Dimensional Analysis

Dimensional Analysis

Practice your knowledge of dimensional analysis.

Conversion factors that we use when...

• Converting between moles and particles:  $1\ mol\ =\ 6.02\times10^{23}$  

• Converting between moles and grams:  $1\ mol\ =\ molar\ mass\ \left(g\right)$  

• NOTE: You can use BOTH conversion factors to convert between particles and grams

Multiple Choice

What conversion factor would you use to determine how many moles are in 5.8 grams of water (H₂O)?

• 1 mol = 6.02 x 10²³ particles

• 1 mol = molar mass (g)

• 6.02 x 10²³ particles = molar mass (g)

• None of the above

Multiple Choice

What conversion factor would you use to determine how many moles are in 78 atoms of Na?

• 1 mol = molar mass

• 1 mol = 1 mol

• 1 mol = 6.02 x 10²³ particles

• 1 mol = 62 x 10²³ particles

Converting particles to grams

• particles --> moles --> grams

•  $given\ \times\frac{mol}{given\ unit}\times\frac{grams}{mol}$  

Converting grams to particles

• grams --> moles --> particles

•  $given\ \left(g\right)\times\frac{moles}{g}\times\frac{particles}{moles}$  

Multiple Choice

How will you determine the amount of grams in 4.5 atoms of Na?

• Convert 4.5 atoms to grams (molar mass), then to moles (avogadro's number)

• Convert 4.5 atoms to grams (molar mass), then to moles (avogadro's number)

• Convert 4.5 atoms to moles (avogadro's number), then to grams (molar mass)

• Convert 4.5 atoms to particles, then to grams

Multiple Choice

How would you determine the amount of particles in 9.2 grams of MgO₂?

• Convert 9.2 grams to moles only.

• Convert 9.2 atoms to moles (avogadro's number), then to grams (molar mass)

• Convert 9.2 grams to particles (avogadro's number), then to moles (molar mass)

• Convert 9.2 grams to moles (molar mass), then to particles (avogadro's number)

Multiple Choice

Which of the following shows the correct set up to convert from moles to grams?

• $mol\times\frac{grams}{mol}$

• $mol\times\frac{mol}{grams}$

• $grams\times\frac{mol}{grams}$

• None of the above

Setting up dimensional analysis:

• particles to moles:

   $given\ units\times\frac{mol}{given\ units}$  

• moles to particles:  $moles\times\frac{particles}{moles}$  

• grams to moles:  $g\times\frac{moles}{molar\ mass\ \left(g\right)}$  

• moles to grams:  $moles\times\frac{molar\ mass\ \left(g\right)}{moles}$  

Multiple Choice

How will you determine the amount of grams in 4.5 atoms of Na?

• Convert 4.5 atoms to grams (molar mass), then to moles (avogadro's number)

• Convert 4.5 atoms to grams (molar mass), then to moles (avogadro's number)

• Convert 4.5 atoms to moles (avogadro's number), then to grams (molar mass)

• Convert 4.5 atoms to particles, then to grams

Multiple Choice

Determine how many molecules of water are in 4.5 g of water. What should be used to complete the dimensional analysis set up below?

 $4.5\ g\ H_2O\ \times\frac{1\ mol}{18.02\ g\ H_2O}\times\frac{?\ molecules}{1\ mol}$  

• Molar mass of water

• Avogadro's Number (6.02 x 10^23)

• Atomic mass of hydrogen

• 1 molecule

Multiple Choice

Calculate how many grams are in 3.4 moles of water by completing the dimensional analysis set up below:

 $?\ \times\frac{18.02\ g}{1\ mol}$  

• 18.02 moles

• 3.4 moles

• 3.4 grams

• 18.02 grams

Multiple Choice

Determine how many grams of water are in 34 molecules of water by finishing the dimensional analysis set up below:

 $34\ molecules\ \times\frac{1\ mol}{6.02\times10^{23}\ molecules}\times\frac{18.02\ ?}{1\ mol}$  

• moles

• molecules

• grams

• atoms

Multiple Choice

When converting from particles to grams, how should the dimensional analysis be set up?

• $particles\ \times\frac{particles}{mol}\times\frac{gram}{mol}$

• $particles\ \times\frac{mol}{particles}\times\frac{mol}{grams}$

• $particles\ \times\frac{mol}{particles}\times\frac{gram}{mol}$

• $grams\ \times\frac{mol}{particles}\times\frac{particles}{mol}$

Calculating Molar Mass

• Write each individual element

• Determine the number of moles for each element in the compound

• Multiply the number of moles of the element by its atomic mass to find the total mass for each element

• Add each total mass together to get molar mass

Calculate molar mass of water (H₂O)

• H: 2 moles x 1.01 g/mol = 2.02 g H

• O: 1 mol x 16 g/mol = 16 g O

• 2.02 g + 16 g = 18.02 g of H₂O

• Molar mass = 18.02 g

Multiple Choice

Calculate the molar mass of MgO₂.

• 56.3 g

• 65.4 g

• 70 g

• 123 g

Multiple Choice

To find the molar mass of NaCl, what should you multiply the atomic mass of Na by?

• 4 mol

• 3 mol

• 2 mol

• 1 mol

Multiple Choice

Calculate the molar mass of CuCl₂.

• 34.45 g

• 204.1 g

• 150.2 g

• 134.4 g

Multiple Choice

To find the molar mass of CaCO₃, what should you do to find the total mass of oxygen (O).

• 1 mol x 16 g/mol

• 3 mol x 40 g/mol

• 3 mol x 16 g/mol

• 1 mol x 40 g/mol

Multiple Choice

Calculate the molar mass of K₂SO₄.

• 174.2 g

• 147.2 g

• 472.1 g

• 217.4 g