Ms Ead Stoich packet

In chemistry, the mole is the standard measurement of amount. However, balances DO NOT give readings in moles. Balances give readings in grams. Let us learn how to do these conversions.

Gram to mole conversion

There are steps to converting grams of a substance to moles.

  1. Determine how many grams are given in the problem (place in upper left).
  2. Calculate the molar mass of the substance ( mass of all elements in the compound upper right)
  3. Always use 1 mole of that compound (lower right).
  4. Divide step one by step two( X for the number of moles lower left)
  5. The three steps above can be setup in the following proportion:

Example:

Calculate how many moles are in 17.0 grams of H2O2

17.0 grams are given in the text of the problem. The molar mass is 34.0146 grams/mole, which is calculated using the formula and the atomic weights on a periodic table.

Let’s practice

1) 2.00 grams of H2O

2) 75.57 grams of KBr

3) 100. grams of KClO4

4) 8.76 grams of NaOH

5) 0.750 grams of Na2CO3

Grams to mole conversion practice answers 1-5

1-

2-

3-

4-

5-

Mole to Grams conversion

When substances react, they do so in simple ratios of moles. However, balances give readings in grams. Balances DO NOT give readings in moles. Let us learn how to convert moles to grams.

There are steps to converting moles of a substance to grams:

  1. Determine how many moles are given in the problem (place in lower left).
  2. Calculate the molar mass of the substance( mass of all elements in the compound upper right)
  3. Always use 1 mole of that compound (lower right).
  4. Divide step one by step two( X for the number of grams upper left)
  5. The three steps above can be setup in the following proportion:

Example:

Calculate how many grams are in 0.700 moles of H2O2

0.700 mole x 34.0146 grams/mole = 23.8 grams

Let’s practice

Calculate the grams present in:

1) 0.200 moles of H2S

2) 0.100 moles of KI

3) 1.500 moles of KClO

4) 0.750 moles of NaOH

5) 3.40 x 10¯5moles of Na2CO3

Mole to gram conversion practice answers 1-5

1-

0.200 mole x 34.076 grams/mole = 6.82 gram

2-

0.100 mole x 166.003 grams/mole = 16.6 gram

3-

1.500 mole x 90.551 grams/mole = 135.8 gram

4-

0.750 mole x 39.997 grams/mole = 30.0 gram

5-

3.40 x 10¯5mole x 105.989 grams/mole = 3.60 x 10¯3

Calculating the mass of one molecule, particle or formula unit

When calculating the mass of one molecule, particle or formula unit we do the following:

  1. Calculate the molar mass of the substance
  2. Divide it by Avogadro's Number
  3. The value for Avogadro's Number is 6.022 x 1023mol¯1.

What is the mass of one molecule of H2O?

The molar mass of water is 18.015 g/mol.

Divide the substance's molar mass by Avogadro's Number.

18.015 grams/mol ÷ 6.022 x 1023mol¯1= 2.992 x 10¯23grams

Let’s practice

Calculate the mass (in grams) for one molecule of:

1) H2

2) PCl5

3) UF6

4) F2

5) CH4

Let’s practice

Calculate the mass of one molecule

1) H2

the molar mass of H2is 2.016 g/mol

2.016 g/mol ÷ 6.022 x 1023mol¯1= 3.348 x 10¯24g

2) PCl5

the molar mass of PCl5is 208.239 g/mol

208.239 g/mol ÷ 6.022 x 1023mol¯1= 3.458 x 10¯22g

3) UF6

the molar mass of UF6is 352.019 g/mol

352.019 g/mol ÷ 6.022 x 1023mol¯1= 5.846 x 10¯22g

4) F2

the molar mass of F2is 37.997 g/mol

37.997 g/mol ÷ 6.022 x 1023mol¯1= 6.310 x 10¯23g

5) CH4

the molar mass of CH4is 16.043 g/mol

16.043 g/mol ÷ 6.022 x 1023mol¯1= 2.664 x 10¯23g

More Grams to moles practice

1.Calculate how many moles are in26.0 gram Ca(ClO4)2

2.Calculate how many moles are in32.0 gram O2

3.Calculate how many moles are in34.2 gram NH3

4.Calculate how many moles are in9.00 gram H2SO4

5.Calculate how many moles are in59.3 gram SnF2

6.Calculate how many moles are in0.00500 gram XeO3

7.Calculate how many moles are in10.0 gram SO3

8.Calculate how many moles are in1.00 gram CO2

9.Calculate how many moles are in5.00 gram CaCO3

10.Calculate how many moles are in1.00 gram NaCl

11.Calculate how many moles are in98.9 gram NaI

12.Calculate how many moles are in14.0 gram N2

More mole to Gram practice

  1. Calculate how many grams are in 2.55 mole Cu2CrO4
  2. Calculate how many grams are in 1.500 mole K2SO4
  3. Calculate how many grams are in 3.27 mole O2
  4. Calculate how many grams are in 0.000300 mole AuCl3
  5. Calculate how many grams are in 0.00200 mole Na2SO4
  6. Calculate how many grams are in 0.02 moles of beryllium iodide, BeI2?
  7. Calculate how many grams are in 3.3 moles of potassium sulfide, K2S?
  8. Calculate how many grams are in 238 moles of arsenic?