liter of water(2) grams of NaCl per liter of solution(3) moles of NaCl per liter of water

(4) moles of NaCl per liter of solution

Jan 2008-

15 Which unit can be used to express solution concentration?(1) J/mol (3) mol/L

(2) L/mol (4) mol/s

Jan 04-41 What is the Molarity of a solution containing 20 grams of NaOH in 500 milliliters of solution?(1) 1 M (3) 0.04 M

(2) 2 M (4) 0.5 M

Jan 2010-40 What is the molarity of 1.5 liters of an aqueous solution that contains 52 grams of lithium fluoride, LiF, (gram-formula mass =26 grams/mole)?(1) 1.3 M (3) 3.0 M

(2) 2.0 M (4) 0.75 M

on to ppm or Molality

back to Math of Chemistry Links

Chemical Demonstration Videos

In this experiment, we will determine two of the three pKa values for the triprotic acid, phosphoric acid, using acid-base titration. In this neutralization reaction, phosphoric acid reacts with NaOH to form water and the salt, sodium phosphate.

Attach the drop counter to the ring stand, below the burette clamp. Secure the plastic burette so that its tip is just above the drop counter.
Connect the drop counter to the data acquisition system, and make sure the two valves of the plastic burette are both in the closed position.
Place the waste container below the burette and pour a few mL of 0.1 M NaOH into the burette. Open both valves to drain the NaOH into the waste beaker. Then close the valves.
Fill the plastic burette with 25 mL of 0.1 M NaOH. Drain about 5 mL into the waste beaker—enough so that NaOH fills the burette tip. Make sure there are no air bubbles, then close the valves.
Calibrate the drop counter. Replace the waste beaker beneath the burette with a 10-mL graduated cylinder. Then, open the bottom valve on the burette, while keeping the top valve closed. Turn on the data acquisition system and set it to ‘drop counting mode’.
Slowly open the top valve to very slowly release drops, ideally at one drop every 2 s. Allow the drops to empty from the burette until there is 9-10 mL of 0.1 M NaOH in the graduated cylinder.
Close the bottom valve and leave the top valve as is. Read the volume of NaOH in the graduated cylinder to the first decimal place and enter this value in the data acquisition system. Record the value for ‘drops/mL’. Then, discard the NaOH in the graduated cylinder into the aqueous waste beaker.
Calibrate the pH sensor before starting the titration. Connect the pH sensor to the data acquisition system, then select 'Calibrate'. Rinse the bulb of the pH sensor with deionized water before inserting it into the pH 7 buffer. Leave the sensor submerged until the voltage stabilizes, then accept the measurement.
Rinse the bulb with deionized water and insert it into the pH 10 buffer. Allow the voltage to stabilize, then accept the measurement.
Rinse the bulb of the pH sensor again and slide it through the designated slot in the drop counter.
Measure 40 mL of deionized water into a clean 100-mL beaker, then, transfer 1 mL of phosphoric acid into the beaker of water.
Place the beaker on the stir plate under the drop counter. Carefully slide the pH sensor into the beaker.
Add a stir bar to the beaker, and turn the stir setting onto high. Start collecting data on the acquisition device. Then, open the bottom valve on the burette. Note: The drop rate should be about 1 drop every 2 s. After the first drop is released, check to see data are being recorded.
Continue the titration until the pH meter reads pH 12. Then, stop acquiring data and close the valve on the burette. Save your data on a flash drive.
To clean up your workspace, check the pH of all waste solutions using pH paper. Neutralize all acidic aqueous waste with baking soda and all basic waste with citric acid. Add enough of either baking soda or citric acid to the solution until it stops bubbling.
Flush all neutralized solutions down the sink with copious amounts of water.
Wash all glassware.