Question

How many formula units of Nis are contained in a 430. g sample of the compound?

• Use 6.022 x 102 mol 1 for Avogadro's number.
• Report your answer in scientific notation.
• Your answer should have three significant figures​

Answer 1

Answer : The number of formula units of NiS contained are,
`2.85* 10^(24)`

Explanation :

Formula units : It is defined as lowest whole number ratio of ions in an ionic compound.

It is calculate by multiplying the number of moles by Avogadro's number which is
`6.022* 10^(23)`

We are given:

Mass of given sample = 430 g

Molar mass of NiS = 90.76 g/mole

First we have to calculate the moles of NiS.

`\text{Moles of }NiS=\frac{\text{Mass of }NiS}{\text{Molar mass of }NiS}`

`\text{Moles of }NiS=(430g)/(90.76g/mol)=4.74mole`

Now we have to calculate the formula units of NiS.

Number of formula units =
`4.74* 6.022* 10^(23)=2.85* 10^(24)`

Hence, the number of formula units of NiS contained are,
`2.85* 10^(24)`

Answer 2

2.85x10²⁴ NiS formula units

Step-by-step explanation:

The molar mass of the compound must be calculated first. For that, the molar masses of the atoms that form it are added:

mNiS = mNi + mS = 58.69g + 32.07g = 90.76 g / mol

Now the molar mass can be related to the amount of formula units there will be of the compound. In a mole there are 6,022x10²³ formula units, and we know that it also occupies a mass of 90.76 g, so the mathematical calculation can be performed.

90.76 g NiS _____ 6.022x10²³ formula units

430.0 g NiS _____ X = 2.8531x10²⁴ formula units

Calculation: 430.0 g x 6.022x10²³ x 90.76 g = 2.8531x10²⁴units formula ≅ 2.85x10²⁴

Using scientific notation and using three significant figures to express the result, the answer is that in 430.0g of NiS there are 2.85x1024 formula units of the compound.