How Many Molecules Are There in a Gram of Chemical?

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The mole is the unit of measure in chemistry. Weighing scales, on the other hand, do not provide molecular readings. Scales typically display results in grams, but some can also display ounces

The issue arises from the fact that moles are used for comparisons, but grams are what we actually get from balances, so we have to use grams anyway.

Changing from grams to moles requires three simple operations.

  1. Find the weight in grams given the problem
  2. Deduce the substance's molar mass.
  3. The ratio of Step 1 to Step 2

The use of a calculator and a periodic table will be required.

The method of resolution can also be expressed in terms of the following ratio and proportion:

particles of the
substance   density of the molecule
mass in grams of substance –––––––––––  =  ––––––––––––––– particles that make up the
substance   one mol

In this example, we'll use x to represent an unknown value for the number of moles of the substance (shown in the lower left). When converting from moles to grams, the same ratio is used, so the "x" will be in the top left corner of the chart.

This is merely a mathematical symbol, as this ratio does not exist in reality. Symbolic equations are used to solve real-world problems by substituting the appropriate numbers and units for those in the symbol. Be careful not to put numbers on the unknowable, either. So let there be only an "x" to indicate this. Solving the problem of proportion and cancellation of units should lead naturally to the development of the correct unit.

Conversion Example #1: 25 conversion of moles to grams of KMnO4


In the first stage, 1)

The amount of mass in grams will be revealed by the equation. Find the gram symbol. How many grams will be the number before it. Grams can be shortened to g, or just g, or to gm.

The gram total could be written after the unit in a problem, but I doubt that would happen very often in a high school setting.

For this problem, we are given 25 0 grams

Second, follow these steps:

The molar mass of the substance is crucial. If you are unsure how to calculate a molar mass, please review the lessons on molecular weight and molar mass.

For your reference, KMnO4 has a molar mass of 158. 034 g/mole Make sure you know the molar mass of KMnO4 by doing the math now.

Third Step:

You can solve this problem by dividing the grams required by the problem by the molar mass of the substance.

25.0 g     –––––––––  =  0.158 mol 158.034 g/mol    

Given this, the correct response is zero. Since 25 is a rounding off error, 158 mole has been rounded to three significant figures. The least number of significant digits in the problem was found for the 0 value.

4) If you arranged this problem in the same proportion as the one up top, you'd get this:

25.0 g   158.034 g ––––––  =  ––––––– x   1 mol

5. Use cross-multiplication and division to find the missing number.

(25 0 g) (1 mol) = (x) (158 034 g)

x = 0 158 mol

Second Illustration: Determine the number of moles in 17 Insignificant amounts of H2O2


1) 17 The problem specifies a mass of zero grams.

(2) The molar mass is 34 The formula and atomic weights from a periodic table yield a molecular weight of 0.146 g/mole. In order to ensure that you have mastered molar mass calculations, you may wish to determine this value.

Third, convert the problem's gram weight to moles using the molar mass of the substance:

17.0 g     ––––––––––––  =  0.500 mol 34.0146 g/mol    

This result, based on the 17 0

4. This issue can also be posed as a proportion:

17.0 g   34.0146 g –––––  =  –––––––– x   1 mol

Molecular weight of a solution of 2 0.01 g of water


2.00 g     –––––––––––  =  three significant figures = 0.111 mol 18.015 g/mol    

4. Determine the number of moles in 100 grams of KClO4 (notice the use of a decimal point with a value of 100) This is done to emphasize the significance of the two zeroes, which, together with the one digit, yields three significant figures in 100. )


Modifying the Ratio and Proportion Only

100. g   138.547 g –––––  =  –––––––– x   1 mol

(100 g) (1 mol) = (x) (138 547 g)

x = 0 To three significant figures, 722 mol

Converting 8 is Example #5 Converting between grams and moles of NaOH: 76

8.76 g   39.97 g –––––  =  –––––––– x   1 mol

(8 76 g) (1 mol) = (x) (39 97 g)

x = [(8 76 g) (1 mol)] / 39 97 g

x = 0 To three significant figures, 219 mol

Here's a quick molecular weight calculation example: Cobalt(II) sulfate hexahydrate (CoSO4 6H2O) weighing.00 g


1) Note that there is water in the equation. An example of a hydrate

154 grams is how much weight is contributed by the CoSO4. 994 g

Six moles of water has a weight of 18 grams. 015 x 6 = 108 09 g

CoSO4 6H2O has a molar mass equal to 263. 084 g/mol

Formula for determining the number of moles from grams

5.00 g / 263 084 g/mol = 0 0190 mol

In case number seven, let's say that a given sample has no CaSO4 12H2O, 900 g A molecular count of how many


1) It is a hydrate because water is present. Keep in mind that the dot in the middle is not a multiplier.

CaSO4 has a lone weight of 136 139 g

It has a mass of 18 grams per half mole of water. 015 x 0 5 = 9 0075 g

Moles of CaSO4 12H2O weigh in at 145 1465 g/mol

Step 2: Change the gram weight to the molecular weight.

0.900 g / 145 1465 g/mol = 0 3 significant figures =.00620 mol

Three, the formula is sometimes written like this:

CaSO4⋅ 0 5H2O

The number of oxygen atoms in three Only 78g of water How many H atoms are there?


First, use the standard procedure for converting grams to moles:

3.78 g / 18 015 g/mol = 0 209825 mol

Then, using Avogadro's Number, we can convert moles to molecules.

(0 209825 mol) (6 022 x 1023 mol¯1) = 1 About 26 x 1023 molecules (with three significant figures).

Thirdly, there is an oxygen atom in every molecule of water (H2O). So, 1 261023 oxygen atoms in a 33333333 78 grams of liquid

4) There are 2 water molecules because there are 2 hydrogen atoms. 52 x 1023 hydrogen atoms per 3 Amount of water required: 78 g

Use this link to go back to the Mole index.

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