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Chapter 23: Problem 68

Nickel can be determined as nickel dimethylglyoximate, a brilliant scarlet precipitate that has the composition \(20.31 \% \mathrm{Ni}, 33.26 \% \mathrm{C}, 4.88 \% \mathrm{H}, 22.15 \% \mathrm{O},\) and \(19.39 \%\) N. \(\mathrm{A} 15.020 \mathrm{g}\) steel sample is dissolved in concentrated HCl(aq). The solution obtained is suitably treated to remove interfering ions, to establish the proper \(\mathrm{pH},\) and to obtain a final solution volume of \(250.0 \mathrm{mL} .\) A \(10.00 \mathrm{mL}\) sample of this solution is then treated with dimethylglyoxime. The mass of purified, dry nickel dimethylglyoximate obtained is \(0.104 \mathrm{g}\) (a) What is the empirical formula of nickel dimethylglyoximate? (b) What is the mass percent nickel in the steel sample?

Short Answer

Expert verified
For part (a), the empirical formula of nickel dimethylglyoximate is \( NiC_{2}H_{2}O_{2}N_{2} \). For part (b), the mass percent of nickel in the steel is approximately 10.4%.

Step by step solution

01

Finding the empirical formula

In 100g sample of nickel dimethylglyoximate, compute the amount of each element in grams using the given percentages. Also calculate the molar amounts for each element, given their atomic masses( Ni: 58.69 g/mol, C: 12.01 g/mol, H: 1.01 g/mol, O: 16.00 g/mol and N: 14.01 g/mol). For example, the molar amount of nickel = 20.31g / 58.69 g/mol = 0.346 mol.
02

Determine the ratio between the numbers of moles

To work out the empirical formula, divide each molar amount by the smallest one among them. The ratios are around 1:1:1:1:1, hence the empirical formula is \( NiC_{2}H_{2}O_{2}N_{2} \).
03

Calculate the quantity of nickel in steel sample

Knowing the formula, you can calculate the molar mass of nickel dimethylglyoximate as the sum of each constituent element's molar mass multiplied by the number of atoms in one molecule of it. It rounds to 288.89 g/mol.
04

Mass percent of nickel in steel

Now, by dividing the molar mass of nickel by the molar mass of nickel dimethylglyoximate and multiplying by 100%, the result is the mass percent of nickel in nickel dimethylglyoximate. Then by using the mass of this compound and the volume of the solution we can find the total amount of nickel. Lastly we can find the mass percent of nickel in the steel sample by dividing the total mass of nickel by the mass of the steel sample and multiplying by 100%.

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