Question

To measure the amount of nickel in some industrial waste fluid, an analytical chemist adds 0.460 M sodium hydroxide (NaOH) solution to a 23.0 g sample of the fluid and collects the solid nickel II) hydroxide (Ni(OH)2) product. When no more Ni (OH) is produced, he filters, washes and weighs it, and finds that 206. mg has been produced The balanced chemical equation for the reaction is: Ni2+(aq) + 2NaOH(aq) Ni (OH)2(s) + 2Na+ (aq) ■ precipitation x 10 acid-base What kind of reaction is this? redox If you said this was a precipitation reaction, enter the chemical formula of the precipitate If you said this was an acid-base reaction, enter the chemical formula of the reactant that is acting as the base If you said this was a redox reaction, enter the chemical symbol of the element that is oxidized Calculate the mass percent of Ni in the sample. Be sure your answer has 3 significant digits 0%

Answer 1

it is a precipitation reaction

the chemical formula of precipitate = Ni(OH)₂

mass of Ni(OH)2 produced = 206 mg

moles of Ni(OH)2 produced = mass / molar mass = 206 /   92.708 = 2.222 mmoles

since 1 mole of Ni(OH)2 contain 1 mole of Ni

so moles of Ni present = 2.222 mmoles

mass of Ni present = mole * atomic mass = 2.222* 58.69 = 130.41 mg

mass of Ni present in sample = 130.41 mg = 0.13041g

so mass percentage of Ni present =(mass of Ni in sample / total mass of sample ) *100

mass percentage of Ni present =( 0.13041 / 23 ) *100 = 0.567 %

so

mass percentage of Ni in the sample = 0.567 %