3.7.2024 - Student Review 3

What are the 2 most common mistakes Scholars make when calculating % composition?

• The subscript is not properly multiplied

• The superscript is not properly divided

• The decimal is not multiplied by 100 to turn your answer into a %

• The decimal is not divided by 100 to turn your answer into a %

STOP VIDEO AT 3:45

Using the information we have just been given, let's find the % composition of Oxygen in N₃O_. First we need to find the molar mass of N₃O.

• 90 g/mol

• 62 g/mol

• 58 g/mol

• 18 g/mol

STOP VIDEO AT 3:45

Now that we have figured the molar mass of N₃O, we can now calculate the % composition of Oxygen in our compound. Using the given formula, plug the numbers in (don't forget to multiply by 100). The molar mass of Oxygen divided by the molar mass of the whole compound (N3O).

• 0.27586 %

• 28 %

• 72 %

• .72413 %

CONTINUE VIDEO UNTIL THE END.

Using the information we have just been given, let's find the % composition of Na in Na₃Cl₃. First we need to find the molar mass of Na₃Cl₃.

• 59 g/mol

• 35 g/mol

• 177 g/mol

• 23 g/mol

CONTINUE VIDEO UNTIL THE END.

Now that we have figured the molar mass of Na₃Cl_3, we can now calculate the % composition of Sodium in our compound. Using the given formula, plug the numbers in (don't forget to multiply by 100). The molar mass of Sodium divided by the molar mass of the whole compound (Na₃Cl₃).

• 50 %

• 0.610 %

• 40 %

• 61 %

Now try one on your own...

Find the % composition of Hydrogen in H₃O, heavy water (used in the fracking process of natural gas). Don't forget the 2 most common mistakes when calculating the % composition of a compound.

• 11 %

• 84 %

• 89 %

• 16 %

STOP VIDEO AT THE 1:00 MINUTE MARK

Our goal is to find the mass in grams of 3.65. moles of Mg?

For now, let's work the problem step by step so, we need to find the mass of 1 mole of Mg. To find this we look it up on the Periodic Table (PT). After you have answer this, begin the video again.

• 24.305

• 9.0122

• 22.990

• 40.078

STOP THE VIDEO AT THE 3:00 MINUTE MARK

If one mole of Mg has 24.305 g, how many would 2 moles of Mg have? And then, how many would 3.65 moles of Mg have?

Restart the video after answering this question.

• 48.61 g & 88.71 g

• 24.305 g & 88.71 g

• 24.305 g & 48.61 g

• The answers are not shown here.

STOP THE VIDEO AT THE 5:00 MARK.

Decide which conversion factor you will use (see picture to the left.). Remember the units must cancel out (what goes up, must come down).

Once you have answered the question, begin the video

• A

• B

STOP THE VIDEO AT THE 5:55 MARK.

According to the picture to the left, which is the correct set up for converting moles to grams? (remember that units must cancel)

Begin the video once you have answered the question.

• A

• B