Result and Discussion: An amount 2.910g of Ni(NO 3 ) 2 ?6H 2 O was dissolved in

Question

Result and Discussion:

            An amount 2.910g of Ni(NO3)2?6H2O was dissolved in 15ml of water, and 2g of KSCN in 10ml of water. The color of Ni(NO3)2?6H2O was light green, and the color of KSCN was clean colorless solution. After both of the solid dissolved completely, Ni(NO3)2?6H2O solution was pour into other beaker. The color of mixture changed to dark green. The mixture was stirring then and added 1.50ml of ethylenediamine. The color of mixture became light. By pH meter and use 2-aminoethanol which made the pH of mixture in 9.5. after that, small amount of citric acid which made the pH of mixture decreased to 8. The color of mixture changed to purple without precipitate appear. After that, pour the mixture in two different vials equally, and marked them A, B samples. An amount 3ml of benzene was added to sample A and both of samples kept in the hood for two weeks. After that, the crystals were created in both sample, then isolated them by using Buchner funnel and wish crystals with absolute ethanol, also draw air out of the crystals. After the crystals of both samples were dry, place them in watch glass and put into oven for an hour at 130 oC. Then, remove watch glasses out of the oven and kept cool in room tepm. And weight them. Mass of crystals of sample A was 0.301g and sample B was 0.250g. The melting point of sample A is 198 and sample B is 215.

Calculate the mass lost from your [Ni(en)_2(NCS)_2] times C_6H_6 sample during heating. Assuming that the entire mass loss is due to benzene and that all of the benzene was driven out of the structure, calculate the moles of C_6H_6 and of [Ni(en)_2(NCS)_2] in the inclusion compound. Based on these results, what is the formula of this compound? (In other words, what is x in the formula written above?)

Explanation / Answer

Sample A is [Ni (en)2 (NCS)2] xC6H6.

Sample B is [Ni (en)2 (NCS)2]

Molar mass of [Ni (en)2 (NCS)2] = 296.9 g/mol

Mass of sample B, that is [Ni (en)2 (NCS)2] = 0.250 g

Moles of [Ni (en)2 (NCS)2] = 0.250 / 295.1 = 8.47 * 10-4 moles.

Difference in mass of sample A and sample B = 0.301g - 0.205g = 0.051 g (due to loss of C6H6)

Molar mass of C6H6 = 78 g / mol.

Moles of C6H6 lost = 0.051 g / 78 g/mol = 6.54 * 10-4 moles

Since moles of [Ni (en)2 (NCS)2] and C6H6 are lmost same their ratio must be 1 : 1.

Thus formula of compound should be [Ni (en)2 (NCS)2].C6H6

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