How many formula units (f.un.) are in [tex]$35.0 g KNO_3$[/tex]?
([tex]$1 mol KNO_3=101.11 g$[/tex])
([tex]$1 mol KNO_3=6.02 \times 10^{23}$[/tex] formula units)
[?] [tex]$\times 10^{[?]} \text { f.un. } KNO_3$[/tex]
Enter the coefficient in the green box and the exponent in the yellow box.
Answer (2)
Calculate the number of moles of K N O 3 : m o l es = \t 101.11 g / m o l 35.0 g = 0.34616 m o l .
Calculate the number of formula units: f or m u l a _ u ni t s = 0.34616 m o l × 6.02 × 1 0 23 f . u n ./ m o l = 2.08388 × 1 0 23 f . u n .
Express the answer in scientific notation: 2.08388 × 1 0 23 f . u n .
The coefficient is 2.08 and the exponent is 23 , so the final answer is 2.08 × 1 0 23 .
Explanation
Problem Analysis We are given the mass of K N O 3 as 35.0 g , the molar mass of K N O 3 as 101.11 g / m o l , and the number of formula units per mole as 6.02 \t × 1 0 23 . Our goal is to find the number of formula units in 35.0 g of K N O 3 and express the answer in scientific notation.
Calculating Moles First, we need to calculate the number of moles of K N O 3 in 35.0 g . We can use the formula: m o l es = m o l a r _ ma ss ma ss Substituting the given values, we get: m o l es = 101.11 g / m o l 35.0 g = 0.34616 m o l
Calculating Formula Units Next, we calculate the number of formula units by multiplying the number of moles by Avogadro's number: f or m u l a _ u ni t s = m o l es × 6.02 × 1 0 23 Substituting the calculated value of moles, we get: f or m u l a _ u ni t s = 0.34616 m o l × 6.02 × 1 0 23 f . u n ./ m o l = 2.08388 × 1 0 23 f . u n .
Final Answer Finally, we express the answer in scientific notation in the form [ ?] × 1 0 [ ?] .
2.08388 × 1 0 23 f . u n . So the coefficient is 2.08 and the exponent is 23 .
Examples
Understanding how to convert mass to the number of formula units is crucial in chemistry for preparing solutions and understanding reaction stoichiometry. For example, if you need to prepare a specific concentration of a potassium nitrate solution for a plant fertilizer, you need to know exactly how many formula units of K N O 3 are present in a given mass to achieve the desired concentration. This ensures the plants receive the correct amount of nutrients for optimal growth.
There are approximately 2.08 \times 10^{23} formula units in 35.0 g of KNO3. This is calculated by first finding the number of moles from the mass and then converting moles to formula units using Avogadro's number. The coefficient is 2.08 and the exponent is 23.
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