Introduction
Mohr salt is a double swab containing ferrous sulphate and ammonium sulphate in equimolar quantities. Hence, when these two mariners are mixed in the rate of their molecular millions and also a hot logged result prepared, filtered and the hot filtrate cooled, light blue or green chargers of Mohr swab (octahedral in shape) are attained.
Mohr’s swab is prepared by dissolving an equimolar admixture of doused FeSO4.7H2Oand ammonium sulphate in the water containing a little sulphuric acid. Take a clean 250 ml teacup; transfer 7 g of FeSO4 and 3.5 g of ammonium sulphate chargers to it. Add 2.3 ml of dilute sulphuric acid to help hydrolysis. 200 ml of water is boiled for 5 twinkles. Add boiling hot water to the contents in small amounts. Now stir until mariners have fully dissolved. Sludge it and toast the filtrate in a demitasse dish till it concentrates to the Crystallisation Point. Place the demitasse dish for cooling for about 12 hours and collect the chargers of Mohr’s swab using the sludge paper.
Compared the attained Mohr’s swab and original Mohr’s swab, using chemical styles similar as permanganometry and dichrometry system. Compare the attained Mohr’s swab and original Mohr’s swab using physical styles similar to FTIR spectroscopy, UV-Visible spectroscopy and melting point determination.
Mohr’s salt is an inorganic compound which is a double salt with the formula (NH4)2Fe(SO4)2(H2O)6. It is a common laboratory reagent with IUPAC name ammonium iron(II) sulphate. Mohr’s salt is named after German Chemist Karl Fredrich Mohr.
Aim:
To prepare double salt ferrous ammonium sulphate or Mohr’s salt.
Theory:
A double salt is a salt that contains an equimolar mixture of two salts with different cations but the same anion. Mohr’s salt is a double salt. So, when equimolar proportions of ferrous sulphate and ammonium sulphate are mixed to form a solution and then crystallised, we get crystals of ferrous ammonium salt or Mohr’s salt. The reaction can be shown as follows –
FeSO4 + (NH4)2SO4 + 6H2O 🡪 FeSO4.(NH4)2SO4.6H2O
Ferrous Ammonium Water Ferrous Ammonium Sulphate
Sulphate Sulphate or Mohr’s Salt
Iron(II) cations can undergo hydrolysis, therefore to prevent it while preparing their aqueous solution, a small amount of dilute sulphuric acid is added.
Requirements:
Beaker, conical flask, trough, glass rod, tripod stand, funnel, wire gauze, weighing machine, ferrous sulphate, ammonium sulphate, distilled water, dilute sulphuric acid.
Procedure:
Weigh 3.5 g of ferrous sulphate and keep it separately.
Weigh 1.7 g of ammonium sulphate and keep it separately.
Take a conical flask of 50ml and wash it with distilled water.
Now take 5ml of distilled water in the conical flask and add earlier weighed quantities of ferrous sulphate and ammonium sulphate.
Add 0.5ml of dilute sulphuric acid in the conical flask to prevent hydrolysis of iron cations.
Now gently warm the mixture (solution) to get a clear solution.
Filter the solution.
Concentrate the solution(filtrate) by heating it till crystallisation point is reached.
Stir the solution occasionally while heating.
Allow the mixture to cool to room temperature.
After cooling the solution, you will get crystals of ferrous ammonium sulphate (green colored).
Decant the mother liquor and separate the crystals.
Now wash the crystals with water and alcohol mixture (1:1).
Dry the crystals and note down the yield of the product.
Observation Table:
Result:
Yield of Mohr’s salt or ferrous ammonium sulphate is ________g.
Precautions:
For crystallisation, the solution should cool down slowly.
Do not disturb the solution while cooling during crystallisation.
Don’t overheat the solution for crystallisation. As it may change ferrous ions into ferric ions which will change stoichiometry of the solution.
Mohr’s salt is largely used in analytical chemistry. Inhalation of Mohr’s salt causes irritation in the nose and throat. Over exposure of it can cause diarrhoea as well. So, while experimenting you need to be very careful.
This was all about preparation of Mohr’s salt, if you are looking for Mohr’s salt titrations which are important lab experiments of Class XII chemistry then you can go through the page ‘Mohr’s salt titration against potassium permanganate’. Many such articles are available on Vedantu to help you. If you also want to get NCERT Solutions of Chemistry Class XII then register yourself on Vedantu or download Vedantu learning app for class 6-10, IIT-JEE and NEET.
FAQs on Preparation of Mohr’s Salt or Ferrous Ammonium Sulphate
1. What is the Titration Method?
Estimation of oxalic acid by Permanganometry A given weight of set and original Mohr’s mariners are taken in 100 ml separate standard steins.10 ml of dilute sulphuric acid is added to both during the makeup. The result is also shaken well to make it homogeneous. About 20 ml of each result is also collected in the conical beaker Independently. The burette is filled with KMnO4 results. Also, these results are titrated against KMnO4 results till the pale pink colour appears. Repeated to get the accordant values for both the results.
Estimation of ferrous iron by Dichrometry A given weight of set and original Mohr’s swabs are taken in a 100 ml separate standard beaker.10 ml of dilute H2SO4 is added to both during the make up and the result is also shaken well to make it homogeneous. About 20 ml of each result is also collected in the conical beaker independently. Add 50 ml of 4 N H2SO4 and0.5 ml of N-Phenyl anthranilic acid. The burette is filled with K2Cr2O7. Also, these results are titrated against K2Cr2O7 till the green colour to violet red. Repeated to get the accordant values for both the results.
2. Describe the Procedure of Double Salt: Potassium Aluminium Sulphate (Potash Alum)?
Take 10 mL of distilled water in a 50 mL teacup and heat it to about 40 °C.
Dissolve6.6 g of aluminium sulphate in it and add about0.4 mL of dilute sulphuric acid.
Weigh 2.4 g of pulverised potassium sulphate and transfer to the below result.
Toast the result with constant shifting till potassium sulphate dissolved fully.
Allow the result to cool to room temperature sluggishly.
On cooling, white chargers of potash alum separate out.
Decant the mama liquor and wash the chargers by gently shaking with 11 cold water and alcohol admixtures.
Filter the chargers, dry these between the crowds of a sludge paper and note the yield.
3. Describe the Procedure of Double Salt: Ferrous Aluminium Sulphate?
Dissolve 3.5 g of ferrous sulphate and1.7 g of ammonium sulphate (counted independently), in 5 mL of distilled water contained in a 50 ml conical beaker by heating. Add about 0.5 mL of dilute sulphuric acid to the beaker and concentrate the result by hitting till the crystallisation point is reached. Allow the admixture to cool to room temperature sluggishly. On cooling, light green chargers of ferrous ammonium sulphate separates out. Decant the mama liquor and wash the chargers by shaking with veritably small quantities of 11 cold water and alcohol admixture to remove sticking mama liquor. Separate the chargers by filtration marshland with alcohol, dry between the crowds of a sludge paper and record the yield.
4. What is the Use of Ferrous Ammonium Sulphate (Mohr Salt)?
This double swab of ferrous sulphate and ammonium sulphate is a laboratory reagent. Ferrous ammonium sulphate, not ferrous ammonium sulphate as it's occasionally pertained to, dissolves in water and possesses an octahedral molecular figure when formed as an aqua complex. It derives its name from the German druggist Karl Friedrich Mohr, a 19th-century colonist in the development of titration methodology. Mohr’s swab is used in logical chemistry as the preferred source of ferrous ions due to the solid’s extended shelf life and resistance to oxidation. Sulfuric acid is frequently added to results using ferrous ammonium sulphate in order to reduce the oxidation of the ferric iron. The most common system of medication for ferrous ammonium sulphate is to dissolve an equimolar admixture of doused ferrous sulphate and ammonium sulphate in water with a small quantum of sulfuric acid, also subjugating the combined result to crystallisation. Ferrous ammonium sulphate is generally composed of light green chargers in solid form.
5. Why is Dil. H2SO4 used in KMnO4 Titration?
Potassium Permanganate may be a protean and important oxidant that will be wont to determine numerous substances by direct or circular titration. A unique advantage of permanganate of potash is that it is its own index. Titrations with Permanganate must be administered in the strong acid results. Sulfuric Acid is usually used for this purpose because aqua fortis and acid can share in contending oxidation-reduction responses, reducing the delicacy of the titration.
Potassium Permanganate isn't considered a primary standard substance and results of it are generally formalised with arsenic or Sodium Oxalate, both of which are available from the National Institute of Norms and Technology (NIST).
The Arsenious Acid within the first response is produced by neutralisation of the alkaline result wont to dissolve the arsenic. The ethanedioic acid within the alternate equation is made when the Sodium Oxalate is dissolved within the acid result before the titration is begun. Since the Manganese is reduced from the 7 to the 2 (Manganous) state, the primary weight of permanganate of potash is one-fifth of its relative molecular mass.
