If 25cm^3 of NaOH solution containing 4.0g per litre of solution neutralised 50cm^3 of a monobasic acid,HX containing 1.8g of acid.Calculate the R.F.M of the acid. I got the molarity of NaOH to be 0.1,then i got stuck.plz help
RFM...relative formula mass
Ma*Va=Mb*Vb
Vb=.025 Va=.050
Ma=Mb* .5
Mb= 4/40=.1 so
Ma=.05
but Molarity acid= mass/RFM*Va= 1.8/RFM*.060=36/RFM
RFM=36/.05=720 check my math.
To calculate the relative formula mass (RFM) of the acid (HX), you need to use stoichiometry based on the volume and concentration of the NaOH solution used.
Here are the steps to calculate the RFM of the acid:
1. Calculate the number of moles of NaOH used:
Since you have the concentration of NaOH solution and the volume used, you can calculate the number of moles of NaOH used.
Molarity = moles/volume
0.1 M = n/0.025 L
n = 0.1 * 0.025
n = 0.0025 moles
2. Determine the stoichiometry of the reaction between NaOH and HX:
Based on the balanced chemical equation, we know that NaOH reacts with HX in a 1:1 ratio.
3. Calculate the number of moles of acid (HX) from the reaction:
Since NaOH and HX react in a 1:1 ratio, the number of moles of acid (HX) will be the same as the number of moles of NaOH used.
Therefore, the number of moles of HX = 0.0025 moles.
4. Calculate the mass of HX used:
Mass = number of moles x molar mass
Mass = 0.0025 moles x 1.8 g/mole
Mass = 0.0045 grams
5. Finally, calculate the RFM of the acid (HX):
RFM = mass/number of moles
RFM = 0.0045 grams/0.0025 moles
RFM = 1.8 g/mole
Therefore, the RFM of the acid (HX) is 1.8 g/mol.
To solve this problem, you need to use the concept of molarity and the balanced chemical equation for the neutralization reaction between NaOH and HX.
First, let's find the moles of NaOH used in the reaction:
Molarity is defined as the number of moles of solute per liter of solution. Since we know that the molarity of NaOH is 0.1 M (or 0.1 mol/L), and we have 25 cm^3 of NaOH solution, we need to convert the volume to liters:
25 cm^3 = 25/1000 L = 0.025 L
Now we can calculate the moles of NaOH used:
Moles of NaOH = Molarity × Volume
Moles of NaOH = 0.1 mol/L × 0.025 L = 0.0025 mol
According to the balanced chemical equation, 1 mole of NaOH reacts with 1 mole of HX. Therefore, the moles of HX used in the reaction is also 0.0025 mol.
Next, we need to find the mass of HX used in the reaction:
We know that the solution contains 4.0 g of NaOH per liter of solution, which means that there are 4.0 g of NaOH in 1000 mL of solution. Since we used 50 cm^3 of the solution, which is 50/1000 L, the mass of NaOH used is:
Mass of NaOH = (4.0 g/1000 mL) × 50 mL = 0.2 g
Since the reaction is a 1:1 ratio, the moles of NaOH used is equal to the moles of HX used, which is 0.0025 mol.
Now, we can find the molar mass (RFM) of HX using the given mass of acid:
Molar mass of HX = Mass of acid / Moles of HX
Molar mass of HX = 1.8 g / 0.0025 mol = 720 g/mol
Therefore, the relative formula mass (RFM) of the acid HX is 720 g/mol.
Note: The given molarity of NaOH is correct, and you correctly calculated the moles of NaOH used. You were on the right track, just missing the step to equate the moles of NaOH to the moles of the acid HX and then using the mass of the acid to calculate the molar mass.