chem exam 2 - unit 6 the mole

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14 Terms

1
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1 mole

6.023 × 10^ 23

  • Avogadro’s number

  • unit to measure chemical quantities and number of atoms/molecules

2
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finding molar mass

atomic mass = molar mass

ex: atomic mass of Carbon (C) = 12.01 amu → molar mass = 12.01 g/mol

3
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moles to particles

Mole x 6.023 × 10^ 23/1 mole = particles

4
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particles to moles

particles x 1 mole.6.023 × 10^ 23 = mole

<p>particles x 1 mole.6.023 × 10^ 23 = mole</p>
5
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mole to mass

mole x molar mass/1 mole = mass

<p>mole x molar mass/1 mole = mass</p>
6
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mass to mole

mass x 1 mole/molar mass = mole

<p>mass x 1 mole/molar mass = mole</p>
7
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volume (L) to moles OR moles to volume (L)

V to M = volume x 1mole/22.4 L = moles

OR

M to V = moles x 22.4 L/1 mole = volume

8
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mass to particles

mass x 6.023 × 10^ 23/molar mass = atoms

<p>mass x 6.023 × 10^ 23/molar mass = atoms </p>
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particles to mass

atoms x molar mass/6.023×10^ 23 atoma = mass

10
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how to find molar mass of molecules

ex: C6H6

  1. multiply the subscript values of each element by their own molar mass and add products together

  • 6×12 + 6×1 = 78 molar mass

  • 78 g of C6H6 = 1 mol

11
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how to find molar mass of formula units

sum of the molar mass of the constituent atoms

ex: CaCO3:

1 Ca = 40 g

1 C = 12 g

3 O = 3(16) g = 48 g

40+12+48 = 100 g = 1 mole = formula mass of CaCO3

12
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how to find amount of formula units in a compound

Step 1: Find the molar mass of MgCl₂

Mg = 24.305 g/mol
Cl = 35.45 g/mol × 2 = 70.90 g/mol

Molar mass of MgCl₂=24.305+70.90=95.205 g/mol

🔹 Step 2: Convert grams to moles moles of MgCl₂= 300 g/95.205 g/mol≈3.15 mol

🔹 Step 3: Convert moles to formula units

Use Avogadro’s number:

1 mol=6.022×1023 formula units

formula units of MgCl₂=3.15 mol×6.022×10^23≈1.90×10^24


Final Answer: 1.90×10^24 formula units of MgCl₂

13
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percent composition

“each element’s mass in a molecule compared to the total mass of the compound”

percent composition = mass of element/mass of molecule x 100

ex: percent comp of carbon = 12g/16g x 100 = 75%

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empirical formula

rations of elements present in the compound (but NOT the actual number of atoms in the molecule)

  • subscripts are the smallest whole numbers that indicate the ratio of elements

  • ex: C20H12

empirical formula = C5H3